1 /* 2 * Copyright (c) 1998, 2024, 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. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #ifndef SHARE_RUNTIME_OBJECTMONITOR_HPP 26 #define SHARE_RUNTIME_OBJECTMONITOR_HPP 27 28 #include "memory/allocation.hpp" 29 #include "memory/padded.hpp" 30 #include "oops/markWord.hpp" 31 #include "oops/weakHandle.hpp" 32 #include "runtime/perfDataTypes.hpp" 33 34 class ObjectMonitor; 35 class ParkEvent; 36 37 // ObjectWaiter serves as a "proxy" or surrogate thread. 38 // TODO-FIXME: Eliminate ObjectWaiter and use the thread-specific 39 // ParkEvent instead. Beware, however, that the JVMTI code 40 // knows about ObjectWaiters, so we'll have to reconcile that code. 41 // See next_waiter(), first_waiter(), etc. 42 43 class ObjectWaiter : public StackObj { 44 public: 45 enum TStates { TS_UNDEF, TS_READY, TS_RUN, TS_WAIT, TS_ENTER, TS_CXQ }; 46 ObjectWaiter* volatile _next; 47 ObjectWaiter* volatile _prev; 48 JavaThread* _thread; 49 uint64_t _notifier_tid; 50 ParkEvent * _event; 51 volatile int _notified; 52 volatile TStates TState; 53 bool _active; // Contention monitoring is enabled 54 public: 55 ObjectWaiter(JavaThread* current); 56 57 void wait_reenter_begin(ObjectMonitor *mon); 58 void wait_reenter_end(ObjectMonitor *mon); 59 }; 60 61 // The ObjectMonitor class implements the heavyweight version of a 62 // JavaMonitor. The lightweight BasicLock/stack lock version has been 63 // inflated into an ObjectMonitor. This inflation is typically due to 64 // contention or use of Object.wait(). 65 // 66 // WARNING: This is a very sensitive and fragile class. DO NOT make any 67 // changes unless you are fully aware of the underlying semantics. 68 // 69 // ObjectMonitor Layout Overview/Highlights/Restrictions: 70 // 71 // - The _header field must be at offset 0 because the displaced header 72 // from markWord is stored there. We do not want markWord.hpp to include 73 // ObjectMonitor.hpp to avoid exposing ObjectMonitor everywhere. This 74 // means that ObjectMonitor cannot inherit from any other class nor can 75 // it use any virtual member functions. This restriction is critical to 76 // the proper functioning of the VM. 77 // - The _header and _owner fields should be separated by enough space 78 // to avoid false sharing due to parallel access by different threads. 79 // This is an advisory recommendation. 80 // - The general layout of the fields in ObjectMonitor is: 81 // _header 82 // <lightly_used_fields> 83 // <optional padding> 84 // _owner 85 // <remaining_fields> 86 // - The VM assumes write ordering and machine word alignment with 87 // respect to the _owner field and the <remaining_fields> that can 88 // be read in parallel by other threads. 89 // - Generally fields that are accessed closely together in time should 90 // be placed proximally in space to promote data cache locality. That 91 // is, temporal locality should condition spatial locality. 92 // - We have to balance avoiding false sharing with excessive invalidation 93 // from coherence traffic. As such, we try to cluster fields that tend 94 // to be _written_ at approximately the same time onto the same data 95 // cache line. 96 // - We also have to balance the natural tension between minimizing 97 // single threaded capacity misses with excessive multi-threaded 98 // coherency misses. There is no single optimal layout for both 99 // single-threaded and multi-threaded environments. 100 // 101 // - See TEST_VM(ObjectMonitor, sanity) gtest for how critical restrictions are 102 // enforced. 103 // - Adjacent ObjectMonitors should be separated by enough space to avoid 104 // false sharing. This is handled by the ObjectMonitor allocation code 105 // in synchronizer.cpp. Also see TEST_VM(SynchronizerTest, sanity) gtest. 106 // 107 // Futures notes: 108 // - Separating _owner from the <remaining_fields> by enough space to 109 // avoid false sharing might be profitable. Given 110 // http://blogs.oracle.com/dave/entry/cas_and_cache_trivia_invalidate 111 // we know that the CAS in monitorenter will invalidate the line 112 // underlying _owner. We want to avoid an L1 data cache miss on that 113 // same line for monitorexit. Putting these <remaining_fields>: 114 // _recursions, _EntryList, _cxq, and _succ, all of which may be 115 // fetched in the inflated unlock path, on a different cache line 116 // would make them immune to CAS-based invalidation from the _owner 117 // field. 118 // 119 // - The _recursions field should be of type int, or int32_t but not 120 // intptr_t. There's no reason to use a 64-bit type for this field 121 // in a 64-bit JVM. 122 123 #ifndef OM_CACHE_LINE_SIZE 124 // Use DEFAULT_CACHE_LINE_SIZE if not already specified for 125 // the current build platform. 126 #define OM_CACHE_LINE_SIZE DEFAULT_CACHE_LINE_SIZE 127 #endif 128 129 class ObjectMonitor : public CHeapObj<mtObjectMonitor> { 130 friend class ObjectSynchronizer; 131 friend class ObjectWaiter; 132 friend class VMStructs; 133 JVMCI_ONLY(friend class JVMCIVMStructs;) 134 135 static OopStorage* _oop_storage; 136 137 // The sync code expects the header field to be at offset zero (0). 138 // Enforced by the assert() in header_addr(). 139 volatile markWord _header; // displaced object header word - mark 140 WeakHandle _object; // backward object pointer 141 // Separate _header and _owner on different cache lines since both can 142 // have busy multi-threaded access. _header and _object are set at initial 143 // inflation. The _object does not change, so it is a good choice to share 144 // its cache line with _header. 145 DEFINE_PAD_MINUS_SIZE(0, OM_CACHE_LINE_SIZE, sizeof(volatile markWord) + 146 sizeof(WeakHandle)); 147 // Used by async deflation as a marker in the _owner field. 148 // Note that the choice of the two markers is peculiar: 149 // - They need to represent values that cannot be pointers. In particular, 150 // we achieve this by using the lowest two bits. 151 // - ANONYMOUS_OWNER should be a small value, it is used in generated code 152 // and small values encode much better. 153 // - We test for anonymous owner by testing for the lowest bit, therefore 154 // DEFLATER_MARKER must *not* have that bit set. 155 #define DEFLATER_MARKER reinterpret_cast<void*>(2) 156 public: 157 // NOTE: Typed as uintptr_t so that we can pick it up in SA, via vmStructs. 158 static const uintptr_t ANONYMOUS_OWNER = 1; 159 160 private: 161 static void* anon_owner_ptr() { return reinterpret_cast<void*>(ANONYMOUS_OWNER); } 162 163 void* volatile _owner; // pointer to owning thread OR BasicLock 164 volatile uint64_t _previous_owner_tid; // thread id of the previous owner of the monitor 165 // Separate _owner and _next_om on different cache lines since 166 // both can have busy multi-threaded access. _previous_owner_tid is only 167 // changed by ObjectMonitor::exit() so it is a good choice to share the 168 // cache line with _owner. 169 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(void* volatile) + 170 sizeof(volatile uint64_t)); 171 ObjectMonitor* _next_om; // Next ObjectMonitor* linkage 172 volatile intx _recursions; // recursion count, 0 for first entry 173 ObjectWaiter* volatile _EntryList; // Threads blocked on entry or reentry. 174 // The list is actually composed of WaitNodes, 175 // acting as proxies for Threads. 176 177 ObjectWaiter* volatile _cxq; // LL of recently-arrived threads blocked on entry. 178 JavaThread* volatile _succ; // Heir presumptive thread - used for futile wakeup throttling 179 JavaThread* volatile _Responsible; 180 181 volatile int _Spinner; // for exit->spinner handoff optimization 182 volatile int _SpinDuration; 183 184 int _contentions; // Number of active contentions in enter(). It is used by is_busy() 185 // along with other fields to determine if an ObjectMonitor can be 186 // deflated. It is also used by the async deflation protocol. See 187 // ObjectMonitor::deflate_monitor(). 188 protected: 189 ObjectWaiter* volatile _WaitSet; // LL of threads wait()ing on the monitor 190 volatile int _waiters; // number of waiting threads 191 private: 192 volatile int _WaitSetLock; // protects Wait Queue - simple spinlock 193 194 public: 195 196 static void Initialize(); 197 198 // Only perform a PerfData operation if the PerfData object has been 199 // allocated and if the PerfDataManager has not freed the PerfData 200 // objects which can happen at normal VM shutdown. 201 // 202 #define OM_PERFDATA_OP(f, op_str) \ 203 do { \ 204 if (ObjectMonitor::_sync_ ## f != nullptr && \ 205 PerfDataManager::has_PerfData()) { \ 206 ObjectMonitor::_sync_ ## f->op_str; \ 207 } \ 208 } while (0) 209 210 static PerfCounter * _sync_ContendedLockAttempts; 211 static PerfCounter * _sync_FutileWakeups; 212 static PerfCounter * _sync_Parks; 213 static PerfCounter * _sync_Notifications; 214 static PerfCounter * _sync_Inflations; 215 static PerfCounter * _sync_Deflations; 216 static PerfLongVariable * _sync_MonExtant; 217 218 static int Knob_SpinLimit; 219 220 static ByteSize header_offset() { return byte_offset_of(ObjectMonitor, _header); } 221 static ByteSize owner_offset() { return byte_offset_of(ObjectMonitor, _owner); } 222 static ByteSize recursions_offset() { return byte_offset_of(ObjectMonitor, _recursions); } 223 static ByteSize cxq_offset() { return byte_offset_of(ObjectMonitor, _cxq); } 224 static ByteSize succ_offset() { return byte_offset_of(ObjectMonitor, _succ); } 225 static ByteSize EntryList_offset() { return byte_offset_of(ObjectMonitor, _EntryList); } 226 227 // ObjectMonitor references can be ORed with markWord::monitor_value 228 // as part of the ObjectMonitor tagging mechanism. When we combine an 229 // ObjectMonitor reference with an offset, we need to remove the tag 230 // value in order to generate the proper address. 231 // 232 // We can either adjust the ObjectMonitor reference and then add the 233 // offset or we can adjust the offset that is added to the ObjectMonitor 234 // reference. The latter avoids an AGI (Address Generation Interlock) 235 // stall so the helper macro adjusts the offset value that is returned 236 // to the ObjectMonitor reference manipulation code: 237 // 238 #define OM_OFFSET_NO_MONITOR_VALUE_TAG(f) \ 239 ((in_bytes(ObjectMonitor::f ## _offset())) - markWord::monitor_value) 240 241 markWord header() const; 242 volatile markWord* header_addr(); 243 void set_header(markWord hdr); 244 245 bool is_busy() const { 246 // TODO-FIXME: assert _owner == null implies _recursions = 0 247 intptr_t ret_code = intptr_t(_waiters) | intptr_t(_cxq) | intptr_t(_EntryList); 248 int cnts = contentions(); // read once 249 if (cnts > 0) { 250 ret_code |= intptr_t(cnts); 251 } 252 if (!owner_is_DEFLATER_MARKER()) { 253 ret_code |= intptr_t(owner_raw()); 254 } 255 return ret_code != 0; 256 } 257 const char* is_busy_to_string(stringStream* ss); 258 259 bool is_entered(JavaThread* current) const; 260 261 // Returns true if this OM has an owner, false otherwise. 262 bool has_owner() const; 263 void* owner() const; // Returns null if DEFLATER_MARKER is observed. 264 void* owner_raw() const; 265 // Returns true if owner field == DEFLATER_MARKER and false otherwise. 266 bool owner_is_DEFLATER_MARKER() const; 267 // Returns true if 'this' is being async deflated and false otherwise. 268 bool is_being_async_deflated(); 269 // Clear _owner field; current value must match old_value. 270 void release_clear_owner(void* old_value); 271 // Simply set _owner field to new_value; current value must match old_value. 272 void set_owner_from(void* old_value, void* new_value); 273 // Simply set _owner field to current; current value must match basic_lock_p. 274 void set_owner_from_BasicLock(void* basic_lock_p, JavaThread* current); 275 // Try to set _owner field to new_value if the current value matches 276 // old_value, using Atomic::cmpxchg(). Otherwise, does not change the 277 // _owner field. Returns the prior value of the _owner field. 278 void* try_set_owner_from(void* old_value, void* new_value); 279 280 void set_owner_anonymous() { 281 set_owner_from(nullptr, anon_owner_ptr()); 282 } 283 284 bool is_owner_anonymous() const { 285 return owner_raw() == anon_owner_ptr(); 286 } 287 288 void set_owner_from_anonymous(Thread* owner) { 289 set_owner_from(anon_owner_ptr(), owner); 290 } 291 292 // Simply get _next_om field. 293 ObjectMonitor* next_om() const; 294 // Simply set _next_om field to new_value. 295 void set_next_om(ObjectMonitor* new_value); 296 297 int waiters() const; 298 299 int contentions() const; 300 void add_to_contentions(int value); 301 intx recursions() const { return _recursions; } 302 void set_recursions(size_t recursions); 303 304 // JVM/TI GetObjectMonitorUsage() needs this: 305 ObjectWaiter* first_waiter() { return _WaitSet; } 306 ObjectWaiter* next_waiter(ObjectWaiter* o) { return o->_next; } 307 JavaThread* thread_of_waiter(ObjectWaiter* o) { return o->_thread; } 308 309 ObjectMonitor(oop object); 310 ~ObjectMonitor(); 311 312 oop object() const; 313 oop object_peek() const; 314 315 // Returns true if the specified thread owns the ObjectMonitor. Otherwise 316 // returns false and throws IllegalMonitorStateException (IMSE). 317 bool check_owner(TRAPS); 318 319 private: 320 class ExitOnSuspend { 321 protected: 322 ObjectMonitor* _om; 323 bool _om_exited; 324 public: 325 ExitOnSuspend(ObjectMonitor* om) : _om(om), _om_exited(false) {} 326 void operator()(JavaThread* current); 327 bool exited() { return _om_exited; } 328 }; 329 class ClearSuccOnSuspend { 330 protected: 331 ObjectMonitor* _om; 332 public: 333 ClearSuccOnSuspend(ObjectMonitor* om) : _om(om) {} 334 void operator()(JavaThread* current); 335 }; 336 public: 337 bool enter_for(JavaThread* locking_thread); 338 bool enter(JavaThread* current); 339 void exit(JavaThread* current, bool not_suspended = true); 340 void wait(jlong millis, bool interruptible, TRAPS); 341 void notify(TRAPS); 342 void notifyAll(TRAPS); 343 344 void print() const; 345 #ifdef ASSERT 346 void print_debug_style_on(outputStream* st) const; 347 #endif 348 void print_on(outputStream* st) const; 349 350 // Use the following at your own risk 351 intx complete_exit(JavaThread* current); 352 353 private: 354 void AddWaiter(ObjectWaiter* waiter); 355 void INotify(JavaThread* current); 356 ObjectWaiter* DequeueWaiter(); 357 void DequeueSpecificWaiter(ObjectWaiter* waiter); 358 void EnterI(JavaThread* current); 359 void ReenterI(JavaThread* current, ObjectWaiter* current_node); 360 void UnlinkAfterAcquire(JavaThread* current, ObjectWaiter* current_node); 361 int TryLock(JavaThread* current); 362 int NotRunnable(JavaThread* current, JavaThread* Owner); 363 int TrySpin(JavaThread* current); 364 void ExitEpilog(JavaThread* current, ObjectWaiter* Wakee); 365 366 // Deflation support 367 bool deflate_monitor(); 368 void install_displaced_markword_in_object(const oop obj); 369 }; 370 371 #endif // SHARE_RUNTIME_OBJECTMONITOR_HPP --- EOF ---