1 /* 2 * Copyright (c) 1998, 2019, 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 enum Sorted { PREPEND, APPEND, SORTED }; 47 ObjectWaiter* volatile _next; 48 ObjectWaiter* volatile _prev; 49 Thread* _thread; 50 jlong _notifier_tid; 51 ParkEvent * _event; 52 volatile int _notified; 53 volatile TStates TState; 54 Sorted _Sorted; // List placement disposition 55 bool _active; // Contention monitoring is enabled 56 public: 57 ObjectWaiter(Thread* thread); 58 59 void wait_reenter_begin(ObjectMonitor *mon); 60 void wait_reenter_end(ObjectMonitor *mon); 61 }; 62 63 // The ObjectMonitor class implements the heavyweight version of a 64 // JavaMonitor. The lightweight BasicLock/stack lock version has been 65 // inflated into an ObjectMonitor. This inflation is typically due to 66 // contention or use of Object.wait(). 67 // 68 // WARNING: This is a very sensitive and fragile class. DO NOT make any 69 // changes unless you are fully aware of the underlying semantics. 70 // 71 // Class JvmtiRawMonitor currently inherits from ObjectMonitor so 72 // changes in this class must be careful to not break JvmtiRawMonitor. 73 // These two subsystems should be separated. 74 // 75 // ObjectMonitor Layout Overview/Highlights/Restrictions: 76 // 77 // - The _header field must be at offset 0 because the displaced header 78 // from markWord is stored there. We do not want markWord.hpp to include 79 // ObjectMonitor.hpp to avoid exposing ObjectMonitor everywhere. This 80 // means that ObjectMonitor cannot inherit from any other class nor can 81 // it use any virtual member functions. This restriction is critical to 82 // the proper functioning of the VM. 83 // - The _header and _owner fields should be separated by enough space 84 // to avoid false sharing due to parallel access by different threads. 85 // This is an advisory recommendation. 86 // - The general layout of the fields in ObjectMonitor is: 87 // _header 88 // <lightly_used_fields> 89 // <optional padding> 90 // _owner 91 // <remaining_fields> 92 // - The VM assumes write ordering and machine word alignment with 93 // respect to the _owner field and the <remaining_fields> that can 94 // be read in parallel by other threads. 95 // - Generally fields that are accessed closely together in time should 96 // be placed proximally in space to promote data cache locality. That 97 // is, temporal locality should condition spatial locality. 98 // - We have to balance avoiding false sharing with excessive invalidation 99 // from coherence traffic. As such, we try to cluster fields that tend 100 // to be _written_ at approximately the same time onto the same data 101 // cache line. 102 // - We also have to balance the natural tension between minimizing 103 // single threaded capacity misses with excessive multi-threaded 104 // coherency misses. There is no single optimal layout for both 105 // single-threaded and multi-threaded environments. 106 // 107 // - See TEST_VM(ObjectMonitor, sanity) gtest for how critical restrictions are 108 // enforced. 109 // - Adjacent ObjectMonitors should be separated by enough space to avoid 110 // false sharing. This is handled by the ObjectMonitor allocation code 111 // in synchronizer.cpp. Also see TEST_VM(SynchronizerTest, sanity) gtest. 112 // 113 // Futures notes: 114 // - Separating _owner from the <remaining_fields> by enough space to 115 // avoid false sharing might be profitable. Given 116 // http://blogs.oracle.com/dave/entry/cas_and_cache_trivia_invalidate 117 // we know that the CAS in monitorenter will invalidate the line 118 // underlying _owner. We want to avoid an L1 data cache miss on that 119 // same line for monitorexit. Putting these <remaining_fields>: 120 // _recursions, _EntryList, _cxq, and _succ, all of which may be 121 // fetched in the inflated unlock path, on a different cache line 122 // would make them immune to CAS-based invalidation from the _owner 123 // field. 124 // 125 // - The _recursions field should be of type int, or int32_t but not 126 // intptr_t. There's no reason to use a 64-bit type for this field 127 // in a 64-bit JVM. 128 129 #ifndef OM_CACHE_LINE_SIZE 130 // Use DEFAULT_CACHE_LINE_SIZE if not already specified for 131 // the current build platform. 132 #define OM_CACHE_LINE_SIZE DEFAULT_CACHE_LINE_SIZE 133 #endif 134 135 class ObjectMonitor { 136 public: 137 enum { 138 OM_OK, // no error 139 OM_SYSTEM_ERROR, // operating system error 140 OM_ILLEGAL_MONITOR_STATE, // IllegalMonitorStateException 141 OM_INTERRUPTED, // Thread.interrupt() 142 OM_TIMED_OUT // Object.wait() timed out 143 }; 144 145 private: 146 friend class ObjectMonitorHandle; 147 friend class ObjectSynchronizer; 148 friend class ObjectWaiter; 149 friend class VMStructs; 150 JVMCI_ONLY(friend class JVMCIVMStructs;) 151 152 // The sync code expects the header field to be at offset zero (0). 153 // Enforced by the assert() in header_addr(). 154 volatile markWord _header; // displaced object header word - mark 155 void* volatile _object; // backward object pointer - strong root 156 typedef enum { 157 Free = 0, // Free must be 0 for monitor to be free after memset(..,0,..). 158 New, 159 Old 160 } AllocationState; 161 AllocationState _allocation_state; 162 public: 163 ObjectMonitor* _next_om; // Next ObjectMonitor* linkage 164 private: 165 // Separate _header and _owner on different cache lines since both can 166 // have busy multi-threaded access. _header, _object and _allocation_state 167 // are set at initial inflation. _object and _allocation_state don't 168 // change until deflation so _object and _allocation_state are good 169 // choices to share the cache line with _header. _next_om shares _header's 170 // cache line for pre-monitor list historical reasons. _next_om only 171 // changes if the next ObjectMonitor is deflated. 172 DEFINE_PAD_MINUS_SIZE(0, OM_CACHE_LINE_SIZE, sizeof(volatile markWord) + 173 sizeof(void* volatile) + sizeof(AllocationState) + 174 sizeof(ObjectMonitor*)); 175 // Used by async deflation as a marker in the _owner field: 176 #define DEFLATER_MARKER reinterpret_cast<void*>(-1) 177 protected: // protected for JvmtiRawMonitor 178 void* volatile _owner; // pointer to owning thread OR BasicLock 179 private: 180 volatile jlong _previous_owner_tid; // thread id of the previous owner of the monitor 181 // Separate _owner and _ref_count on different cache lines since both 182 // can have busy multi-threaded access. _previous_owner_tid is only 183 // changed by ObjectMonitor::exit() so it is a good choice to share the 184 // cache line with _owner. 185 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(void* volatile) + 186 sizeof(volatile jlong)); 187 volatile jint _ref_count; // ref count for ObjectMonitor* and used by the async deflation 188 // protocol. See ObjectSynchronizer::deflate_monitor_using_JT(). 189 protected: // protected for JvmtiRawMonitor 190 volatile intptr_t _recursions; // recursion count, 0 for first entry 191 ObjectWaiter* volatile _EntryList; // Threads blocked on entry or reentry. 192 // The list is actually composed of WaitNodes, 193 // acting as proxies for Threads. 194 private: 195 ObjectWaiter* volatile _cxq; // LL of recently-arrived threads blocked on entry. 196 Thread* volatile _succ; // Heir presumptive thread - used for futile wakeup throttling 197 Thread* volatile _Responsible; 198 199 volatile int _Spinner; // for exit->spinner handoff optimization 200 volatile int _SpinDuration; 201 202 volatile jint _contentions; // Number of active contentions in enter(). It is used by is_busy() 203 // along with other fields to determine if an ObjectMonitor can be 204 // deflated. See ObjectSynchronizer::deflate_monitor() and 205 // ObjectSynchronizer::deflate_monitor_using_JT(). 206 protected: 207 ObjectWaiter* volatile _WaitSet; // LL of threads wait()ing on the monitor 208 volatile jint _waiters; // number of waiting threads 209 private: 210 volatile int _WaitSetLock; // protects Wait Queue - simple spinlock 211 212 public: 213 static void Initialize(); 214 215 // Only perform a PerfData operation if the PerfData object has been 216 // allocated and if the PerfDataManager has not freed the PerfData 217 // objects which can happen at normal VM shutdown. 218 // 219 #define OM_PERFDATA_OP(f, op_str) \ 220 do { \ 221 if (ObjectMonitor::_sync_ ## f != NULL && \ 222 PerfDataManager::has_PerfData()) { \ 223 ObjectMonitor::_sync_ ## f->op_str; \ 224 } \ 225 } while (0) 226 227 static PerfCounter * _sync_ContendedLockAttempts; 228 static PerfCounter * _sync_FutileWakeups; 229 static PerfCounter * _sync_Parks; 230 static PerfCounter * _sync_Notifications; 231 static PerfCounter * _sync_Inflations; 232 static PerfCounter * _sync_Deflations; 233 static PerfLongVariable * _sync_MonExtant; 234 235 static int Knob_SpinLimit; 236 237 void* operator new (size_t size) throw(); 238 void* operator new[] (size_t size) throw(); 239 void operator delete(void* p); 240 void operator delete[] (void* p); 241 242 // TODO-FIXME: the "offset" routines should return a type of off_t instead of int ... 243 // ByteSize would also be an appropriate type. 244 static int header_offset_in_bytes() { return offset_of(ObjectMonitor, _header); } 245 static int object_offset_in_bytes() { return offset_of(ObjectMonitor, _object); } 246 static int owner_offset_in_bytes() { return offset_of(ObjectMonitor, _owner); } 247 static int recursions_offset_in_bytes() { return offset_of(ObjectMonitor, _recursions); } 248 static int cxq_offset_in_bytes() { return offset_of(ObjectMonitor, _cxq); } 249 static int succ_offset_in_bytes() { return offset_of(ObjectMonitor, _succ); } 250 static int EntryList_offset_in_bytes() { return offset_of(ObjectMonitor, _EntryList); } 251 252 // ObjectMonitor references can be ORed with markWord::monitor_value 253 // as part of the ObjectMonitor tagging mechanism. When we combine an 254 // ObjectMonitor reference with an offset, we need to remove the tag 255 // value in order to generate the proper address. 256 // 257 // We can either adjust the ObjectMonitor reference and then add the 258 // offset or we can adjust the offset that is added to the ObjectMonitor 259 // reference. The latter avoids an AGI (Address Generation Interlock) 260 // stall so the helper macro adjusts the offset value that is returned 261 // to the ObjectMonitor reference manipulation code: 262 // 263 #define OM_OFFSET_NO_MONITOR_VALUE_TAG(f) \ 264 ((ObjectMonitor::f ## _offset_in_bytes()) - markWord::monitor_value) 265 266 markWord header() const; 267 volatile markWord* header_addr(); 268 void set_header(markWord hdr); 269 270 intptr_t is_busy() const { 271 // TODO-FIXME: assert _owner == null implies _recursions = 0 272 // We do not include _ref_count in the is_busy() check because 273 // _ref_count is for indicating that the ObjectMonitor* is in 274 // use which is orthogonal to whether the ObjectMonitor itself 275 // is in use for a locking operation. 276 intptr_t ret_code = _contentions | _waiters | intptr_t(_cxq) | intptr_t(_EntryList); 277 if (!AsyncDeflateIdleMonitors) { 278 ret_code |= intptr_t(_owner); 279 } else { 280 if (_owner != DEFLATER_MARKER) { 281 ret_code |= intptr_t(_owner); 282 } 283 } 284 return ret_code; 285 } 286 const char* is_busy_to_string(stringStream* ss); 287 288 intptr_t is_entered(Thread* current) const; 289 290 void* owner() const; // Returns NULL if DEFLATER_MARKER is observed. 291 // Returns true if owner field == DEFLATER_MARKER and false otherwise. 292 bool owner_is_DEFLATER_MARKER(); 293 void set_owner(void* owner); 294 295 jint waiters() const; 296 297 jint contentions() const; 298 intptr_t recursions() const { return _recursions; } 299 300 // JVM/TI GetObjectMonitorUsage() needs this: 301 ObjectWaiter* first_waiter() { return _WaitSet; } 302 ObjectWaiter* next_waiter(ObjectWaiter* o) { return o->_next; } 303 Thread* thread_of_waiter(ObjectWaiter* o) { return o->_thread; } 304 305 protected: 306 // We don't typically expect or want the ctors or dtors to run. 307 // normal ObjectMonitors are type-stable and immortal. 308 ObjectMonitor() { ::memset((void*)this, 0, sizeof(*this)); } 309 310 ~ObjectMonitor() { 311 // TODO: Add asserts ... 312 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0 313 // _contentions == 0 _EntryList == NULL etc 314 } 315 316 private: 317 void Recycle() { 318 // TODO: add stronger asserts ... 319 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0 320 // _contentions == 0 EntryList == NULL 321 // _recursions == 0 _WaitSet == NULL 322 DEBUG_ONLY(stringStream ss;) 323 assert((is_busy() | _recursions) == 0, "freeing in-use monitor: %s, " 324 "recursions=" INTPTR_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_active() const; 341 bool is_old() const; 342 bool is_new() const; 343 void dec_ref_count(); 344 void inc_ref_count(); 345 jint ref_count() const; 346 347 // Returns true if the specified thread owns the ObjectMonitor. Otherwise 348 // returns false and throws IllegalMonitorStateException (IMSE). 349 bool check_owner(Thread* THREAD); 350 void clear(); 351 void clear_using_JT(); 352 353 void enter(TRAPS); 354 void exit(bool not_suspended, TRAPS); 355 void wait(jlong millis, bool interruptable, TRAPS); 356 void notify(TRAPS); 357 void notifyAll(TRAPS); 358 359 void print() const; 360 void print_on(outputStream* st) const; 361 362 // Use the following at your own risk 363 intptr_t complete_exit(TRAPS); 364 void reenter(intptr_t recursions, TRAPS); 365 366 private: 367 void AddWaiter(ObjectWaiter* waiter); 368 void INotify(Thread* self); 369 ObjectWaiter* DequeueWaiter(); 370 void DequeueSpecificWaiter(ObjectWaiter* waiter); 371 void EnterI(TRAPS); 372 void ReenterI(Thread* self, ObjectWaiter* self_node); 373 void UnlinkAfterAcquire(Thread* self, ObjectWaiter* self_node); 374 int TryLock(Thread* self); 375 int NotRunnable(Thread* self, Thread* Owner); 376 int TrySpin(Thread* self); 377 void ExitEpilog(Thread* self, ObjectWaiter* Wakee); 378 bool ExitSuspendEquivalent(JavaThread* self); 379 void install_displaced_markword_in_object(const oop obj); 380 }; 381 382 // A helper object for managing an ObjectMonitor*'s ref_count. There 383 // are special safety considerations when async deflation is used. 384 class ObjectMonitorHandle : public StackObj { 385 private: 386 ObjectMonitor* _om_ptr; 387 public: 388 ObjectMonitorHandle() { _om_ptr = NULL; } 389 ~ObjectMonitorHandle(); 390 391 ObjectMonitor* om_ptr() const { return _om_ptr; } 392 // Save the ObjectMonitor* associated with the specified markWord and 393 // increment the ref_count. 394 bool save_om_ptr(oop object, markWord mark); 395 396 // For internal used by ObjectSynchronizer::monitors_iterate(). 397 ObjectMonitorHandle(ObjectMonitor* _om_ptr); 398 // For internal use by ObjectSynchronizer::inflate(). 399 void set_om_ptr(ObjectMonitor* om_ptr); 400 }; 401 402 // Macro to use guarantee() for more strict AsyncDeflateIdleMonitors 403 // checks and assert() otherwise. 404 #define ADIM_guarantee(p, ...) \ 405 do { \ 406 if (AsyncDeflateIdleMonitors) { \ 407 guarantee(p, __VA_ARGS__); \ 408 } else { \ 409 assert(p, __VA_ARGS__); \ 410 } \ 411 } while (0) 412 413 #endif // SHARE_RUNTIME_OBJECTMONITOR_HPP