1 /*
2 * Copyright (c) 2000, 2025, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package jdk.internal.misc;
27
28 import jdk.internal.vm.annotation.AOTRuntimeSetup;
29 import jdk.internal.vm.annotation.AOTSafeClassInitializer;
30 import jdk.internal.vm.annotation.ForceInline;
31 import jdk.internal.vm.annotation.IntrinsicCandidate;
32 import sun.nio.Cleaner;
33 import sun.nio.ch.DirectBuffer;
34
35 import java.lang.reflect.Field;
36 import java.security.ProtectionDomain;
37
38 import static jdk.internal.misc.UnsafeConstants.*;
39
40 /**
41 * A collection of methods for performing low-level, unsafe operations.
42 * Although the class and all methods are public, use of this class is
43 * limited because only trusted code can obtain instances of it.
44 *
45 * <em>Note:</em> It is the responsibility of the caller to make sure
46 * arguments are checked before methods of this class are
47 * called. While some rudimentary checks are performed on the input,
48 * the checks are best effort and when performance is an overriding
49 * priority, as when methods of this class are optimized by the
50 * runtime compiler, some or all checks (if any) may be elided. Hence,
51 * the caller must not rely on the checks and corresponding
52 * exceptions!
53 *
54 * @author John R. Rose
55 * @see #getUnsafe
56 */
57 @AOTSafeClassInitializer
58 public final class Unsafe {
59
60 private static native void registerNatives();
61 static {
62 runtimeSetup();
63 }
64
65 /// BASE_OFFSET, INDEX_SCALE, and ADDRESS_SIZE fields are equivalent if the
66 /// AOT initialized heap is reused, so just register natives
67 @AOTRuntimeSetup
68 private static void runtimeSetup() {
69 registerNatives();
70 }
71
72 private Unsafe() {}
169 * The first two parameters are interpreted exactly as with
170 * {@link #getInt(Object, long)} to refer to a specific
171 * Java variable (field or array element). The given value
172 * is stored into that variable.
173 * <p>
174 * The variable must be of the same type as the method
175 * parameter {@code x}.
176 *
177 * @param o Java heap object in which the variable resides, if any, else
178 * null
179 * @param offset indication of where the variable resides in a Java heap
180 * object, if any, else a memory address locating the variable
181 * statically
182 * @param x the value to store into the indicated Java variable
183 * @throws RuntimeException No defined exceptions are thrown, not even
184 * {@link NullPointerException}
185 */
186 @IntrinsicCandidate
187 public native void putInt(Object o, long offset, int x);
188
189 /**
190 * Fetches a reference value from a given Java variable.
191 * @see #getInt(Object, long)
192 */
193 @IntrinsicCandidate
194 public native Object getReference(Object o, long offset);
195
196 /**
197 * Stores a reference value into a given Java variable.
198 * <p>
199 * Unless the reference {@code x} being stored is either null
200 * or matches the field type, the results are undefined.
201 * If the reference {@code o} is non-null, card marks or
202 * other store barriers for that object (if the VM requires them)
203 * are updated.
204 * @see #putInt(Object, long, int)
205 */
206 @IntrinsicCandidate
207 public native void putReference(Object o, long offset, Object x);
208
209 /** @see #getInt(Object, long) */
210 @IntrinsicCandidate
211 public native boolean getBoolean(Object o, long offset);
212
213 /** @see #putInt(Object, long, int) */
214 @IntrinsicCandidate
215 public native void putBoolean(Object o, long offset, boolean x);
216
217 /** @see #getInt(Object, long) */
218 @IntrinsicCandidate
219 public native byte getByte(Object o, long offset);
220
221 /** @see #putInt(Object, long, int) */
222 @IntrinsicCandidate
223 public native void putByte(Object o, long offset, byte x);
224
225 /** @see #getInt(Object, long) */
226 @IntrinsicCandidate
227 public native short getShort(Object o, long offset);
228
1178 }
1179
1180 /**
1181 * Ensures the given class has been initialized (see JVMS-5.5 for details).
1182 * This is often needed in conjunction with obtaining the static field base
1183 * of a class.
1184 *
1185 * The call returns when either class {@code c} is fully initialized or
1186 * class {@code c} is being initialized and the call is performed from
1187 * the initializing thread. In the latter case a subsequent call to
1188 * {@link #shouldBeInitialized} will return {@code true}.
1189 */
1190 public void ensureClassInitialized(Class<?> c) {
1191 if (c == null) {
1192 throw new NullPointerException();
1193 }
1194
1195 ensureClassInitialized0(c);
1196 }
1197
1198 /**
1199 * Reports the offset of the first element in the storage allocation of a
1200 * given array class. If {@link #arrayIndexScale} returns a non-zero value
1201 * for the same class, you may use that scale factor, together with this
1202 * base offset, to form new offsets to access elements of arrays of the
1203 * given class.
1204 * <p>
1205 * The return value is in the range of a {@code int}. The return type is
1206 * {@code long} to emphasize that long arithmetic should always be used
1207 * for offset calculations to avoid overflows.
1208 *
1209 * @see #getInt(Object, long)
1210 * @see #putInt(Object, long, int)
1211 */
1212 public long arrayBaseOffset(Class<?> arrayClass) {
1213 if (arrayClass == null) {
1214 throw new NullPointerException();
1215 }
1216
1217 return arrayBaseOffset0(arrayClass);
1218 }
1219
1220
1221 /** The value of {@code arrayBaseOffset(boolean[].class)} */
1222 public static final long ARRAY_BOOLEAN_BASE_OFFSET
1223 = theUnsafe.arrayBaseOffset(boolean[].class);
1224
1225 /** The value of {@code arrayBaseOffset(byte[].class)} */
1226 public static final long ARRAY_BYTE_BASE_OFFSET
1227 = theUnsafe.arrayBaseOffset(byte[].class);
1228
1229 /** The value of {@code arrayBaseOffset(short[].class)} */
1230 public static final long ARRAY_SHORT_BASE_OFFSET
1231 = theUnsafe.arrayBaseOffset(short[].class);
1232
1233 /** The value of {@code arrayBaseOffset(char[].class)} */
1234 public static final long ARRAY_CHAR_BASE_OFFSET
1235 = theUnsafe.arrayBaseOffset(char[].class);
1236
1237 /** The value of {@code arrayBaseOffset(int[].class)} */
1238 public static final long ARRAY_INT_BASE_OFFSET
1239 = theUnsafe.arrayBaseOffset(int[].class);
1246 public static final long ARRAY_FLOAT_BASE_OFFSET
1247 = theUnsafe.arrayBaseOffset(float[].class);
1248
1249 /** The value of {@code arrayBaseOffset(double[].class)} */
1250 public static final long ARRAY_DOUBLE_BASE_OFFSET
1251 = theUnsafe.arrayBaseOffset(double[].class);
1252
1253 /** The value of {@code arrayBaseOffset(Object[].class)} */
1254 public static final long ARRAY_OBJECT_BASE_OFFSET
1255 = theUnsafe.arrayBaseOffset(Object[].class);
1256
1257 /**
1258 * Reports the scale factor for addressing elements in the storage
1259 * allocation of a given array class. However, arrays of "narrow" types
1260 * will generally not work properly with accessors like {@link
1261 * #getByte(Object, long)}, so the scale factor for such classes is reported
1262 * as zero.
1263 * <p>
1264 * The computation of the actual memory offset should always use {@code
1265 * long} arithmetic to avoid overflows.
1266 *
1267 * @see #arrayBaseOffset
1268 * @see #getInt(Object, long)
1269 * @see #putInt(Object, long, int)
1270 */
1271 public int arrayIndexScale(Class<?> arrayClass) {
1272 if (arrayClass == null) {
1273 throw new NullPointerException();
1274 }
1275
1276 return arrayIndexScale0(arrayClass);
1277 }
1278
1279
1280 /** The value of {@code arrayIndexScale(boolean[].class)} */
1281 public static final int ARRAY_BOOLEAN_INDEX_SCALE
1282 = theUnsafe.arrayIndexScale(boolean[].class);
1283
1284 /** The value of {@code arrayIndexScale(byte[].class)} */
1285 public static final int ARRAY_BYTE_INDEX_SCALE
1286 = theUnsafe.arrayIndexScale(byte[].class);
1287
1288 /** The value of {@code arrayIndexScale(short[].class)} */
1289 public static final int ARRAY_SHORT_INDEX_SCALE
1290 = theUnsafe.arrayIndexScale(short[].class);
1291
1292 /** The value of {@code arrayIndexScale(char[].class)} */
1293 public static final int ARRAY_CHAR_INDEX_SCALE
1294 = theUnsafe.arrayIndexScale(char[].class);
1295
1296 /** The value of {@code arrayIndexScale(int[].class)} */
1297 public static final int ARRAY_INT_INDEX_SCALE
1298 = theUnsafe.arrayIndexScale(int[].class);
1362 public Class<?> defineClass(String name, byte[] b, int off, int len,
1363 ClassLoader loader,
1364 ProtectionDomain protectionDomain) {
1365 if (b == null) {
1366 throw new NullPointerException();
1367 }
1368 if (len < 0) {
1369 throw new ArrayIndexOutOfBoundsException();
1370 }
1371
1372 return defineClass0(name, b, off, len, loader, protectionDomain);
1373 }
1374
1375 public native Class<?> defineClass0(String name, byte[] b, int off, int len,
1376 ClassLoader loader,
1377 ProtectionDomain protectionDomain);
1378
1379 /**
1380 * Allocates an instance but does not run any constructor.
1381 * Initializes the class if it has not yet been.
1382 */
1383 @IntrinsicCandidate
1384 public native Object allocateInstance(Class<?> cls)
1385 throws InstantiationException;
1386
1387 /**
1388 * Allocates an array of a given type, but does not do zeroing.
1389 * <p>
1390 * This method should only be used in the very rare cases where a high-performance code
1391 * overwrites the destination array completely, and compilers cannot assist in zeroing elimination.
1392 * In an overwhelming majority of cases, a normal Java allocation should be used instead.
1393 * <p>
1394 * Users of this method are <b>required</b> to overwrite the initial (garbage) array contents
1395 * before allowing untrusted code, or code in other threads, to observe the reference
1396 * to the newly allocated array. In addition, the publication of the array reference must be
1397 * safe according to the Java Memory Model requirements.
1398 * <p>
1399 * The safest approach to deal with an uninitialized array is to keep the reference to it in local
1400 * variable at least until the initialization is complete, and then publish it <b>once</b>, either
1401 * by writing it to a <em>volatile</em> field, or storing it into a <em>final</em> field in constructor,
1437 return null;
1438 }
1439
1440 /** Throws the exception without telling the verifier. */
1441 public native void throwException(Throwable ee);
1442
1443 /**
1444 * Atomically updates Java variable to {@code x} if it is currently
1445 * holding {@code expected}.
1446 *
1447 * <p>This operation has memory semantics of a {@code volatile} read
1448 * and write. Corresponds to C11 atomic_compare_exchange_strong.
1449 *
1450 * @return {@code true} if successful
1451 */
1452 @IntrinsicCandidate
1453 public final native boolean compareAndSetReference(Object o, long offset,
1454 Object expected,
1455 Object x);
1456
1457 @IntrinsicCandidate
1458 public final native Object compareAndExchangeReference(Object o, long offset,
1459 Object expected,
1460 Object x);
1461
1462 @IntrinsicCandidate
1463 public final Object compareAndExchangeReferenceAcquire(Object o, long offset,
1464 Object expected,
1465 Object x) {
1466 return compareAndExchangeReference(o, offset, expected, x);
1467 }
1468
1469 @IntrinsicCandidate
1470 public final Object compareAndExchangeReferenceRelease(Object o, long offset,
1471 Object expected,
1472 Object x) {
1473 return compareAndExchangeReference(o, offset, expected, x);
1474 }
1475
1476 @IntrinsicCandidate
1477 public final boolean weakCompareAndSetReferencePlain(Object o, long offset,
1478 Object expected,
1479 Object x) {
1480 return compareAndSetReference(o, offset, expected, x);
1481 }
1482
1483 @IntrinsicCandidate
1484 public final boolean weakCompareAndSetReferenceAcquire(Object o, long offset,
1485 Object expected,
1486 Object x) {
1487 return compareAndSetReference(o, offset, expected, x);
1488 }
1489
1490 @IntrinsicCandidate
1491 public final boolean weakCompareAndSetReferenceRelease(Object o, long offset,
1492 Object expected,
1493 Object x) {
1494 return compareAndSetReference(o, offset, expected, x);
1495 }
1496
1497 @IntrinsicCandidate
1498 public final boolean weakCompareAndSetReference(Object o, long offset,
1499 Object expected,
1500 Object x) {
1501 return compareAndSetReference(o, offset, expected, x);
1502 }
1503
1504 /**
1505 * Atomically updates Java variable to {@code x} if it is currently
1506 * holding {@code expected}.
1507 *
1508 * <p>This operation has memory semantics of a {@code volatile} read
1509 * and write. Corresponds to C11 atomic_compare_exchange_strong.
1510 *
1511 * @return {@code true} if successful
1512 */
1513 @IntrinsicCandidate
1514 public final native boolean compareAndSetInt(Object o, long offset,
1515 int expected,
1516 int x);
1517
1518 @IntrinsicCandidate
1519 public final native int compareAndExchangeInt(Object o, long offset,
1520 int expected,
1521 int x);
1522
1523 @IntrinsicCandidate
2099 public final boolean weakCompareAndSetLongRelease(Object o, long offset,
2100 long expected,
2101 long x) {
2102 return compareAndSetLong(o, offset, expected, x);
2103 }
2104
2105 @IntrinsicCandidate
2106 public final boolean weakCompareAndSetLong(Object o, long offset,
2107 long expected,
2108 long x) {
2109 return compareAndSetLong(o, offset, expected, x);
2110 }
2111
2112 /**
2113 * Fetches a reference value from a given Java variable, with volatile
2114 * load semantics. Otherwise identical to {@link #getReference(Object, long)}
2115 */
2116 @IntrinsicCandidate
2117 public native Object getReferenceVolatile(Object o, long offset);
2118
2119 /**
2120 * Stores a reference value into a given Java variable, with
2121 * volatile store semantics. Otherwise identical to {@link #putReference(Object, long, Object)}
2122 */
2123 @IntrinsicCandidate
2124 public native void putReferenceVolatile(Object o, long offset, Object x);
2125
2126 /** Volatile version of {@link #getInt(Object, long)} */
2127 @IntrinsicCandidate
2128 public native int getIntVolatile(Object o, long offset);
2129
2130 /** Volatile version of {@link #putInt(Object, long, int)} */
2131 @IntrinsicCandidate
2132 public native void putIntVolatile(Object o, long offset, int x);
2133
2134 /** Volatile version of {@link #getBoolean(Object, long)} */
2135 @IntrinsicCandidate
2136 public native boolean getBooleanVolatile(Object o, long offset);
2137
2138 /** Volatile version of {@link #putBoolean(Object, long, boolean)} */
2139 @IntrinsicCandidate
2140 public native void putBooleanVolatile(Object o, long offset, boolean x);
2141
2142 /** Volatile version of {@link #getByte(Object, long)} */
2143 @IntrinsicCandidate
2144 public native byte getByteVolatile(Object o, long offset);
2145
2178 /** Volatile version of {@link #putFloat(Object, long, float)} */
2179 @IntrinsicCandidate
2180 public native void putFloatVolatile(Object o, long offset, float x);
2181
2182 /** Volatile version of {@link #getDouble(Object, long)} */
2183 @IntrinsicCandidate
2184 public native double getDoubleVolatile(Object o, long offset);
2185
2186 /** Volatile version of {@link #putDouble(Object, long, double)} */
2187 @IntrinsicCandidate
2188 public native void putDoubleVolatile(Object o, long offset, double x);
2189
2190
2191
2192 /** Acquire version of {@link #getReferenceVolatile(Object, long)} */
2193 @IntrinsicCandidate
2194 public final Object getReferenceAcquire(Object o, long offset) {
2195 return getReferenceVolatile(o, offset);
2196 }
2197
2198 /** Acquire version of {@link #getBooleanVolatile(Object, long)} */
2199 @IntrinsicCandidate
2200 public final boolean getBooleanAcquire(Object o, long offset) {
2201 return getBooleanVolatile(o, offset);
2202 }
2203
2204 /** Acquire version of {@link #getByteVolatile(Object, long)} */
2205 @IntrinsicCandidate
2206 public final byte getByteAcquire(Object o, long offset) {
2207 return getByteVolatile(o, offset);
2208 }
2209
2210 /** Acquire version of {@link #getShortVolatile(Object, long)} */
2211 @IntrinsicCandidate
2212 public final short getShortAcquire(Object o, long offset) {
2213 return getShortVolatile(o, offset);
2214 }
2215
2216 /** Acquire version of {@link #getCharVolatile(Object, long)} */
2217 @IntrinsicCandidate
2242 public final double getDoubleAcquire(Object o, long offset) {
2243 return getDoubleVolatile(o, offset);
2244 }
2245
2246 /*
2247 * Versions of {@link #putReferenceVolatile(Object, long, Object)}
2248 * that do not guarantee immediate visibility of the store to
2249 * other threads. This method is generally only useful if the
2250 * underlying field is a Java volatile (or if an array cell, one
2251 * that is otherwise only accessed using volatile accesses).
2252 *
2253 * Corresponds to C11 atomic_store_explicit(..., memory_order_release).
2254 */
2255
2256 /** Release version of {@link #putReferenceVolatile(Object, long, Object)} */
2257 @IntrinsicCandidate
2258 public final void putReferenceRelease(Object o, long offset, Object x) {
2259 putReferenceVolatile(o, offset, x);
2260 }
2261
2262 /** Release version of {@link #putBooleanVolatile(Object, long, boolean)} */
2263 @IntrinsicCandidate
2264 public final void putBooleanRelease(Object o, long offset, boolean x) {
2265 putBooleanVolatile(o, offset, x);
2266 }
2267
2268 /** Release version of {@link #putByteVolatile(Object, long, byte)} */
2269 @IntrinsicCandidate
2270 public final void putByteRelease(Object o, long offset, byte x) {
2271 putByteVolatile(o, offset, x);
2272 }
2273
2274 /** Release version of {@link #putShortVolatile(Object, long, short)} */
2275 @IntrinsicCandidate
2276 public final void putShortRelease(Object o, long offset, short x) {
2277 putShortVolatile(o, offset, x);
2278 }
2279
2280 /** Release version of {@link #putCharVolatile(Object, long, char)} */
2281 @IntrinsicCandidate
2298 /** Release version of {@link #putLongVolatile(Object, long, long)} */
2299 @IntrinsicCandidate
2300 public final void putLongRelease(Object o, long offset, long x) {
2301 putLongVolatile(o, offset, x);
2302 }
2303
2304 /** Release version of {@link #putDoubleVolatile(Object, long, double)} */
2305 @IntrinsicCandidate
2306 public final void putDoubleRelease(Object o, long offset, double x) {
2307 putDoubleVolatile(o, offset, x);
2308 }
2309
2310 // ------------------------------ Opaque --------------------------------------
2311
2312 /** Opaque version of {@link #getReferenceVolatile(Object, long)} */
2313 @IntrinsicCandidate
2314 public final Object getReferenceOpaque(Object o, long offset) {
2315 return getReferenceVolatile(o, offset);
2316 }
2317
2318 /** Opaque version of {@link #getBooleanVolatile(Object, long)} */
2319 @IntrinsicCandidate
2320 public final boolean getBooleanOpaque(Object o, long offset) {
2321 return getBooleanVolatile(o, offset);
2322 }
2323
2324 /** Opaque version of {@link #getByteVolatile(Object, long)} */
2325 @IntrinsicCandidate
2326 public final byte getByteOpaque(Object o, long offset) {
2327 return getByteVolatile(o, offset);
2328 }
2329
2330 /** Opaque version of {@link #getShortVolatile(Object, long)} */
2331 @IntrinsicCandidate
2332 public final short getShortOpaque(Object o, long offset) {
2333 return getShortVolatile(o, offset);
2334 }
2335
2336 /** Opaque version of {@link #getCharVolatile(Object, long)} */
2337 @IntrinsicCandidate
2352 }
2353
2354 /** Opaque version of {@link #getLongVolatile(Object, long)} */
2355 @IntrinsicCandidate
2356 public final long getLongOpaque(Object o, long offset) {
2357 return getLongVolatile(o, offset);
2358 }
2359
2360 /** Opaque version of {@link #getDoubleVolatile(Object, long)} */
2361 @IntrinsicCandidate
2362 public final double getDoubleOpaque(Object o, long offset) {
2363 return getDoubleVolatile(o, offset);
2364 }
2365
2366 /** Opaque version of {@link #putReferenceVolatile(Object, long, Object)} */
2367 @IntrinsicCandidate
2368 public final void putReferenceOpaque(Object o, long offset, Object x) {
2369 putReferenceVolatile(o, offset, x);
2370 }
2371
2372 /** Opaque version of {@link #putBooleanVolatile(Object, long, boolean)} */
2373 @IntrinsicCandidate
2374 public final void putBooleanOpaque(Object o, long offset, boolean x) {
2375 putBooleanVolatile(o, offset, x);
2376 }
2377
2378 /** Opaque version of {@link #putByteVolatile(Object, long, byte)} */
2379 @IntrinsicCandidate
2380 public final void putByteOpaque(Object o, long offset, byte x) {
2381 putByteVolatile(o, offset, x);
2382 }
2383
2384 /** Opaque version of {@link #putShortVolatile(Object, long, short)} */
2385 @IntrinsicCandidate
2386 public final void putShortOpaque(Object o, long offset, short x) {
2387 putShortVolatile(o, offset, x);
2388 }
2389
2390 /** Opaque version of {@link #putCharVolatile(Object, long, char)} */
2391 @IntrinsicCandidate
2400 }
2401
2402 /** Opaque version of {@link #putFloatVolatile(Object, long, float)} */
2403 @IntrinsicCandidate
2404 public final void putFloatOpaque(Object o, long offset, float x) {
2405 putFloatVolatile(o, offset, x);
2406 }
2407
2408 /** Opaque version of {@link #putLongVolatile(Object, long, long)} */
2409 @IntrinsicCandidate
2410 public final void putLongOpaque(Object o, long offset, long x) {
2411 putLongVolatile(o, offset, x);
2412 }
2413
2414 /** Opaque version of {@link #putDoubleVolatile(Object, long, double)} */
2415 @IntrinsicCandidate
2416 public final void putDoubleOpaque(Object o, long offset, double x) {
2417 putDoubleVolatile(o, offset, x);
2418 }
2419
2420 /**
2421 * Unblocks the given thread blocked on {@code park}, or, if it is
2422 * not blocked, causes the subsequent call to {@code park} not to
2423 * block. Note: this operation is "unsafe" solely because the
2424 * caller must somehow ensure that the thread has not been
2425 * destroyed. Nothing special is usually required to ensure this
2426 * when called from Java (in which there will ordinarily be a live
2427 * reference to the thread) but this is not nearly-automatically
2428 * so when calling from native code.
2429 *
2430 * @param thread the thread to unpark.
2431 */
2432 @IntrinsicCandidate
2433 public native void unpark(Object thread);
2434
2435 /**
2436 * Blocks current thread, returning when a balancing
2437 * {@code unpark} occurs, or a balancing {@code unpark} has
2438 * already occurred, or the thread is interrupted, or, if not
2439 * absolute and time is not zero, the given time nanoseconds have
2786 /**
2787 * Atomically exchanges the given reference value with the current
2788 * reference value of a field or array element within the given
2789 * object {@code o} at the given {@code offset}.
2790 *
2791 * @param o object/array to update the field/element in
2792 * @param offset field/element offset
2793 * @param newValue new value
2794 * @return the previous value
2795 * @since 1.8
2796 */
2797 @IntrinsicCandidate
2798 public final Object getAndSetReference(Object o, long offset, Object newValue) {
2799 Object v;
2800 do {
2801 v = getReferenceVolatile(o, offset);
2802 } while (!weakCompareAndSetReference(o, offset, v, newValue));
2803 return v;
2804 }
2805
2806 @ForceInline
2807 public final Object getAndSetReferenceRelease(Object o, long offset, Object newValue) {
2808 Object v;
2809 do {
2810 v = getReference(o, offset);
2811 } while (!weakCompareAndSetReferenceRelease(o, offset, v, newValue));
2812 return v;
2813 }
2814
2815 @ForceInline
2816 public final Object getAndSetReferenceAcquire(Object o, long offset, Object newValue) {
2817 Object v;
2818 do {
2819 v = getReferenceAcquire(o, offset);
2820 } while (!weakCompareAndSetReferenceAcquire(o, offset, v, newValue));
2821 return v;
2822 }
2823
2824 @IntrinsicCandidate
2825 public final byte getAndSetByte(Object o, long offset, byte newValue) {
2826 byte v;
2827 do {
2828 v = getByteVolatile(o, offset);
2829 } while (!weakCompareAndSetByte(o, offset, v, newValue));
2830 return v;
2831 }
2832
2833 @ForceInline
2834 public final byte getAndSetByteRelease(Object o, long offset, byte newValue) {
2835 byte v;
2836 do {
2837 v = getByte(o, offset);
2838 } while (!weakCompareAndSetByteRelease(o, offset, v, newValue));
2839 return v;
2840 }
2841
2842 @ForceInline
2843 public final byte getAndSetByteAcquire(Object o, long offset, byte newValue) {
3859 private static short convEndian(boolean big, short n) { return big == BIG_ENDIAN ? n : Short.reverseBytes(n) ; }
3860 private static int convEndian(boolean big, int n) { return big == BIG_ENDIAN ? n : Integer.reverseBytes(n) ; }
3861 private static long convEndian(boolean big, long n) { return big == BIG_ENDIAN ? n : Long.reverseBytes(n) ; }
3862
3863
3864
3865 private native long allocateMemory0(long bytes);
3866 private native long reallocateMemory0(long address, long bytes);
3867 private native void freeMemory0(long address);
3868 @IntrinsicCandidate
3869 private native void setMemory0(Object o, long offset, long bytes, byte value);
3870 @IntrinsicCandidate
3871 private native void copyMemory0(Object srcBase, long srcOffset, Object destBase, long destOffset, long bytes);
3872 private native void copySwapMemory0(Object srcBase, long srcOffset, Object destBase, long destOffset, long bytes, long elemSize);
3873 private native long objectFieldOffset0(Field f); // throws IAE
3874 private native long knownObjectFieldOffset0(Class<?> c, String name); // error code: -1 not found, -2 static
3875 private native long staticFieldOffset0(Field f); // throws IAE
3876 private native Object staticFieldBase0(Field f); // throws IAE
3877 private native boolean shouldBeInitialized0(Class<?> c);
3878 private native void ensureClassInitialized0(Class<?> c);
3879 private native int arrayBaseOffset0(Class<?> arrayClass); // public version returns long to promote correct arithmetic
3880 private native int arrayIndexScale0(Class<?> arrayClass);
3881 private native int getLoadAverage0(double[] loadavg, int nelems);
3882
3883
3884 /**
3885 * Invokes the given direct byte buffer's cleaner, if any.
3886 *
3887 * @param directBuffer a direct byte buffer
3888 * @throws NullPointerException if {@code directBuffer} is null
3889 * @throws IllegalArgumentException if {@code directBuffer} is non-direct,
3890 * or is a {@link java.nio.Buffer#slice slice}, or is a
3891 * {@link java.nio.Buffer#duplicate duplicate}
3892 */
3893 public void invokeCleaner(java.nio.ByteBuffer directBuffer) {
3894 if (!directBuffer.isDirect())
3895 throw new IllegalArgumentException("buffer is non-direct");
3896
3897 DirectBuffer db = (DirectBuffer) directBuffer;
3898 if (db.attachment() != null)
3899 throw new IllegalArgumentException("duplicate or slice");
3900
3901 Cleaner cleaner = db.cleaner();
|
1 /*
2 * Copyright (c) 2000, 2026, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package jdk.internal.misc;
27
28 import jdk.internal.vm.annotation.AOTRuntimeSetup;
29 import jdk.internal.vm.annotation.AOTSafeClassInitializer;
30 import jdk.internal.vm.annotation.ForceInline;
31 import jdk.internal.vm.annotation.IntrinsicCandidate;
32 import jdk.internal.value.ValueClass;
33 import sun.nio.Cleaner;
34 import sun.nio.ch.DirectBuffer;
35
36 import java.lang.reflect.Field;
37 import java.security.ProtectionDomain;
38
39 import static jdk.internal.misc.UnsafeConstants.*;
40
41 /**
42 * A collection of methods for performing low-level, unsafe operations.
43 * Although the class and all methods are public, use of this class is
44 * limited because only trusted code can obtain instances of it.
45 *
46 * <h2><a id="undefined-behavior">Undefined Behavior</a></h2>
47 * For performance reasons, {@code Unsafe} is allowed to work outside the
48 * restrictions enforced by the JVM. As a result, it is the responsibility of
49 * the caller to ensure that an invocation of an {@code Unsafe} method is
50 * conformant, and failure to do so will result in undefined behavior. The
51 * runtime and the JIT compiler may assume that undefined behavior never
52 * happens, and operate accordingly. For example, the runtime assumes that each
53 * object has a header with a particular layout, and if the users use
54 * {@code Unsafe} to overwrite this header with invalid data, the behavior of
55 * the runtime becomes unpredictable. Another example is that the JIT compiler
56 * may assume that accesses on separate objects are unrelated, and schedule
57 * each of them without taking into consideration the others. If there is an
58 * {@code Unsafe} access that is out of bounds and points to object different
59 * from the declared base, the program may execute in a way that a variable
60 * seems to have multiple values at the same time. As a result, when a program
61 * exhibits undefined behavior, there is no restrictions on its behaviors. Such
62 * behaviors may include but not be limited to:
63 *
64 * <ul>
65 * <li>Working as expected.
66 * <li>Crashing the VM.
67 * <li>Corruption of the heap or JVM memory.
68 * <li>Nonsensical variable value. E.g. an {@code int} may appear to be
69 * simultaneously 0 and 1.
70 * <li>Impossible code execution. E.g. the branches of an {@code if} are
71 * both executed or both not executed.
72 * <li>Wiping out the hard drive.
73 * </ul>
74 *
75 * Undefined behavior, as described in this class, is analogous to the
76 * terminology with the same name in the C++ language.
77 * <p>
78 * Some methods (e.g. {@link #getInt}) exhibit undefined behavior if they
79 * are invoked at runtime with illegal arguments. This means that they will
80 * never exhibit undefined behavior if they are not actually reachable at
81 * runtime. On the other hands, other methods (e.g.
82 * {@link #allocateInstance(Class)}) exhibit undefined behavior if they are
83 * used incorrectly, even if the invocation may not be reachable at runtime.
84 * The analogous terminology in C++ is that such programs are ill-formed.
85 * <p>
86 * For methods exhibiting undefined behavior if they are invoked at runtime
87 * with illegal arguments, undefined behavior may time travel. That is, if a
88 * control path may eventually reach an invocation of an {@code Unsafe} method
89 * with illegal arguments, the symptoms of undefined behavior may be present
90 * even before the invocation of the {@code Unsafe} method. This is because the
91 * JIT compiler may have certain assumptions about the inputs of an
92 * {@code Unsafe} invocation, these assumptions may propagate backward to
93 * previous statements, leading to wrong executions if the assumptions are
94 * invalid.
95 *
96 * @author John R. Rose
97 * @see #getUnsafe
98 */
99 @AOTSafeClassInitializer
100 public final class Unsafe {
101
102 private static native void registerNatives();
103 static {
104 runtimeSetup();
105 }
106
107 /// BASE_OFFSET, INDEX_SCALE, and ADDRESS_SIZE fields are equivalent if the
108 /// AOT initialized heap is reused, so just register natives
109 @AOTRuntimeSetup
110 private static void runtimeSetup() {
111 registerNatives();
112 }
113
114 private Unsafe() {}
211 * The first two parameters are interpreted exactly as with
212 * {@link #getInt(Object, long)} to refer to a specific
213 * Java variable (field or array element). The given value
214 * is stored into that variable.
215 * <p>
216 * The variable must be of the same type as the method
217 * parameter {@code x}.
218 *
219 * @param o Java heap object in which the variable resides, if any, else
220 * null
221 * @param offset indication of where the variable resides in a Java heap
222 * object, if any, else a memory address locating the variable
223 * statically
224 * @param x the value to store into the indicated Java variable
225 * @throws RuntimeException No defined exceptions are thrown, not even
226 * {@link NullPointerException}
227 */
228 @IntrinsicCandidate
229 public native void putInt(Object o, long offset, int x);
230
231 /**
232 * Returns true if the given field is flattened.
233 */
234 public boolean isFlatField(Field f) {
235 if (f == null) {
236 throw new NullPointerException();
237 }
238 return isFlatField0(f);
239 }
240
241 private native boolean isFlatField0(Object o);
242
243 /* Returns true if the given field has a null marker
244 * <p>
245 * Nullable flat fields are stored in a flattened representation
246 * and have an associated null marker to indicate if the the field value is
247 * null or the one stored with the flat representation
248 */
249
250 public boolean hasNullMarker(Field f) {
251 if (f == null) {
252 throw new NullPointerException();
253 }
254 return hasNullMarker0(f);
255 }
256
257 private native boolean hasNullMarker0(Object o);
258
259 /* Returns the offset of the null marker of the field,
260 * or -1 if the field doesn't have a null marker
261 */
262
263 public int nullMarkerOffset(Field f) {
264 if (f == null) {
265 throw new NullPointerException();
266 }
267 return nullMarkerOffset0(f);
268 }
269
270 private native int nullMarkerOffset0(Object o);
271
272 public static final int NON_FLAT_LAYOUT = 0;
273
274 /* Reports the kind of layout used for an element in the storage
275 * allocation of the given array. Do not expect to perform any logic
276 * or layout control with this value, it is just an opaque token
277 * used for performance reasons.
278 *
279 * A layout of 0 indicates this array is not flat.
280 */
281 public int arrayLayout(Object[] array) {
282 if (array == null) {
283 throw new NullPointerException();
284 }
285 return arrayLayout0(array);
286 }
287
288 @IntrinsicCandidate
289 private native int arrayLayout0(Object[] array);
290
291
292 /* Reports the kind of layout used for a given field in the storage
293 * allocation of its class. Do not expect to perform any logic
294 * or layout control with this value, it is just an opaque token
295 * used for performance reasons.
296 *
297 * A layout of 0 indicates this field is not flat.
298 */
299 public int fieldLayout(Field f) {
300 if (f == null) {
301 throw new NullPointerException();
302 }
303 return fieldLayout0(f);
304 }
305
306 private native int fieldLayout0(Object o);
307
308 public native Object[] newSpecialArray(Class<?> componentType,
309 int length, int layoutKind);
310
311 /**
312 * Fetches a reference value from a given Java variable.
313 * This method can return a reference to either an object or value
314 * or a null reference.
315 *
316 * @see #getInt(Object, long)
317 */
318 @IntrinsicCandidate
319 public native Object getReference(Object o, long offset);
320
321 /**
322 * Stores a reference value into a given Java variable.
323 * This method can store a reference to either an object or value
324 * or a null reference.
325 * <p>
326 * Unless the reference {@code x} being stored is either null
327 * or matches the field type, the results are undefined.
328 * If the reference {@code o} is non-null, card marks or
329 * other store barriers for that object (if the VM requires them)
330 * are updated.
331 * @see #putInt(Object, long, int)
332 */
333 @IntrinsicCandidate
334 public native void putReference(Object o, long offset, Object x);
335
336 /**
337 * Fetches a value of type {@code <V>} from a given Java variable.
338 * More specifically, fetches a field or array element within the given
339 * {@code o} object at the given offset, or (if {@code o} is null)
340 * from the memory address whose numerical value is the given offset.
341 *
342 * @apiNote
343 * The returned object is newly allocated into the heap, because flat
344 * values lack object headers and thus can't be used as objects directly.
345 *
346 * @param o Java heap object in which the variable resides, if any, else
347 * null
348 * @param offset indication of where the variable resides in a Java heap
349 * object, if any, else a memory address locating the variable
350 * statically
351 * @param layoutKind opaque value used by the VM to know the layout
352 * the field or array element. This value must be retrieved with
353 * {@link #fieldLayout} or {@link #arrayLayout}.
354 * @param valueType value type
355 * @param <V> the type of a value
356 * @return the value fetched from the indicated Java variable
357 * @throws RuntimeException No defined exceptions are thrown, not even
358 * {@link NullPointerException}
359 */
360 @IntrinsicCandidate
361 public native <V> V getFlatValue(Object o, long offset, int layoutKind, Class<?> valueType);
362
363 /**
364 * Stores the given value into a given Java variable.
365 *
366 * Unless the reference {@code o} being stored is either null
367 * or matches the field type, the results are undefined.
368 *
369 * @param o Java heap object in which the variable resides, if any, else
370 * null
371 * @param offset indication of where the variable resides in a Java heap
372 * object, if any, else a memory address locating the variable
373 * statically
374 * @param layoutKind opaque value used by the VM to know the layout
375 * the field or array element. This value must be retrieved with
376 * {@link #fieldLayout} or {@link #arrayLayout}.
377 * @param valueType value type
378 * @param v the value to store into the indicated Java variable
379 * @param <V> the type of a value
380 * @throws RuntimeException No defined exceptions are thrown, not even
381 * {@link NullPointerException}
382 */
383 @IntrinsicCandidate
384 public native <V> void putFlatValue(Object o, long offset, int layoutKind, Class<?> valueType, V v);
385
386 /**
387 * Returns the header size of the given value type.
388 *
389 * @param valueType value type
390 * @return the header size of the value type
391 */
392 public native <V> long valueHeaderSize(Class<V> valueType);
393
394 /** @see #getInt(Object, long) */
395 @IntrinsicCandidate
396 public native boolean getBoolean(Object o, long offset);
397
398 /** @see #putInt(Object, long, int) */
399 @IntrinsicCandidate
400 public native void putBoolean(Object o, long offset, boolean x);
401
402 /** @see #getInt(Object, long) */
403 @IntrinsicCandidate
404 public native byte getByte(Object o, long offset);
405
406 /** @see #putInt(Object, long, int) */
407 @IntrinsicCandidate
408 public native void putByte(Object o, long offset, byte x);
409
410 /** @see #getInt(Object, long) */
411 @IntrinsicCandidate
412 public native short getShort(Object o, long offset);
413
1363 }
1364
1365 /**
1366 * Ensures the given class has been initialized (see JVMS-5.5 for details).
1367 * This is often needed in conjunction with obtaining the static field base
1368 * of a class.
1369 *
1370 * The call returns when either class {@code c} is fully initialized or
1371 * class {@code c} is being initialized and the call is performed from
1372 * the initializing thread. In the latter case a subsequent call to
1373 * {@link #shouldBeInitialized} will return {@code true}.
1374 */
1375 public void ensureClassInitialized(Class<?> c) {
1376 if (c == null) {
1377 throw new NullPointerException();
1378 }
1379
1380 ensureClassInitialized0(c);
1381 }
1382
1383 /**
1384 * The reading or writing of strict static fields may require
1385 * special processing. Notify the VM that such an event is about
1386 * to happen. The VM may respond by throwing an exception, in the
1387 * case of a read of an uninitialized field. If the VM allows the
1388 * method to return normally, no further calls are needed, with
1389 * the same arguments.
1390 */
1391 public void notifyStrictStaticAccess(Class<?> c, long staticFieldOffset, boolean writing) {
1392 if (c == null) {
1393 throw new NullPointerException();
1394 }
1395 notifyStrictStaticAccess0(c, staticFieldOffset, writing);
1396 }
1397
1398 /**
1399 * Reports the offset of the first element in the storage allocation of a
1400 * given array class. If {@link #arrayIndexScale} returns a non-zero value
1401 * for the same class, you may use that scale factor, together with this
1402 * base offset, to form new offsets to access elements of arrays of the
1403 * given class.
1404 * <p>
1405 * The return value is in the range of a {@code int}. The return type is
1406 * {@code long} to emphasize that long arithmetic should always be used
1407 * for offset calculations to avoid overflows.
1408 * <p>
1409 * This method doesn't support arrays with an element type that is
1410 * a value class, because this type of array can have multiple layouts.
1411 * For these arrays, {@code arrayInstanceBaseOffset(Object[] array)}
1412 * must be used instead.
1413 *
1414 * @see #getInt(Object, long)
1415 * @see #putInt(Object, long, int)
1416 */
1417 public long arrayBaseOffset(Class<?> arrayClass) {
1418 if (arrayClass == null) {
1419 throw new NullPointerException();
1420 }
1421
1422 return arrayBaseOffset0(arrayClass);
1423 }
1424
1425 public long arrayInstanceBaseOffset(Object[] array) {
1426 if (array == null) {
1427 throw new NullPointerException();
1428 }
1429
1430 return arrayInstanceBaseOffset0(array);
1431 }
1432
1433 /** The value of {@code arrayBaseOffset(boolean[].class)} */
1434 public static final long ARRAY_BOOLEAN_BASE_OFFSET
1435 = theUnsafe.arrayBaseOffset(boolean[].class);
1436
1437 /** The value of {@code arrayBaseOffset(byte[].class)} */
1438 public static final long ARRAY_BYTE_BASE_OFFSET
1439 = theUnsafe.arrayBaseOffset(byte[].class);
1440
1441 /** The value of {@code arrayBaseOffset(short[].class)} */
1442 public static final long ARRAY_SHORT_BASE_OFFSET
1443 = theUnsafe.arrayBaseOffset(short[].class);
1444
1445 /** The value of {@code arrayBaseOffset(char[].class)} */
1446 public static final long ARRAY_CHAR_BASE_OFFSET
1447 = theUnsafe.arrayBaseOffset(char[].class);
1448
1449 /** The value of {@code arrayBaseOffset(int[].class)} */
1450 public static final long ARRAY_INT_BASE_OFFSET
1451 = theUnsafe.arrayBaseOffset(int[].class);
1458 public static final long ARRAY_FLOAT_BASE_OFFSET
1459 = theUnsafe.arrayBaseOffset(float[].class);
1460
1461 /** The value of {@code arrayBaseOffset(double[].class)} */
1462 public static final long ARRAY_DOUBLE_BASE_OFFSET
1463 = theUnsafe.arrayBaseOffset(double[].class);
1464
1465 /** The value of {@code arrayBaseOffset(Object[].class)} */
1466 public static final long ARRAY_OBJECT_BASE_OFFSET
1467 = theUnsafe.arrayBaseOffset(Object[].class);
1468
1469 /**
1470 * Reports the scale factor for addressing elements in the storage
1471 * allocation of a given array class. However, arrays of "narrow" types
1472 * will generally not work properly with accessors like {@link
1473 * #getByte(Object, long)}, so the scale factor for such classes is reported
1474 * as zero.
1475 * <p>
1476 * The computation of the actual memory offset should always use {@code
1477 * long} arithmetic to avoid overflows.
1478 * <p>
1479 * This method doesn't support arrays with an element type that is
1480 * a value class, because this type of array can have multiple layouts.
1481 * For these arrays, {@code arrayInstanceIndexScale(Object[] array)}
1482 * must be used instead.
1483 *
1484 * @see #arrayBaseOffset
1485 * @see #getInt(Object, long)
1486 * @see #putInt(Object, long, int)
1487 */
1488 public int arrayIndexScale(Class<?> arrayClass) {
1489 if (arrayClass == null) {
1490 throw new NullPointerException();
1491 }
1492
1493 return arrayIndexScale0(arrayClass);
1494 }
1495
1496 public int arrayInstanceIndexScale(Object[] array) {
1497 if (array == null) {
1498 throw new NullPointerException();
1499 }
1500
1501 return arrayInstanceIndexScale0(array);
1502 }
1503
1504 /**
1505 * Returns the acmp map of this class, which must be a concrete value class.
1506 * Intended to be used by substitutability test in ValueObjectMethods only.
1507 * The format is subject to change.
1508 */
1509 public int[] getFieldMap(Class<?> c) {
1510 if (c == null) {
1511 throw new NullPointerException();
1512 }
1513 return getFieldMap0(c);
1514 }
1515
1516 /**
1517 * For a field of type {@code c}, returns true if and only if there is
1518 * a possible flat layout that contains no oop.
1519 * Required for numerical CAS safety.
1520 */
1521 public boolean isFlatPayloadBinary(Class<?> c) {
1522 int[] map = getFieldMap(c);
1523 int nbNonRef = map[0];
1524 return nbNonRef * 2 + 1 == map.length;
1525 }
1526
1527 /**
1528 * Return the size of the object in the heap.
1529 * @param o an object
1530 * @return the objects's size
1531 * @since Valhalla
1532 */
1533 public long getObjectSize(Object o) {
1534 if (o == null)
1535 throw new NullPointerException();
1536 return getObjectSize0(o);
1537 }
1538
1539 /** The value of {@code arrayIndexScale(boolean[].class)} */
1540 public static final int ARRAY_BOOLEAN_INDEX_SCALE
1541 = theUnsafe.arrayIndexScale(boolean[].class);
1542
1543 /** The value of {@code arrayIndexScale(byte[].class)} */
1544 public static final int ARRAY_BYTE_INDEX_SCALE
1545 = theUnsafe.arrayIndexScale(byte[].class);
1546
1547 /** The value of {@code arrayIndexScale(short[].class)} */
1548 public static final int ARRAY_SHORT_INDEX_SCALE
1549 = theUnsafe.arrayIndexScale(short[].class);
1550
1551 /** The value of {@code arrayIndexScale(char[].class)} */
1552 public static final int ARRAY_CHAR_INDEX_SCALE
1553 = theUnsafe.arrayIndexScale(char[].class);
1554
1555 /** The value of {@code arrayIndexScale(int[].class)} */
1556 public static final int ARRAY_INT_INDEX_SCALE
1557 = theUnsafe.arrayIndexScale(int[].class);
1621 public Class<?> defineClass(String name, byte[] b, int off, int len,
1622 ClassLoader loader,
1623 ProtectionDomain protectionDomain) {
1624 if (b == null) {
1625 throw new NullPointerException();
1626 }
1627 if (len < 0) {
1628 throw new ArrayIndexOutOfBoundsException();
1629 }
1630
1631 return defineClass0(name, b, off, len, loader, protectionDomain);
1632 }
1633
1634 public native Class<?> defineClass0(String name, byte[] b, int off, int len,
1635 ClassLoader loader,
1636 ProtectionDomain protectionDomain);
1637
1638 /**
1639 * Allocates an instance but does not run any constructor.
1640 * Initializes the class if it has not yet been.
1641 * <p>
1642 * This method returns an uninitialized instance. In general, this is undefined behavior, this
1643 * method is treated specially by the JVM to allow this behavior. The returned value must be
1644 * passed into a constructor using {@link MethodHandle#linkToSpecial} before any other
1645 * operation can be performed on it. Otherwise, the program is ill-formed.
1646 */
1647 @IntrinsicCandidate
1648 public native Object allocateInstance(Class<?> cls)
1649 throws InstantiationException;
1650
1651 /**
1652 * Allocates an array of a given type, but does not do zeroing.
1653 * <p>
1654 * This method should only be used in the very rare cases where a high-performance code
1655 * overwrites the destination array completely, and compilers cannot assist in zeroing elimination.
1656 * In an overwhelming majority of cases, a normal Java allocation should be used instead.
1657 * <p>
1658 * Users of this method are <b>required</b> to overwrite the initial (garbage) array contents
1659 * before allowing untrusted code, or code in other threads, to observe the reference
1660 * to the newly allocated array. In addition, the publication of the array reference must be
1661 * safe according to the Java Memory Model requirements.
1662 * <p>
1663 * The safest approach to deal with an uninitialized array is to keep the reference to it in local
1664 * variable at least until the initialization is complete, and then publish it <b>once</b>, either
1665 * by writing it to a <em>volatile</em> field, or storing it into a <em>final</em> field in constructor,
1701 return null;
1702 }
1703
1704 /** Throws the exception without telling the verifier. */
1705 public native void throwException(Throwable ee);
1706
1707 /**
1708 * Atomically updates Java variable to {@code x} if it is currently
1709 * holding {@code expected}.
1710 *
1711 * <p>This operation has memory semantics of a {@code volatile} read
1712 * and write. Corresponds to C11 atomic_compare_exchange_strong.
1713 *
1714 * @return {@code true} if successful
1715 */
1716 @IntrinsicCandidate
1717 public final native boolean compareAndSetReference(Object o, long offset,
1718 Object expected,
1719 Object x);
1720
1721 private final boolean isValueObject(Object o) {
1722 return o != null && o.getClass().isValue();
1723 }
1724
1725 /*
1726 * For value type, CAS should do substitutability test as opposed
1727 * to two pointers comparison.
1728 */
1729 @ForceInline
1730 public final <V> boolean compareAndSetReference(Object o, long offset,
1731 Class<?> type,
1732 V expected,
1733 V x) {
1734 if (isValueObject(expected)) {
1735 while (true) {
1736 Object witness = getReferenceVolatile(o, offset);
1737 if (witness != expected) {
1738 return false;
1739 }
1740 if (compareAndSetReference(o, offset, witness, x)) {
1741 return true;
1742 }
1743 }
1744 } else {
1745 return compareAndSetReference(o, offset, expected, x);
1746 }
1747 }
1748
1749 @ForceInline
1750 public final <V> boolean compareAndSetFlatValue(Object o, long offset,
1751 int layout,
1752 Class<?> valueType,
1753 V expected,
1754 V x) {
1755 Object[] array = newSpecialArray(valueType, 2, layout);
1756 return compareAndSetFlatValueAsBytes(array, o, offset, layout, valueType, expected, x);
1757 }
1758
1759 @IntrinsicCandidate
1760 public final native Object compareAndExchangeReference(Object o, long offset,
1761 Object expected,
1762 Object x);
1763
1764 @ForceInline
1765 public final <V> Object compareAndExchangeReference(Object o, long offset,
1766 Class<?> valueType,
1767 V expected,
1768 V x) {
1769 if (isValueObject(expected)) {
1770 while (true) {
1771 Object witness = getReferenceVolatile(o, offset);
1772 if (witness != expected) {
1773 return witness;
1774 }
1775 if (compareAndSetReference(o, offset, witness, x)) {
1776 return witness;
1777 }
1778 }
1779 } else {
1780 return compareAndExchangeReference(o, offset, expected, x);
1781 }
1782 }
1783
1784 @ForceInline
1785 public final <V> Object compareAndExchangeFlatValue(Object o, long offset,
1786 int layout,
1787 Class<?> valueType,
1788 V expected,
1789 V x) {
1790 Object[] array = newSpecialArray(valueType, 2, layout);
1791 compareAndSetFlatValueAsBytes(array, o, offset, layout, valueType, expected, x);
1792 return array[0];
1793 }
1794
1795 @IntrinsicCandidate
1796 public final Object compareAndExchangeReferenceAcquire(Object o, long offset,
1797 Object expected,
1798 Object x) {
1799 return compareAndExchangeReference(o, offset, expected, x);
1800 }
1801
1802 public final <V> Object compareAndExchangeReferenceAcquire(Object o, long offset,
1803 Class<?> valueType,
1804 V expected,
1805 V x) {
1806 return compareAndExchangeReference(o, offset, valueType, expected, x);
1807 }
1808
1809 @ForceInline
1810 public final <V> Object compareAndExchangeFlatValueAcquire(Object o, long offset,
1811 int layout,
1812 Class<?> valueType,
1813 V expected,
1814 V x) {
1815 return compareAndExchangeFlatValue(o, offset, layout, valueType, expected, x);
1816 }
1817
1818 @IntrinsicCandidate
1819 public final Object compareAndExchangeReferenceRelease(Object o, long offset,
1820 Object expected,
1821 Object x) {
1822 return compareAndExchangeReference(o, offset, expected, x);
1823 }
1824
1825 public final <V> Object compareAndExchangeReferenceRelease(Object o, long offset,
1826 Class<?> valueType,
1827 V expected,
1828 V x) {
1829 return compareAndExchangeReference(o, offset, valueType, expected, x);
1830 }
1831
1832 @ForceInline
1833 public final <V> Object compareAndExchangeFlatValueRelease(Object o, long offset,
1834 int layout,
1835 Class<?> valueType,
1836 V expected,
1837 V x) {
1838 return compareAndExchangeFlatValue(o, offset, layout, valueType, expected, x);
1839 }
1840
1841 @IntrinsicCandidate
1842 public final boolean weakCompareAndSetReferencePlain(Object o, long offset,
1843 Object expected,
1844 Object x) {
1845 return compareAndSetReference(o, offset, expected, x);
1846 }
1847
1848 public final <V> boolean weakCompareAndSetReferencePlain(Object o, long offset,
1849 Class<?> valueType,
1850 V expected,
1851 V x) {
1852 if (isValueObject(expected)) {
1853 return compareAndSetReference(o, offset, valueType, expected, x);
1854 } else {
1855 return weakCompareAndSetReferencePlain(o, offset, expected, x);
1856 }
1857 }
1858
1859 @ForceInline
1860 public final <V> boolean weakCompareAndSetFlatValuePlain(Object o, long offset,
1861 int layout,
1862 Class<?> valueType,
1863 V expected,
1864 V x) {
1865 return compareAndSetFlatValue(o, offset, layout, valueType, expected, x);
1866 }
1867
1868 @IntrinsicCandidate
1869 public final boolean weakCompareAndSetReferenceAcquire(Object o, long offset,
1870 Object expected,
1871 Object x) {
1872 return compareAndSetReference(o, offset, expected, x);
1873 }
1874
1875 public final <V> boolean weakCompareAndSetReferenceAcquire(Object o, long offset,
1876 Class<?> valueType,
1877 V expected,
1878 V x) {
1879 if (isValueObject(expected)) {
1880 return compareAndSetReference(o, offset, valueType, expected, x);
1881 } else {
1882 return weakCompareAndSetReferencePlain(o, offset, expected, x);
1883 }
1884 }
1885
1886 @ForceInline
1887 public final <V> boolean weakCompareAndSetFlatValueAcquire(Object o, long offset,
1888 int layout,
1889 Class<?> valueType,
1890 V expected,
1891 V x) {
1892 return compareAndSetFlatValue(o, offset, layout, valueType, expected, x);
1893 }
1894
1895 @IntrinsicCandidate
1896 public final boolean weakCompareAndSetReferenceRelease(Object o, long offset,
1897 Object expected,
1898 Object x) {
1899 return compareAndSetReference(o, offset, expected, x);
1900 }
1901
1902 public final <V> boolean weakCompareAndSetReferenceRelease(Object o, long offset,
1903 Class<?> valueType,
1904 V expected,
1905 V x) {
1906 if (isValueObject(expected)) {
1907 return compareAndSetReference(o, offset, valueType, expected, x);
1908 } else {
1909 return weakCompareAndSetReferencePlain(o, offset, expected, x);
1910 }
1911 }
1912
1913 @ForceInline
1914 public final <V> boolean weakCompareAndSetFlatValueRelease(Object o, long offset,
1915 int layout,
1916 Class<?> valueType,
1917 V expected,
1918 V x) {
1919 return compareAndSetFlatValue(o, offset, layout, valueType, expected, x);
1920 }
1921
1922 @IntrinsicCandidate
1923 public final boolean weakCompareAndSetReference(Object o, long offset,
1924 Object expected,
1925 Object x) {
1926 return compareAndSetReference(o, offset, expected, x);
1927 }
1928
1929 public final <V> boolean weakCompareAndSetReference(Object o, long offset,
1930 Class<?> valueType,
1931 V expected,
1932 V x) {
1933 if (isValueObject(expected)) {
1934 return compareAndSetReference(o, offset, valueType, expected, x);
1935 } else {
1936 return weakCompareAndSetReferencePlain(o, offset, expected, x);
1937 }
1938 }
1939
1940 @ForceInline
1941 public final <V> boolean weakCompareAndSetFlatValue(Object o, long offset,
1942 int layout,
1943 Class<?> valueType,
1944 V expected,
1945 V x) {
1946 return compareAndSetFlatValue(o, offset, layout, valueType, expected, x);
1947 }
1948
1949 /**
1950 * Atomically updates Java variable to {@code x} if it is currently
1951 * holding {@code expected}.
1952 *
1953 * <p>This operation has memory semantics of a {@code volatile} read
1954 * and write. Corresponds to C11 atomic_compare_exchange_strong.
1955 *
1956 * @return {@code true} if successful
1957 */
1958 @IntrinsicCandidate
1959 public final native boolean compareAndSetInt(Object o, long offset,
1960 int expected,
1961 int x);
1962
1963 @IntrinsicCandidate
1964 public final native int compareAndExchangeInt(Object o, long offset,
1965 int expected,
1966 int x);
1967
1968 @IntrinsicCandidate
2544 public final boolean weakCompareAndSetLongRelease(Object o, long offset,
2545 long expected,
2546 long x) {
2547 return compareAndSetLong(o, offset, expected, x);
2548 }
2549
2550 @IntrinsicCandidate
2551 public final boolean weakCompareAndSetLong(Object o, long offset,
2552 long expected,
2553 long x) {
2554 return compareAndSetLong(o, offset, expected, x);
2555 }
2556
2557 /**
2558 * Fetches a reference value from a given Java variable, with volatile
2559 * load semantics. Otherwise identical to {@link #getReference(Object, long)}
2560 */
2561 @IntrinsicCandidate
2562 public native Object getReferenceVolatile(Object o, long offset);
2563
2564 @ForceInline
2565 public final <V> Object getFlatValueVolatile(Object o, long offset, int layout, Class<?> valueType) {
2566 // we translate using fences (see: https://gee.cs.oswego.edu/dl/html/j9mm.html)
2567 Object res = getFlatValue(o, offset, layout, valueType);
2568 fullFence();
2569 return res;
2570 }
2571
2572 /**
2573 * Stores a reference value into a given Java variable, with
2574 * volatile store semantics. Otherwise identical to {@link #putReference(Object, long, Object)}
2575 */
2576 @IntrinsicCandidate
2577 public native void putReferenceVolatile(Object o, long offset, Object x);
2578
2579 @ForceInline
2580 public final <V> void putFlatValueVolatile(Object o, long offset, int layout, Class<?> valueType, V x) {
2581 // we translate using fences (see: https://gee.cs.oswego.edu/dl/html/j9mm.html)
2582 putFlatValueRelease(o, offset, layout, valueType, x);
2583 fullFence();
2584 }
2585
2586 /** Volatile version of {@link #getInt(Object, long)} */
2587 @IntrinsicCandidate
2588 public native int getIntVolatile(Object o, long offset);
2589
2590 /** Volatile version of {@link #putInt(Object, long, int)} */
2591 @IntrinsicCandidate
2592 public native void putIntVolatile(Object o, long offset, int x);
2593
2594 /** Volatile version of {@link #getBoolean(Object, long)} */
2595 @IntrinsicCandidate
2596 public native boolean getBooleanVolatile(Object o, long offset);
2597
2598 /** Volatile version of {@link #putBoolean(Object, long, boolean)} */
2599 @IntrinsicCandidate
2600 public native void putBooleanVolatile(Object o, long offset, boolean x);
2601
2602 /** Volatile version of {@link #getByte(Object, long)} */
2603 @IntrinsicCandidate
2604 public native byte getByteVolatile(Object o, long offset);
2605
2638 /** Volatile version of {@link #putFloat(Object, long, float)} */
2639 @IntrinsicCandidate
2640 public native void putFloatVolatile(Object o, long offset, float x);
2641
2642 /** Volatile version of {@link #getDouble(Object, long)} */
2643 @IntrinsicCandidate
2644 public native double getDoubleVolatile(Object o, long offset);
2645
2646 /** Volatile version of {@link #putDouble(Object, long, double)} */
2647 @IntrinsicCandidate
2648 public native void putDoubleVolatile(Object o, long offset, double x);
2649
2650
2651
2652 /** Acquire version of {@link #getReferenceVolatile(Object, long)} */
2653 @IntrinsicCandidate
2654 public final Object getReferenceAcquire(Object o, long offset) {
2655 return getReferenceVolatile(o, offset);
2656 }
2657
2658 @ForceInline
2659 public final <V> Object getFlatValueAcquire(Object o, long offset, int layout, Class<?> valueType) {
2660 // we translate using fences (see: https://gee.cs.oswego.edu/dl/html/j9mm.html)
2661 Object res = getFlatValue(o, offset, layout, valueType);
2662 loadFence();
2663 return res;
2664 }
2665
2666 /** Acquire version of {@link #getBooleanVolatile(Object, long)} */
2667 @IntrinsicCandidate
2668 public final boolean getBooleanAcquire(Object o, long offset) {
2669 return getBooleanVolatile(o, offset);
2670 }
2671
2672 /** Acquire version of {@link #getByteVolatile(Object, long)} */
2673 @IntrinsicCandidate
2674 public final byte getByteAcquire(Object o, long offset) {
2675 return getByteVolatile(o, offset);
2676 }
2677
2678 /** Acquire version of {@link #getShortVolatile(Object, long)} */
2679 @IntrinsicCandidate
2680 public final short getShortAcquire(Object o, long offset) {
2681 return getShortVolatile(o, offset);
2682 }
2683
2684 /** Acquire version of {@link #getCharVolatile(Object, long)} */
2685 @IntrinsicCandidate
2710 public final double getDoubleAcquire(Object o, long offset) {
2711 return getDoubleVolatile(o, offset);
2712 }
2713
2714 /*
2715 * Versions of {@link #putReferenceVolatile(Object, long, Object)}
2716 * that do not guarantee immediate visibility of the store to
2717 * other threads. This method is generally only useful if the
2718 * underlying field is a Java volatile (or if an array cell, one
2719 * that is otherwise only accessed using volatile accesses).
2720 *
2721 * Corresponds to C11 atomic_store_explicit(..., memory_order_release).
2722 */
2723
2724 /** Release version of {@link #putReferenceVolatile(Object, long, Object)} */
2725 @IntrinsicCandidate
2726 public final void putReferenceRelease(Object o, long offset, Object x) {
2727 putReferenceVolatile(o, offset, x);
2728 }
2729
2730 @ForceInline
2731 public final <V> void putFlatValueRelease(Object o, long offset, int layout, Class<?> valueType, V x) {
2732 // we translate using fences (see: https://gee.cs.oswego.edu/dl/html/j9mm.html)
2733 storeFence();
2734 putFlatValue(o, offset, layout, valueType, x);
2735 }
2736
2737 /** Release version of {@link #putBooleanVolatile(Object, long, boolean)} */
2738 @IntrinsicCandidate
2739 public final void putBooleanRelease(Object o, long offset, boolean x) {
2740 putBooleanVolatile(o, offset, x);
2741 }
2742
2743 /** Release version of {@link #putByteVolatile(Object, long, byte)} */
2744 @IntrinsicCandidate
2745 public final void putByteRelease(Object o, long offset, byte x) {
2746 putByteVolatile(o, offset, x);
2747 }
2748
2749 /** Release version of {@link #putShortVolatile(Object, long, short)} */
2750 @IntrinsicCandidate
2751 public final void putShortRelease(Object o, long offset, short x) {
2752 putShortVolatile(o, offset, x);
2753 }
2754
2755 /** Release version of {@link #putCharVolatile(Object, long, char)} */
2756 @IntrinsicCandidate
2773 /** Release version of {@link #putLongVolatile(Object, long, long)} */
2774 @IntrinsicCandidate
2775 public final void putLongRelease(Object o, long offset, long x) {
2776 putLongVolatile(o, offset, x);
2777 }
2778
2779 /** Release version of {@link #putDoubleVolatile(Object, long, double)} */
2780 @IntrinsicCandidate
2781 public final void putDoubleRelease(Object o, long offset, double x) {
2782 putDoubleVolatile(o, offset, x);
2783 }
2784
2785 // ------------------------------ Opaque --------------------------------------
2786
2787 /** Opaque version of {@link #getReferenceVolatile(Object, long)} */
2788 @IntrinsicCandidate
2789 public final Object getReferenceOpaque(Object o, long offset) {
2790 return getReferenceVolatile(o, offset);
2791 }
2792
2793 @ForceInline
2794 public final <V> Object getFlatValueOpaque(Object o, long offset, int layout, Class<?> valueType) {
2795 // this is stronger than opaque semantics
2796 return getFlatValueAcquire(o, offset, layout, valueType);
2797 }
2798
2799 /** Opaque version of {@link #getBooleanVolatile(Object, long)} */
2800 @IntrinsicCandidate
2801 public final boolean getBooleanOpaque(Object o, long offset) {
2802 return getBooleanVolatile(o, offset);
2803 }
2804
2805 /** Opaque version of {@link #getByteVolatile(Object, long)} */
2806 @IntrinsicCandidate
2807 public final byte getByteOpaque(Object o, long offset) {
2808 return getByteVolatile(o, offset);
2809 }
2810
2811 /** Opaque version of {@link #getShortVolatile(Object, long)} */
2812 @IntrinsicCandidate
2813 public final short getShortOpaque(Object o, long offset) {
2814 return getShortVolatile(o, offset);
2815 }
2816
2817 /** Opaque version of {@link #getCharVolatile(Object, long)} */
2818 @IntrinsicCandidate
2833 }
2834
2835 /** Opaque version of {@link #getLongVolatile(Object, long)} */
2836 @IntrinsicCandidate
2837 public final long getLongOpaque(Object o, long offset) {
2838 return getLongVolatile(o, offset);
2839 }
2840
2841 /** Opaque version of {@link #getDoubleVolatile(Object, long)} */
2842 @IntrinsicCandidate
2843 public final double getDoubleOpaque(Object o, long offset) {
2844 return getDoubleVolatile(o, offset);
2845 }
2846
2847 /** Opaque version of {@link #putReferenceVolatile(Object, long, Object)} */
2848 @IntrinsicCandidate
2849 public final void putReferenceOpaque(Object o, long offset, Object x) {
2850 putReferenceVolatile(o, offset, x);
2851 }
2852
2853 @ForceInline
2854 public final <V> void putFlatValueOpaque(Object o, long offset, int layout, Class<?> valueType, V x) {
2855 // this is stronger than opaque semantics
2856 putFlatValueRelease(o, offset, layout, valueType, x);
2857 }
2858
2859 /** Opaque version of {@link #putBooleanVolatile(Object, long, boolean)} */
2860 @IntrinsicCandidate
2861 public final void putBooleanOpaque(Object o, long offset, boolean x) {
2862 putBooleanVolatile(o, offset, x);
2863 }
2864
2865 /** Opaque version of {@link #putByteVolatile(Object, long, byte)} */
2866 @IntrinsicCandidate
2867 public final void putByteOpaque(Object o, long offset, byte x) {
2868 putByteVolatile(o, offset, x);
2869 }
2870
2871 /** Opaque version of {@link #putShortVolatile(Object, long, short)} */
2872 @IntrinsicCandidate
2873 public final void putShortOpaque(Object o, long offset, short x) {
2874 putShortVolatile(o, offset, x);
2875 }
2876
2877 /** Opaque version of {@link #putCharVolatile(Object, long, char)} */
2878 @IntrinsicCandidate
2887 }
2888
2889 /** Opaque version of {@link #putFloatVolatile(Object, long, float)} */
2890 @IntrinsicCandidate
2891 public final void putFloatOpaque(Object o, long offset, float x) {
2892 putFloatVolatile(o, offset, x);
2893 }
2894
2895 /** Opaque version of {@link #putLongVolatile(Object, long, long)} */
2896 @IntrinsicCandidate
2897 public final void putLongOpaque(Object o, long offset, long x) {
2898 putLongVolatile(o, offset, x);
2899 }
2900
2901 /** Opaque version of {@link #putDoubleVolatile(Object, long, double)} */
2902 @IntrinsicCandidate
2903 public final void putDoubleOpaque(Object o, long offset, double x) {
2904 putDoubleVolatile(o, offset, x);
2905 }
2906
2907 @ForceInline
2908 private boolean compareAndSetFlatValueAsBytes(Object[] array, Object o, long offset, int layout, Class<?> valueType, Object expected, Object x) {
2909 // We can convert between a value object and a binary value (of suitable size) using array elements.
2910 // This only works if the payload contains no oops (see VarHandles::isAtomicFlat).
2911 // Thus, we can implement the CAS with a plain numeric CAS.
2912
2913 // array[0]: witness (put as binary, get as object), at base
2914 // array[1]: x (put as object, get as binary), at base + scale
2915 // When witness == expected, the witness binary may be different from the expected binary.
2916 // This happens when compiler does not zero unused positions in the witness.
2917 // So we must obtain the witness binary and use it as expected binary for the numeric CAS.
2918 long base = arrayInstanceBaseOffset(array);
2919 int scale = arrayInstanceIndexScale(array);
2920 putFlatValue(array, base + scale, layout, valueType, x); // put x as object
2921 switch (scale) {
2922 case 1: {
2923 do {
2924 byte witnessByte = getByteVolatile(o, offset);
2925 putByte(array, base, witnessByte); // put witness as binary
2926 Object witness = getFlatValue(array, base, layout, valueType); // get witness as object
2927 if (witness != expected) {
2928 return false;
2929 }
2930 byte xByte = getByte(array, base + scale); // get x as binary
2931 if (compareAndSetByte(o, offset, witnessByte, xByte)) {
2932 return true;
2933 }
2934 } while (true);
2935 }
2936 case 2: {
2937 do {
2938 short witnessShort = getShortVolatile(o, offset);
2939 putShort(array, base, witnessShort); // put witness as binary
2940 Object witness = getFlatValue(array, base, layout, valueType); // get witness as object
2941 if (witness != expected) {
2942 return false;
2943 }
2944 short xShort = getShort(array, base + scale); // get x as binary
2945 if (compareAndSetShort(o, offset, witnessShort, xShort)) {
2946 return true;
2947 }
2948 } while (true);
2949 }
2950 case 4: {
2951 do {
2952 int witnessInt = getIntVolatile(o, offset);
2953 putInt(array, base, witnessInt); // put witness as binary
2954 Object witness = getFlatValue(array, base, layout, valueType); // get witness as object
2955 if (witness != expected) {
2956 return false;
2957 }
2958 int xInt = getInt(array, base + scale); // get x as binary
2959 if (compareAndSetInt(o, offset, witnessInt, xInt)) {
2960 return true;
2961 }
2962 } while (true);
2963 }
2964 case 8: {
2965 do {
2966 long witnessLong = getLongVolatile(o, offset);
2967 putLong(array, base, witnessLong); // put witness as binary
2968 Object witness = getFlatValue(array, base, layout, valueType);
2969 if (witness != expected) {
2970 return false;
2971 }
2972 long xLong = getLong(array, base + scale); // get x as binary
2973 if (compareAndSetLong(o, offset, witnessLong, xLong)) {
2974 return true;
2975 }
2976 } while (true);
2977 }
2978 default: {
2979 throw new UnsupportedOperationException();
2980 }
2981 }
2982 }
2983
2984 /**
2985 * Unblocks the given thread blocked on {@code park}, or, if it is
2986 * not blocked, causes the subsequent call to {@code park} not to
2987 * block. Note: this operation is "unsafe" solely because the
2988 * caller must somehow ensure that the thread has not been
2989 * destroyed. Nothing special is usually required to ensure this
2990 * when called from Java (in which there will ordinarily be a live
2991 * reference to the thread) but this is not nearly-automatically
2992 * so when calling from native code.
2993 *
2994 * @param thread the thread to unpark.
2995 */
2996 @IntrinsicCandidate
2997 public native void unpark(Object thread);
2998
2999 /**
3000 * Blocks current thread, returning when a balancing
3001 * {@code unpark} occurs, or a balancing {@code unpark} has
3002 * already occurred, or the thread is interrupted, or, if not
3003 * absolute and time is not zero, the given time nanoseconds have
3350 /**
3351 * Atomically exchanges the given reference value with the current
3352 * reference value of a field or array element within the given
3353 * object {@code o} at the given {@code offset}.
3354 *
3355 * @param o object/array to update the field/element in
3356 * @param offset field/element offset
3357 * @param newValue new value
3358 * @return the previous value
3359 * @since 1.8
3360 */
3361 @IntrinsicCandidate
3362 public final Object getAndSetReference(Object o, long offset, Object newValue) {
3363 Object v;
3364 do {
3365 v = getReferenceVolatile(o, offset);
3366 } while (!weakCompareAndSetReference(o, offset, v, newValue));
3367 return v;
3368 }
3369
3370 @ForceInline
3371 public final Object getAndSetReference(Object o, long offset, Class<?> valueType, Object newValue) {
3372 Object v;
3373 do {
3374 v = getReferenceVolatile(o, offset);
3375 } while (!compareAndSetReference(o, offset, valueType, v, newValue));
3376 return v;
3377 }
3378
3379 @ForceInline
3380 public Object getAndSetFlatValue(Object o, long offset, int layoutKind, Class<?> valueType, Object newValue) {
3381 Object v;
3382 do {
3383 v = getFlatValueVolatile(o, offset, layoutKind, valueType);
3384 } while (!compareAndSetFlatValue(o, offset, layoutKind, valueType, v, newValue));
3385 return v;
3386 }
3387
3388 @ForceInline
3389 public final Object getAndSetReferenceRelease(Object o, long offset, Object newValue) {
3390 Object v;
3391 do {
3392 v = getReference(o, offset);
3393 } while (!weakCompareAndSetReferenceRelease(o, offset, v, newValue));
3394 return v;
3395 }
3396
3397 @ForceInline
3398 public final Object getAndSetReferenceRelease(Object o, long offset, Class<?> valueType, Object newValue) {
3399 return getAndSetReference(o, offset, valueType, newValue);
3400 }
3401
3402 @ForceInline
3403 public Object getAndSetFlatValueRelease(Object o, long offset, int layoutKind, Class<?> valueType, Object x) {
3404 return getAndSetFlatValue(o, offset, layoutKind, valueType, x);
3405 }
3406
3407 @ForceInline
3408 public final Object getAndSetReferenceAcquire(Object o, long offset, Object newValue) {
3409 Object v;
3410 do {
3411 v = getReferenceAcquire(o, offset);
3412 } while (!weakCompareAndSetReferenceAcquire(o, offset, v, newValue));
3413 return v;
3414 }
3415
3416 @ForceInline
3417 public final Object getAndSetReferenceAcquire(Object o, long offset, Class<?> valueType, Object newValue) {
3418 return getAndSetReference(o, offset, valueType, newValue);
3419 }
3420
3421 @ForceInline
3422 public Object getAndSetFlatValueAcquire(Object o, long offset, int layoutKind, Class<?> valueType, Object x) {
3423 return getAndSetFlatValue(o, offset, layoutKind, valueType, x);
3424 }
3425
3426 @IntrinsicCandidate
3427 public final byte getAndSetByte(Object o, long offset, byte newValue) {
3428 byte v;
3429 do {
3430 v = getByteVolatile(o, offset);
3431 } while (!weakCompareAndSetByte(o, offset, v, newValue));
3432 return v;
3433 }
3434
3435 @ForceInline
3436 public final byte getAndSetByteRelease(Object o, long offset, byte newValue) {
3437 byte v;
3438 do {
3439 v = getByte(o, offset);
3440 } while (!weakCompareAndSetByteRelease(o, offset, v, newValue));
3441 return v;
3442 }
3443
3444 @ForceInline
3445 public final byte getAndSetByteAcquire(Object o, long offset, byte newValue) {
4461 private static short convEndian(boolean big, short n) { return big == BIG_ENDIAN ? n : Short.reverseBytes(n) ; }
4462 private static int convEndian(boolean big, int n) { return big == BIG_ENDIAN ? n : Integer.reverseBytes(n) ; }
4463 private static long convEndian(boolean big, long n) { return big == BIG_ENDIAN ? n : Long.reverseBytes(n) ; }
4464
4465
4466
4467 private native long allocateMemory0(long bytes);
4468 private native long reallocateMemory0(long address, long bytes);
4469 private native void freeMemory0(long address);
4470 @IntrinsicCandidate
4471 private native void setMemory0(Object o, long offset, long bytes, byte value);
4472 @IntrinsicCandidate
4473 private native void copyMemory0(Object srcBase, long srcOffset, Object destBase, long destOffset, long bytes);
4474 private native void copySwapMemory0(Object srcBase, long srcOffset, Object destBase, long destOffset, long bytes, long elemSize);
4475 private native long objectFieldOffset0(Field f); // throws IAE
4476 private native long knownObjectFieldOffset0(Class<?> c, String name); // error code: -1 not found, -2 static
4477 private native long staticFieldOffset0(Field f); // throws IAE
4478 private native Object staticFieldBase0(Field f); // throws IAE
4479 private native boolean shouldBeInitialized0(Class<?> c);
4480 private native void ensureClassInitialized0(Class<?> c);
4481 private native void notifyStrictStaticAccess0(Class<?> c, long staticFieldOffset, boolean writing);
4482 private native int arrayBaseOffset0(Class<?> arrayClass); // public version returns long to promote correct arithmetic
4483 @IntrinsicCandidate
4484 private native int arrayInstanceBaseOffset0(Object[] array);
4485 private native int arrayIndexScale0(Class<?> arrayClass);
4486 @IntrinsicCandidate
4487 private native int arrayInstanceIndexScale0(Object[] array);
4488 private native long getObjectSize0(Object o);
4489 private native int getLoadAverage0(double[] loadavg, int nelems);
4490 @IntrinsicCandidate
4491 private native int[] getFieldMap0(Class <?> c);
4492
4493
4494 /**
4495 * Invokes the given direct byte buffer's cleaner, if any.
4496 *
4497 * @param directBuffer a direct byte buffer
4498 * @throws NullPointerException if {@code directBuffer} is null
4499 * @throws IllegalArgumentException if {@code directBuffer} is non-direct,
4500 * or is a {@link java.nio.Buffer#slice slice}, or is a
4501 * {@link java.nio.Buffer#duplicate duplicate}
4502 */
4503 public void invokeCleaner(java.nio.ByteBuffer directBuffer) {
4504 if (!directBuffer.isDirect())
4505 throw new IllegalArgumentException("buffer is non-direct");
4506
4507 DirectBuffer db = (DirectBuffer) directBuffer;
4508 if (db.attachment() != null)
4509 throw new IllegalArgumentException("duplicate or slice");
4510
4511 Cleaner cleaner = db.cleaner();
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