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 ObjectMonitorHandle; 131 friend class ObjectSynchronizer; 132 friend class ObjectWaiter; 133 friend class VMStructs; 134 JVMCI_ONLY(friend class JVMCIVMStructs;) 135 136 // The sync code expects the header field to be at offset zero (0). 137 // Enforced by the assert() in header_addr(). 138 volatile markWord _header; // displaced object header word - mark 139 void* volatile _object; // backward object pointer - strong root 140 typedef enum { 141 Free = 0, // Free must be 0 for monitor to be free after memset(..,0,..). 142 New, 143 Old 144 } AllocationState; 145 AllocationState _allocation_state; 146 // Separate _header and _owner on different cache lines since both can 147 // have busy multi-threaded access. _header, _object and _allocation_state 148 // are set at initial inflation. _object and _allocation_state don't 149 // change until deflation so _object and _allocation_state are good 150 // choices to share the cache line with _header. 151 DEFINE_PAD_MINUS_SIZE(0, OM_CACHE_LINE_SIZE, sizeof(volatile markWord) + 152 sizeof(void* volatile) + sizeof(AllocationState)); 153 // Used by async deflation as a marker in the _owner field: 154 #define DEFLATER_MARKER reinterpret_cast<void*>(-1) 155 void* volatile _owner; // pointer to owning thread OR BasicLock 156 volatile jlong _previous_owner_tid; // thread id of the previous owner of the monitor 157 // Separate _owner and _ref_count on different cache lines since both 158 // can have busy multi-threaded access. _previous_owner_tid is only 159 // changed by ObjectMonitor::exit() so it is a good choice to share the 160 // cache line with _owner. 161 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(void* volatile) + 162 sizeof(volatile jlong)); 163 jint _ref_count; // ref count for ObjectMonitor* and used by the async deflation 164 // protocol. See ObjectSynchronizer::deflate_monitor_using_JT(). 165 // Separate _ref_count and _next_om on different cache lines since 166 // both can have busy multi-threaded access. 167 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile jint)); 168 ObjectMonitor* _next_om; // Next ObjectMonitor* linkage 169 volatile intx _recursions; // recursion count, 0 for first entry 170 ObjectWaiter* volatile _EntryList; // Threads blocked on entry or reentry. 171 // The list is actually composed of WaitNodes, 172 // acting as proxies for Threads. 173 174 ObjectWaiter* volatile _cxq; // LL of recently-arrived threads blocked on entry. 175 Thread* volatile _succ; // Heir presumptive thread - used for futile wakeup throttling 176 Thread* volatile _Responsible; 177 178 volatile int _Spinner; // for exit->spinner handoff optimization 179 volatile int _SpinDuration; 180 181 volatile jint _contentions; // Number of active contentions in enter(). It is used by is_busy() 182 // along with other fields to determine if an ObjectMonitor can be 183 // deflated. See ObjectSynchronizer::deflate_monitor() and 184 // ObjectSynchronizer::deflate_monitor_using_JT(). 185 protected: 186 ObjectWaiter* volatile _WaitSet; // LL of threads wait()ing on the monitor 187 volatile jint _waiters; // number of waiting threads 188 private: 189 volatile int _WaitSetLock; // protects Wait Queue - simple spinlock 190 191 public: 192 static void Initialize(); 193 194 // Only perform a PerfData operation if the PerfData object has been 195 // allocated and if the PerfDataManager has not freed the PerfData 196 // objects which can happen at normal VM shutdown. 197 // 198 #define OM_PERFDATA_OP(f, op_str) \ 199 do { \ 200 if (ObjectMonitor::_sync_ ## f != NULL && \ 201 PerfDataManager::has_PerfData()) { \ 202 ObjectMonitor::_sync_ ## f->op_str; \ 203 } \ 204 } while (0) 205 206 static PerfCounter * _sync_ContendedLockAttempts; 207 static PerfCounter * _sync_FutileWakeups; 208 static PerfCounter * _sync_Parks; 209 static PerfCounter * _sync_Notifications; 210 static PerfCounter * _sync_Inflations; 211 static PerfCounter * _sync_Deflations; 212 static PerfLongVariable * _sync_MonExtant; 213 214 static int Knob_SpinLimit; 215 216 void* operator new (size_t size) throw(); 217 void* operator new[] (size_t size) throw(); 218 void operator delete(void* p); 219 void operator delete[] (void* p); 220 221 // TODO-FIXME: the "offset" routines should return a type of off_t instead of int ... 222 // ByteSize would also be an appropriate type. 223 static int header_offset_in_bytes() { return offset_of(ObjectMonitor, _header); } 224 static int object_offset_in_bytes() { return offset_of(ObjectMonitor, _object); } 225 static int owner_offset_in_bytes() { return offset_of(ObjectMonitor, _owner); } 226 static int recursions_offset_in_bytes() { return offset_of(ObjectMonitor, _recursions); } 227 static int cxq_offset_in_bytes() { return offset_of(ObjectMonitor, _cxq); } 228 static int succ_offset_in_bytes() { return offset_of(ObjectMonitor, _succ); } 229 static int EntryList_offset_in_bytes() { return offset_of(ObjectMonitor, _EntryList); } 230 231 // ObjectMonitor references can be ORed with markWord::monitor_value 232 // as part of the ObjectMonitor tagging mechanism. When we combine an 233 // ObjectMonitor reference with an offset, we need to remove the tag 234 // value in order to generate the proper address. 235 // 236 // We can either adjust the ObjectMonitor reference and then add the 237 // offset or we can adjust the offset that is added to the ObjectMonitor 238 // reference. The latter avoids an AGI (Address Generation Interlock) 239 // stall so the helper macro adjusts the offset value that is returned 240 // to the ObjectMonitor reference manipulation code: 241 // 242 #define OM_OFFSET_NO_MONITOR_VALUE_TAG(f) \ 243 ((ObjectMonitor::f ## _offset_in_bytes()) - markWord::monitor_value) 244 245 markWord header() const; 246 volatile markWord* header_addr(); 247 void set_header(markWord hdr); 248 249 intptr_t is_busy() const { 250 // TODO-FIXME: assert _owner == null implies _recursions = 0 251 // We do not include _ref_count in the is_busy() check because 252 // _ref_count is for indicating that the ObjectMonitor* is in 253 // use which is orthogonal to whether the ObjectMonitor itself 254 // is in use for a locking operation. 255 intptr_t ret_code = _contentions | _waiters | intptr_t(_cxq) | intptr_t(_EntryList); 256 if (!AsyncDeflateIdleMonitors) { 257 ret_code |= intptr_t(_owner); 258 } else { 259 if (_owner != DEFLATER_MARKER) { 260 ret_code |= intptr_t(_owner); 261 } 262 } 263 return ret_code; 264 } 265 const char* is_busy_to_string(stringStream* ss); 266 267 intptr_t is_entered(Thread* current) const; 268 269 void* owner() const; // Returns NULL if DEFLATER_MARKER is observed. 270 // Returns true if owner field == DEFLATER_MARKER and false otherwise. 271 bool owner_is_DEFLATER_MARKER(); 272 // Clear _owner field; current value must match old_value. 273 void release_clear_owner(void* old_value); 274 // Simply set _owner field to new_value; current value must match old_value. 275 void set_owner_from(void* old_value, void* new_value); 276 // Simply set _owner field to new_value; current value must match old_value1 or old_value2. 277 void set_owner_from(void* old_value1, void* old_value2, void* new_value); 278 // Simply set _owner field to self; current value must match basic_lock_p. 279 void set_owner_from_BasicLock(void* basic_lock_p, Thread* self); 280 // Try to set _owner field to new_value if the current value matches 281 // old_value, using Atomic::cmpxchg(). Otherwise, does not change the 282 // _owner field. Returns the prior value of the _owner field. 283 void* try_set_owner_from(void* old_value, void* new_value); 284 285 ObjectMonitor* next_om() const; 286 // Simply set _next_om field to new_value. 287 void 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 intx recursions() const { return _recursions; } 297 298 // JVM/TI GetObjectMonitorUsage() needs this: 299 ObjectWaiter* first_waiter() { return _WaitSet; } 300 ObjectWaiter* next_waiter(ObjectWaiter* o) { return o->_next; } 301 Thread* thread_of_waiter(ObjectWaiter* o) { return o->_thread; } 302 303 protected: 304 // We don't typically expect or want the ctors or dtors to run. 305 // normal ObjectMonitors are type-stable and immortal. 306 ObjectMonitor() { ::memset((void*)this, 0, sizeof(*this)); } 307 308 ~ObjectMonitor() { 309 // TODO: Add asserts ... 310 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0 311 // _contentions == 0 _EntryList == NULL etc 312 } 313 314 private: 315 void Recycle() { 316 // TODO: add stronger asserts ... 317 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0 318 // _contentions == 0 EntryList == NULL 319 // _recursions == 0 _WaitSet == NULL 320 #ifdef ASSERT 321 stringStream ss; 322 #endif 323 assert((is_busy() | _recursions) == 0, "freeing in-use monitor: %s, " 324 "recursions=" INTX_FORMAT, is_busy_to_string(&ss), _recursions); 325 _succ = NULL; 326 _EntryList = NULL; 327 _cxq = NULL; 328 _WaitSet = NULL; 329 _recursions = 0; 330 } 331 332 public: 333 334 void* object() const; 335 void* object_addr(); 336 void set_object(void* obj); 337 void set_allocation_state(AllocationState s); 338 AllocationState allocation_state() const; 339 bool is_free() const; 340 bool is_old() const; 341 bool is_new() const; 342 void dec_ref_count(); 343 void inc_ref_count(); 344 jint ref_count() 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_using_JT(); 351 352 void 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 void 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 // A helper object for managing an ObjectMonitor*'s ref_count. There 385 // are special safety considerations when async deflation is used. 386 class ObjectMonitorHandle : public StackObj { 387 private: 388 ObjectMonitor* _om_ptr; 389 public: 390 ObjectMonitorHandle() { _om_ptr = NULL; } 391 ~ObjectMonitorHandle(); 392 393 ObjectMonitor* om_ptr() const { return _om_ptr; } 394 // Save the ObjectMonitor* associated with the specified markWord and 395 // increment the ref_count. 396 bool save_om_ptr(oop object, markWord mark); 397 // Save the specified ObjectMonitor* if safe and increment the ref_count. 398 bool save_om_ptr_if_safe(ObjectMonitor* om_ptr); 399 // Unset the _om_ptr field and decrement the ref_count. 400 void unset_om_ptr(); 401 402 // For internal use by ObjectSynchronizer::inflate(). 403 void set_om_ptr(ObjectMonitor* om_ptr); 404 }; 405 406 // Macro to use guarantee() for more strict AsyncDeflateIdleMonitors 407 // checks and assert() otherwise. 408 #define ADIM_guarantee(p, ...) \ 409 do { \ 410 if (AsyncDeflateIdleMonitors) { \ 411 guarantee(p, __VA_ARGS__); \ 412 } else { \ 413 assert(p, __VA_ARGS__); \ 414 } \ 415 } while (0) 416 417 #endif // SHARE_RUNTIME_OBJECTMONITOR_HPP