1 /* 2 * Copyright (c) 1998, 2020, 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 "runtime/os.hpp" 32 #include "runtime/park.hpp" 33 #include "runtime/perfData.hpp" 34 35 class ObjectMonitor; 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 Thread* _thread; 49 jlong _notifier_tid; 50 ParkEvent * _event; 51 volatile int _notified; 52 volatile TStates TState; 53 bool _active; // Contention monitoring is enabled 54 public: 55 ObjectWaiter(Thread* thread); 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 { 130 friend class ObjectSynchronizer; 131 friend class ObjectWaiter; 132 friend class VMStructs; 133 JVMCI_ONLY(friend class JVMCIVMStructs;) 134 135 // The sync code expects the header field to be at offset zero (0). 136 // Enforced by the assert() in header_addr(). 137 volatile markWord _header; // displaced object header word - mark 138 void* volatile _object; // backward object pointer - strong root 139 typedef enum { 140 Free = 0, // Free must be 0 for monitor to be free after memset(..,0,..). 141 New, 142 Old 143 } AllocationState; 144 AllocationState _allocation_state; 145 // Separate _header and _owner on different cache lines since both can 146 // have busy multi-threaded access. _header, _object and _allocation_state 147 // are set at initial inflation. _object and _allocation_state don't 148 // change until deflation so _object and _allocation_state are good 149 // choices to share the cache line with _header. 150 DEFINE_PAD_MINUS_SIZE(0, OM_CACHE_LINE_SIZE, sizeof(volatile markWord) + 151 sizeof(void* volatile) + sizeof(AllocationState)); 152 // Used by async deflation as a marker in the _owner field: 153 #define DEFLATER_MARKER reinterpret_cast<void*>(-1) 154 void* volatile _owner; // pointer to owning thread OR BasicLock 155 volatile jlong _previous_owner_tid; // thread id of the previous owner of the monitor 156 // Separate _owner and _next_om on different cache lines since 157 // both can have busy multi-threaded access. _previous_owner_tid is only 158 // changed by ObjectMonitor::exit() so it is a good choice to share the 159 // cache line with _owner. 160 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(void* volatile) + 161 sizeof(volatile jlong)); 162 ObjectMonitor* _next_om; // Next ObjectMonitor* linkage 163 volatile intx _recursions; // recursion count, 0 for first entry 164 ObjectWaiter* volatile _EntryList; // Threads blocked on entry or reentry. 165 // The list is actually composed of WaitNodes, 166 // acting as proxies for Threads. 167 168 ObjectWaiter* volatile _cxq; // LL of recently-arrived threads blocked on entry. 169 Thread* volatile _succ; // Heir presumptive thread - used for futile wakeup throttling 170 Thread* volatile _Responsible; 171 172 volatile int _Spinner; // for exit->spinner handoff optimization 173 volatile int _SpinDuration; 174 175 jint _contentions; // Number of active contentions in enter(). It is used by is_busy() 176 // along with other fields to determine if an ObjectMonitor can be 177 // deflated. It is also used by the async deflation protocol. See 178 // ObjectSynchronizer::deflate_monitor() and deflate_monitor_using_JT(). 179 protected: 180 ObjectWaiter* volatile _WaitSet; // LL of threads wait()ing on the monitor 181 volatile jint _waiters; // number of waiting threads 182 private: 183 volatile int _WaitSetLock; // protects Wait Queue - simple spinlock 184 185 public: 186 static void Initialize(); 187 188 // Only perform a PerfData operation if the PerfData object has been 189 // allocated and if the PerfDataManager has not freed the PerfData 190 // objects which can happen at normal VM shutdown. 191 // 192 #define OM_PERFDATA_OP(f, op_str) \ 193 do { \ 194 if (ObjectMonitor::_sync_ ## f != NULL && \ 195 PerfDataManager::has_PerfData()) { \ 196 ObjectMonitor::_sync_ ## f->op_str; \ 197 } \ 198 } while (0) 199 200 static PerfCounter * _sync_ContendedLockAttempts; 201 static PerfCounter * _sync_FutileWakeups; 202 static PerfCounter * _sync_Parks; 203 static PerfCounter * _sync_Notifications; 204 static PerfCounter * _sync_Inflations; 205 static PerfCounter * _sync_Deflations; 206 static PerfLongVariable * _sync_MonExtant; 207 208 static int Knob_SpinLimit; 209 210 void* operator new (size_t size) throw(); 211 void* operator new[] (size_t size) throw(); 212 void operator delete(void* p); 213 void operator delete[] (void* p); 214 215 // TODO-FIXME: the "offset" routines should return a type of off_t instead of int ... 216 // ByteSize would also be an appropriate type. 217 static int header_offset_in_bytes() { return offset_of(ObjectMonitor, _header); } 218 static int object_offset_in_bytes() { return offset_of(ObjectMonitor, _object); } 219 static int owner_offset_in_bytes() { return offset_of(ObjectMonitor, _owner); } 220 static int recursions_offset_in_bytes() { return offset_of(ObjectMonitor, _recursions); } 221 static int cxq_offset_in_bytes() { return offset_of(ObjectMonitor, _cxq); } 222 static int succ_offset_in_bytes() { return offset_of(ObjectMonitor, _succ); } 223 static int EntryList_offset_in_bytes() { return offset_of(ObjectMonitor, _EntryList); } 224 225 // ObjectMonitor references can be ORed with markWord::monitor_value 226 // as part of the ObjectMonitor tagging mechanism. When we combine an 227 // ObjectMonitor reference with an offset, we need to remove the tag 228 // value in order to generate the proper address. 229 // 230 // We can either adjust the ObjectMonitor reference and then add the 231 // offset or we can adjust the offset that is added to the ObjectMonitor 232 // reference. The latter avoids an AGI (Address Generation Interlock) 233 // stall so the helper macro adjusts the offset value that is returned 234 // to the ObjectMonitor reference manipulation code: 235 // 236 #define OM_OFFSET_NO_MONITOR_VALUE_TAG(f) \ 237 ((ObjectMonitor::f ## _offset_in_bytes()) - markWord::monitor_value) 238 239 markWord header() const; 240 volatile markWord* header_addr(); 241 void set_header(markWord hdr); 242 243 intptr_t is_busy() const { 244 // TODO-FIXME: assert _owner == null implies _recursions = 0 245 intptr_t ret_code = _waiters | intptr_t(_cxq) | intptr_t(_EntryList); 246 if (!AsyncDeflateIdleMonitors) { 247 ret_code |= contentions() | intptr_t(_owner); 248 } else { 249 if (contentions() > 0) { 250 ret_code |= contentions(); 251 } 252 if (_owner != DEFLATER_MARKER) { 253 ret_code |= intptr_t(_owner); 254 } 255 } 256 return ret_code; 257 } 258 const char* is_busy_to_string(stringStream* ss); 259 260 intptr_t is_entered(Thread* current) const; 261 262 void* owner() const; // Returns NULL if DEFLATER_MARKER is observed. 263 // Returns true if owner field == DEFLATER_MARKER and false otherwise. 264 bool owner_is_DEFLATER_MARKER(); 265 // Returns true if 'this' is being async deflated and false otherwise. 266 bool is_being_async_deflated(); 267 // Clear _owner field; current value must match old_value. 268 void release_clear_owner(void* old_value); 269 // Simply set _owner field to new_value; current value must match old_value. 270 void set_owner_from(void* old_value, void* new_value); 271 // Simply set _owner field to new_value; current value must match old_value1 or old_value2. 272 void set_owner_from(void* old_value1, void* old_value2, void* new_value); 273 // Simply set _owner field to self; current value must match basic_lock_p. 274 void set_owner_from_BasicLock(void* basic_lock_p, Thread* self); 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 // Simply get _next_om field. 281 ObjectMonitor* next_om() const; 282 // Get _next_om field with acquire semantics. 283 ObjectMonitor* next_om_acquire() const; 284 // Simply set _next_om field to new_value. 285 void set_next_om(ObjectMonitor* new_value); 286 // Set _next_om field to new_value with release semantics. 287 void release_set_next_om(ObjectMonitor* new_value); 288 // Try to set _next_om field to new_value if the current value matches 289 // old_value, using Atomic::cmpxchg(). Otherwise, does not change the 290 // _next_om field. Returns the prior value of the _next_om field. 291 ObjectMonitor* try_set_next_om(ObjectMonitor* old_value, ObjectMonitor* new_value); 292 293 jint waiters() const; 294 295 jint contentions() const; 296 void add_to_contentions(jint value); 297 intx recursions() const { return _recursions; } 298 299 // JVM/TI GetObjectMonitorUsage() needs this: 300 ObjectWaiter* first_waiter() { return _WaitSet; } 301 ObjectWaiter* next_waiter(ObjectWaiter* o) { return o->_next; } 302 Thread* thread_of_waiter(ObjectWaiter* o) { return o->_thread; } 303 304 protected: 305 // We don't typically expect or want the ctors or dtors to run. 306 // normal ObjectMonitors are type-stable and immortal. 307 ObjectMonitor() { ::memset((void*)this, 0, sizeof(*this)); } 308 309 ~ObjectMonitor() { 310 // TODO: Add asserts ... 311 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0 312 // _contentions == 0 _EntryList == NULL etc 313 } 314 315 private: 316 void Recycle() { 317 // TODO: add stronger asserts ... 318 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0 319 // _contentions == 0 EntryList == NULL 320 // _recursions == 0 _WaitSet == NULL 321 #ifdef ASSERT 322 stringStream ss; 323 #endif 324 assert((is_busy() | _recursions) == 0, "freeing in-use monitor: %s, " 325 "recursions=" INTX_FORMAT, is_busy_to_string(&ss), _recursions); 326 _succ = NULL; 327 _EntryList = NULL; 328 _cxq = NULL; 329 _WaitSet = NULL; 330 _recursions = 0; 331 } 332 333 public: 334 335 void* object() const; 336 void* object_addr(); 337 void set_object(void* obj); 338 void release_set_allocation_state(AllocationState s); 339 void set_allocation_state(AllocationState s); 340 AllocationState allocation_state() const; 341 AllocationState allocation_state_acquire() const; 342 bool is_free() const; 343 bool is_old() const; 344 bool is_new() const; 345 346 // Returns true if the specified thread owns the ObjectMonitor. Otherwise 347 // returns false and throws IllegalMonitorStateException (IMSE). 348 bool check_owner(Thread* THREAD); 349 void clear(); 350 void clear_common(); 351 352 bool enter(TRAPS); 353 void exit(bool not_suspended, TRAPS); 354 void wait(jlong millis, bool interruptable, TRAPS); 355 void notify(TRAPS); 356 void notifyAll(TRAPS); 357 358 void print() const; 359 #ifdef ASSERT 360 void print_debug_style_on(outputStream* st) const; 361 #endif 362 void print_on(outputStream* st) const; 363 364 // Use the following at your own risk 365 intx complete_exit(TRAPS); 366 bool reenter(intx recursions, TRAPS); 367 368 private: 369 void AddWaiter(ObjectWaiter* waiter); 370 void INotify(Thread* self); 371 ObjectWaiter* DequeueWaiter(); 372 void DequeueSpecificWaiter(ObjectWaiter* waiter); 373 void EnterI(TRAPS); 374 void ReenterI(Thread* self, ObjectWaiter* self_node); 375 void UnlinkAfterAcquire(Thread* self, ObjectWaiter* self_node); 376 int TryLock(Thread* self); 377 int NotRunnable(Thread* self, Thread* Owner); 378 int TrySpin(Thread* self); 379 void ExitEpilog(Thread* self, ObjectWaiter* Wakee); 380 bool ExitSuspendEquivalent(JavaThread* self); 381 void install_displaced_markword_in_object(const oop obj); 382 }; 383 384 // Macro to use guarantee() for more strict AsyncDeflateIdleMonitors 385 // checks and assert() otherwise. 386 #define ADIM_guarantee(p, ...) \ 387 do { \ 388 if (AsyncDeflateIdleMonitors) { \ 389 guarantee(p, __VA_ARGS__); \ 390 } else { \ 391 assert(p, __VA_ARGS__); \ 392 } \ 393 } while (0) 394 395 #endif // SHARE_RUNTIME_OBJECTMONITOR_HPP