1 /*
2 * Copyright (c) 2017, 2023, 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 package sun.nio.ch;
26
27 import java.io.IOException;
28 import java.util.Arrays;
29 import java.util.Map;
30 import java.util.concurrent.ConcurrentHashMap;
31 import java.util.concurrent.Executor;
32 import java.util.concurrent.Executors;
33 import java.util.concurrent.ThreadFactory;
34 import java.util.concurrent.locks.LockSupport;
35 import java.util.function.BooleanSupplier;
36 import jdk.internal.misc.InnocuousThread;
37 import sun.security.action.GetPropertyAction;
38
39 /**
40 * Polls file descriptors. Virtual threads invoke the poll method to park
41 * until a given file descriptor is ready for I/O.
42 */
43 abstract class Poller {
44 private static final Pollers POLLERS;
45 static {
46 try {
47 var pollers = new Pollers();
48 pollers.start();
49 POLLERS = pollers;
50 } catch (IOException ioe) {
51 throw new ExceptionInInitializerError(ioe);
52 }
53 }
54
55 // maps file descriptors to parked Thread
56 private final Map<Integer, Thread> map = new ConcurrentHashMap<>();
57
58 /**
59 * Poller mode.
60 */
61 enum Mode {
62 /**
63 * ReadPoller and WritePoller are dedicated platform threads that block waiting
64 * for events and unpark virtual threads when file descriptors are ready for I/O.
65 */
66 SYSTEM_THREADS,
67
68 /**
69 * ReadPoller and WritePoller threads are virtual threads that poll for events,
70 * yielding between polls and unparking virtual threads when file descriptors are
71 * ready for I/O. If there are no events then the poller threads park until there
72 * are I/O events to poll. This mode helps to integrate polling with virtual
73 * thread scheduling. The approach is similar to the default scheme in "User-level
74 * Threading: Have Your Cake and Eat It Too" by Karsten and Barghi 2020
75 * (https://dl.acm.org/doi/10.1145/3379483).
76 */
77 VTHREAD_POLLERS
78 }
79
80 /**
81 * Initialize a Poller.
82 */
83 protected Poller() {
84 }
85
86 /**
87 * Returns the poller's file descriptor, used when the read and write poller threads
88 * are virtual threads.
89 *
90 * @throws UnsupportedOperationException if not supported
91 */
92 int fdVal() {
93 throw new UnsupportedOperationException();
94 }
95
96 /**
97 * Register the file descriptor. The registration is "one shot", meaning it should
98 * be polled at most once.
99 */
100 abstract void implRegister(int fdVal) throws IOException;
101
102 /**
103 * Deregister the file descriptor.
104 * @param polled true if the file descriptor has already been polled
105 */
106 abstract void implDeregister(int fdVal, boolean polled);
107
108 /**
109 * Poll for events. The {@link #polled(int)} method is invoked for each
110 * polled file descriptor.
111 *
112 * @param timeout if positive then block for up to {@code timeout} milliseconds,
113 * if zero then don't block, if -1 then block indefinitely
114 * @return the number of file descriptors polled
115 */
116 abstract int poll(int timeout) throws IOException;
117
118 /**
119 * Callback by the poll method when a file descriptor is polled.
120 */
121 final void polled(int fdVal) {
122 wakeup(fdVal);
123 }
124
125 /**
126 * Parks the current thread until a file descriptor is ready for the given op.
127 * @param fdVal the file descriptor
128 * @param event POLLIN or POLLOUT
129 * @param nanos the waiting time or 0 to wait indefinitely
130 * @param supplier supplies a boolean to indicate if the enclosing object is open
131 */
132 static void poll(int fdVal, int event, long nanos, BooleanSupplier supplier)
133 throws IOException
134 {
135 assert nanos >= 0L;
136 if (event == Net.POLLIN) {
137 POLLERS.readPoller(fdVal).poll(fdVal, nanos, supplier);
138 } else if (event == Net.POLLOUT) {
139 POLLERS.writePoller(fdVal).poll(fdVal, nanos, supplier);
140 } else {
141 assert false;
142 }
143 }
144
145 /**
146 * If there is a thread polling the given file descriptor for the given event then
147 * the thread is unparked.
148 */
149 static void stopPoll(int fdVal, int event) {
150 if (event == Net.POLLIN) {
151 POLLERS.readPoller(fdVal).wakeup(fdVal);
152 } else if (event == Net.POLLOUT) {
153 POLLERS.writePoller(fdVal).wakeup(fdVal);
154 } else {
155 throw new IllegalArgumentException();
156 }
157 }
158
159 /**
160 * If there are any threads polling the given file descriptor then they are unparked.
161 */
162 static void stopPoll(int fdVal) {
163 stopPoll(fdVal, Net.POLLIN);
164 stopPoll(fdVal, Net.POLLOUT);
165 }
166
167 /**
168 * Parks the current thread until a file descriptor is ready.
169 */
170 private void poll(int fdVal, long nanos, BooleanSupplier supplier) throws IOException {
171 register(fdVal);
172 try {
173 boolean isOpen = supplier.getAsBoolean();
174 if (isOpen) {
175 if (nanos > 0) {
176 LockSupport.parkNanos(nanos);
177 } else {
178 LockSupport.park();
179 }
180 }
181 } finally {
182 deregister(fdVal);
183 }
184 }
185
186 /**
187 * Registers the file descriptor to be polled at most once when the file descriptor
188 * is ready for I/O.
189 */
190 private void register(int fdVal) throws IOException {
191 Thread previous = map.put(fdVal, Thread.currentThread());
192 assert previous == null;
193 implRegister(fdVal);
194 }
195
196 /**
197 * Deregister the file descriptor so that the file descriptor is not polled.
198 */
199 private void deregister(int fdVal) {
200 Thread previous = map.remove(fdVal);
201 boolean polled = (previous == null);
202 assert polled || previous == Thread.currentThread();
203 implDeregister(fdVal, polled);
204 }
205
206 /**
207 * Unparks any thread that is polling the given file descriptor.
208 */
209 private void wakeup(int fdVal) {
210 Thread t = map.remove(fdVal);
211 if (t != null) {
212 LockSupport.unpark(t);
213 }
214 }
215
216 /**
217 * Master polling loop. The {@link #polled(int)} method is invoked for each file
218 * descriptor that is polled.
219 */
220 private void pollerLoop() {
221 try {
222 for (;;) {
223 poll(-1);
224 }
225 } catch (Exception e) {
226 e.printStackTrace();
227 }
228 }
229
230 /**
231 * Sub-poller polling loop. The {@link #polled(int)} method is invoked for each file
232 * descriptor that is polled.
233 *
234 * The sub-poller registers its file descriptor with the master poller to park until
235 * there are events to poll. When unparked, it does non-blocking polls and parks
236 * again when there are no more events. The sub-poller yields after each poll to help
237 * with fairness and to avoid re-registering with the master poller where possible.
238 */
239 private void subPollerLoop(Poller masterPoller) {
240 assert Thread.currentThread().isVirtual();
241 try {
242 int polled = 0;
243 for (;;) {
244 if (polled == 0) {
245 masterPoller.poll(fdVal(), 0, () -> true); // park
246 } else {
247 Thread.yield();
248 }
249 polled = poll(0);
250 }
251 } catch (Exception e) {
252 e.printStackTrace();
253 }
254 }
255
256 /**
257 * The Pollers used for read and write events.
258 */
259 private static class Pollers {
260 private final PollerProvider provider;
261 private final Poller.Mode pollerMode;
262 private final Poller masterPoller;
263 private final Poller[] readPollers;
264 private final Poller[] writePollers;
265
266 // used by start method to executor is kept alive
267 private Executor executor;
268
269 /**
270 * Creates the Poller instances based on configuration.
271 */
272 Pollers() throws IOException {
273 PollerProvider provider = PollerProvider.provider();
274 Poller.Mode mode;
275 String s = GetPropertyAction.privilegedGetProperty("jdk.pollerMode");
276 if (s != null) {
277 if (s.equalsIgnoreCase(Mode.SYSTEM_THREADS.name()) || s.equals("1")) {
278 mode = Mode.SYSTEM_THREADS;
279 } else if (s.equalsIgnoreCase(Mode.VTHREAD_POLLERS.name()) || s.equals("2")) {
280 mode = Mode.VTHREAD_POLLERS;
281 } else {
282 throw new RuntimeException("Can't parse '" + s + "' as polling mode");
283 }
284 } else {
285 mode = provider.defaultPollerMode();
286 }
287
288 // vthread poller mode needs a master poller
289 Poller masterPoller = (mode == Mode.VTHREAD_POLLERS)
290 ? provider.readPoller(false)
291 : null;
292
293 // read pollers (or sub-pollers)
294 int readPollerCount = pollerCount("jdk.readPollers", provider.defaultReadPollers(mode));
295 Poller[] readPollers = new Poller[readPollerCount];
296 for (int i = 0; i < readPollerCount; i++) {
297 readPollers[i] = provider.readPoller(mode == Mode.VTHREAD_POLLERS);
298 }
299
300 // write pollers (or sub-pollers)
301 int writePollerCount = pollerCount("jdk.writePollers", provider.defaultWritePollers(mode));
302 Poller[] writePollers = new Poller[writePollerCount];
303 for (int i = 0; i < writePollerCount; i++) {
304 writePollers[i] = provider.writePoller(mode == Mode.VTHREAD_POLLERS);
305 }
306
307 this.provider = provider;
308 this.pollerMode = mode;
309 this.masterPoller = masterPoller;
310 this.readPollers = readPollers;
311 this.writePollers = writePollers;
312 }
313
314 /**
315 * Starts the Poller threads.
316 */
317 void start() {
318 if (pollerMode == Mode.VTHREAD_POLLERS) {
319 startPlatformThread("MasterPoller", masterPoller::pollerLoop);
320 ThreadFactory factory = Thread.ofVirtual()
321 .inheritInheritableThreadLocals(false)
322 .name("SubPoller-", 0)
323 .uncaughtExceptionHandler((t, e) -> e.printStackTrace())
324 .factory();
325 executor = Executors.newThreadPerTaskExecutor(factory);
326 Arrays.stream(readPollers).forEach(p -> {
327 executor.execute(() -> p.subPollerLoop(masterPoller));
328 });
329 Arrays.stream(writePollers).forEach(p -> {
330 executor.execute(() -> p.subPollerLoop(masterPoller));
331 });
332 } else {
333 Arrays.stream(readPollers).forEach(p -> {
334 startPlatformThread("Read-Poller", p::pollerLoop);
335 });
336 Arrays.stream(writePollers).forEach(p -> {
337 startPlatformThread("Write-Poller", p::pollerLoop);
338 });
339 }
340 }
341
342 /**
343 * Returns the read poller for the given file descriptor.
344 */
345 Poller readPoller(int fdVal) {
346 int index = provider.fdValToIndex(fdVal, readPollers.length);
347 return readPollers[index];
348 }
349
350 /**
351 * Returns the write poller for the given file descriptor.
352 */
353 Poller writePoller(int fdVal) {
354 int index = provider.fdValToIndex(fdVal, writePollers.length);
355 return writePollers[index];
356 }
357
358 /**
359 * Reads the given property name to get the poller count. If the property is
360 * set then the value must be a power of 2. Returns 1 if the property is not
361 * set.
362 * @throws IllegalArgumentException if the property is set to a value that
363 * is not a power of 2.
364 */
365 private static int pollerCount(String propName, int defaultCount) {
366 String s = GetPropertyAction.privilegedGetProperty(propName);
367 int count = (s != null) ? Integer.parseInt(s) : defaultCount;
368
369 // check power of 2
370 if (count != Integer.highestOneBit(count)) {
371 String msg = propName + " is set to a value that is not a power of 2";
372 throw new IllegalArgumentException(msg);
373 }
374 return count;
375 }
376
377 /**
378 * Starts a platform thread to run the given task.
379 */
380 private void startPlatformThread(String name, Runnable task) {
381 try {
382 Thread thread = InnocuousThread.newSystemThread(name, task);
383 thread.setDaemon(true);
384 thread.setUncaughtExceptionHandler((t, e) -> e.printStackTrace());
385 thread.start();
386 } catch (Exception e) {
387 throw new InternalError(e);
388 }
389 }
390 }
391 }