1 /* 2 * Copyright (c) 1998, 2018, 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_VM_RUNTIME_OBJECTMONITOR_HPP 26 #define SHARE_VM_RUNTIME_OBJECTMONITOR_HPP 27 28 #include "memory/allocation.hpp" 29 #include "memory/padded.hpp" 30 #include "runtime/os.hpp" 31 #include "runtime/park.hpp" 32 #include "runtime/perfData.hpp" 33 34 class ObjectMonitor; 35 36 // ObjectWaiter serves as a "proxy" or surrogate thread. 37 // TODO-FIXME: Eliminate ObjectWaiter and use the thread-specific 38 // ParkEvent instead. Beware, however, that the JVMTI code 39 // knows about ObjectWaiters, so we'll have to reconcile that code. 40 // See next_waiter(), first_waiter(), etc. 41 42 class ObjectWaiter : public StackObj { 43 public: 44 enum TStates { TS_UNDEF, TS_READY, TS_RUN, TS_WAIT, TS_ENTER, TS_CXQ }; 45 enum Sorted { PREPEND, APPEND, SORTED }; 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 Sorted _Sorted; // List placement disposition 54 bool _active; // Contention monitoring is enabled 55 public: 56 ObjectWaiter(Thread* thread); 57 58 void wait_reenter_begin(ObjectMonitor *mon); 59 void wait_reenter_end(ObjectMonitor *mon); 60 }; 61 62 // forward declaration to avoid include tracing.hpp 63 class EventJavaMonitorWait; 64 65 // The ObjectMonitor class implements the heavyweight version of a 66 // JavaMonitor. The lightweight BasicLock/stack lock version has been 67 // inflated into an ObjectMonitor. This inflation is typically due to 68 // contention or use of Object.wait(). 69 // 70 // WARNING: This is a very sensitive and fragile class. DO NOT make any 71 // changes unless you are fully aware of the underlying semantics. 72 // 73 // Class JvmtiRawMonitor currently inherits from ObjectMonitor so 74 // changes in this class must be careful to not break JvmtiRawMonitor. 75 // These two subsystems should be separated. 76 // 77 // ObjectMonitor Layout Overview/Highlights/Restrictions: 78 // 79 // - The _header field must be at offset 0 because the displaced header 80 // from markOop is stored there. We do not want markOop.hpp to include 81 // ObjectMonitor.hpp to avoid exposing ObjectMonitor everywhere. This 82 // means that ObjectMonitor cannot inherit from any other class nor can 83 // it use any virtual member functions. This restriction is critical to 84 // the proper functioning of the VM. 85 // - The _header and _owner fields should be separated by enough space 86 // to avoid false sharing due to parallel access by different threads. 87 // This is an advisory recommendation. 88 // - The general layout of the fields in ObjectMonitor is: 89 // _header 90 // <lightly_used_fields> 91 // <optional padding> 92 // _owner 93 // <remaining_fields> 94 // - The VM assumes write ordering and machine word alignment with 95 // respect to the _owner field and the <remaining_fields> that can 96 // be read in parallel by other threads. 97 // - Generally fields that are accessed closely together in time should 98 // be placed proximally in space to promote data cache locality. That 99 // is, temporal locality should condition spatial locality. 100 // - We have to balance avoiding false sharing with excessive invalidation 101 // from coherence traffic. As such, we try to cluster fields that tend 102 // to be _written_ at approximately the same time onto the same data 103 // cache line. 104 // - We also have to balance the natural tension between minimizing 105 // single threaded capacity misses with excessive multi-threaded 106 // coherency misses. There is no single optimal layout for both 107 // single-threaded and multi-threaded environments. 108 // 109 // - See ObjectMonitor::sanity_checks() for how critical restrictions are 110 // enforced and advisory recommendations are reported. 111 // - Adjacent ObjectMonitors should be separated by enough space to avoid 112 // false sharing. This is handled by the ObjectMonitor allocation code 113 // in synchronizer.cpp. Also see ObjectSynchronizer::sanity_checks(). 114 // 115 // Futures notes: 116 // - Separating _owner from the <remaining_fields> by enough space to 117 // avoid false sharing might be profitable. Given 118 // http://blogs.oracle.com/dave/entry/cas_and_cache_trivia_invalidate 119 // we know that the CAS in monitorenter will invalidate the line 120 // underlying _owner. We want to avoid an L1 data cache miss on that 121 // same line for monitorexit. Putting these <remaining_fields>: 122 // _recursions, _EntryList, _cxq, and _succ, all of which may be 123 // fetched in the inflated unlock path, on a different cache line 124 // would make them immune to CAS-based invalidation from the _owner 125 // field. 126 // 127 // - The _recursions field should be of type int, or int32_t but not 128 // intptr_t. There's no reason to use a 64-bit type for this field 129 // in a 64-bit JVM. 130 131 class ObjectMonitor { 132 public: 133 enum { 134 OM_OK, // no error 135 OM_SYSTEM_ERROR, // operating system error 136 OM_ILLEGAL_MONITOR_STATE, // IllegalMonitorStateException 137 OM_INTERRUPTED, // Thread.interrupt() 138 OM_TIMED_OUT // Object.wait() timed out 139 }; 140 141 private: 142 friend class ObjectSynchronizer; 143 friend class ObjectWaiter; 144 friend class VMStructs; 145 146 volatile markOop _header; // displaced object header word - mark 147 void* volatile _object; // backward object pointer - strong root 148 public: 149 ObjectMonitor* FreeNext; // Free list linkage 150 private: 151 DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE, 152 sizeof(volatile markOop) + sizeof(void * volatile) + 153 sizeof(ObjectMonitor *)); 154 protected: // protected for JvmtiRawMonitor 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 volatile intptr_t _recursions; // recursion count, 0 for first entry 158 ObjectWaiter * volatile _EntryList; // Threads blocked on entry or reentry. 159 // The list is actually composed of WaitNodes, 160 // acting as proxies for Threads. 161 private: 162 ObjectWaiter * volatile _cxq; // LL of recently-arrived threads blocked on entry. 163 Thread * volatile _succ; // Heir presumptive thread - used for futile wakeup throttling 164 Thread * volatile _Responsible; 165 166 volatile int _Spinner; // for exit->spinner handoff optimization 167 volatile int _SpinDuration; 168 169 volatile jint _count; // reference count to prevent reclamation/deflation 170 // at stop-the-world time. See deflate_idle_monitors(). 171 // _count is approximately |_WaitSet| + |_EntryList| 172 protected: 173 ObjectWaiter * volatile _WaitSet; // LL of threads wait()ing on the monitor 174 volatile jint _waiters; // number of waiting threads 175 private: 176 volatile int _WaitSetLock; // protects Wait Queue - simple spinlock 177 178 public: 179 static void Initialize(); 180 181 // Only perform a PerfData operation if the PerfData object has been 182 // allocated and if the PerfDataManager has not freed the PerfData 183 // objects which can happen at normal VM shutdown. 184 // 185 #define OM_PERFDATA_OP(f, op_str) \ 186 do { \ 187 if (ObjectMonitor::_sync_ ## f != NULL && \ 188 PerfDataManager::has_PerfData()) { \ 189 ObjectMonitor::_sync_ ## f->op_str; \ 190 } \ 191 } while (0) 192 193 static PerfCounter * _sync_ContendedLockAttempts; 194 static PerfCounter * _sync_FutileWakeups; 195 static PerfCounter * _sync_Parks; 196 static PerfCounter * _sync_Notifications; 197 static PerfCounter * _sync_Inflations; 198 static PerfCounter * _sync_Deflations; 199 static PerfLongVariable * _sync_MonExtant; 200 201 static int Knob_ExitRelease; 202 static int Knob_Verbose; 203 static int Knob_VerifyInUse; 204 static int Knob_VerifyMatch; 205 static int Knob_SpinLimit; 206 207 void* operator new (size_t size) throw(); 208 void* operator new[] (size_t size) throw(); 209 void operator delete(void* p); 210 void operator delete[] (void *p); 211 212 // TODO-FIXME: the "offset" routines should return a type of off_t instead of int ... 213 // ByteSize would also be an appropriate type. 214 static int header_offset_in_bytes() { return offset_of(ObjectMonitor, _header); } 215 static int object_offset_in_bytes() { return offset_of(ObjectMonitor, _object); } 216 static int owner_offset_in_bytes() { return offset_of(ObjectMonitor, _owner); } 217 static int count_offset_in_bytes() { return offset_of(ObjectMonitor, _count); } 218 static int recursions_offset_in_bytes() { return offset_of(ObjectMonitor, _recursions); } 219 static int cxq_offset_in_bytes() { return offset_of(ObjectMonitor, _cxq); } 220 static int succ_offset_in_bytes() { return offset_of(ObjectMonitor, _succ); } 221 static int EntryList_offset_in_bytes() { return offset_of(ObjectMonitor, _EntryList); } 222 223 // ObjectMonitor references can be ORed with markOopDesc::monitor_value 224 // as part of the ObjectMonitor tagging mechanism. When we combine an 225 // ObjectMonitor reference with an offset, we need to remove the tag 226 // value in order to generate the proper address. 227 // 228 // We can either adjust the ObjectMonitor reference and then add the 229 // offset or we can adjust the offset that is added to the ObjectMonitor 230 // reference. The latter avoids an AGI (Address Generation Interlock) 231 // stall so the helper macro adjusts the offset value that is returned 232 // to the ObjectMonitor reference manipulation code: 233 // 234 #define OM_OFFSET_NO_MONITOR_VALUE_TAG(f) \ 235 ((ObjectMonitor::f ## _offset_in_bytes()) - markOopDesc::monitor_value) 236 237 markOop header() const; 238 volatile markOop* header_addr(); 239 void set_header(markOop hdr); 240 241 intptr_t is_busy() const { 242 // TODO-FIXME: merge _count and _waiters. 243 // TODO-FIXME: assert _owner == null implies _recursions = 0 244 // TODO-FIXME: assert _WaitSet != null implies _count > 0 245 return _count|_waiters|intptr_t(_owner)|intptr_t(_cxq)|intptr_t(_EntryList); 246 } 247 248 intptr_t is_entered(Thread* current) const; 249 250 void* owner() const; 251 void set_owner(void* owner); 252 253 jint waiters() const; 254 255 jint count() const; 256 void set_count(jint count); 257 jint contentions() const; 258 intptr_t recursions() const { return _recursions; } 259 260 // JVM/TI GetObjectMonitorUsage() needs this: 261 ObjectWaiter* first_waiter() { return _WaitSet; } 262 ObjectWaiter* next_waiter(ObjectWaiter* o) { return o->_next; } 263 Thread* thread_of_waiter(ObjectWaiter* o) { return o->_thread; } 264 265 protected: 266 // We don't typically expect or want the ctors or dtors to run. 267 // normal ObjectMonitors are type-stable and immortal. 268 ObjectMonitor() { ::memset((void *)this, 0, sizeof(*this)); } 269 270 ~ObjectMonitor() { 271 // TODO: Add asserts ... 272 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0 273 // _count == 0 _EntryList == NULL etc 274 } 275 276 private: 277 void Recycle() { 278 // TODO: add stronger asserts ... 279 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0 280 // _count == 0 EntryList == NULL 281 // _recursions == 0 _WaitSet == NULL 282 assert(((is_busy()|_recursions) == 0), "freeing inuse monitor"); 283 _succ = NULL; 284 _EntryList = NULL; 285 _cxq = NULL; 286 _WaitSet = NULL; 287 _recursions = 0; 288 } 289 290 public: 291 292 void* object() const; 293 void* object_addr(); 294 void set_object(void* obj); 295 296 bool check(TRAPS); // true if the thread owns the monitor. 297 void check_slow(TRAPS); 298 void clear(); 299 static void sanity_checks(); // public for -XX:+ExecuteInternalVMTests 300 // in PRODUCT for -XX:SyncKnobs=Verbose=1 301 302 void enter(TRAPS); 303 void exit(bool not_suspended, TRAPS); 304 void wait(jlong millis, bool interruptable, TRAPS); 305 void notify(TRAPS); 306 void notifyAll(TRAPS); 307 308 // Use the following at your own risk 309 intptr_t complete_exit(TRAPS); 310 void reenter(intptr_t recursions, TRAPS); 311 312 private: 313 void AddWaiter(ObjectWaiter * waiter); 314 static void DeferredInitialize(); 315 void INotify(Thread * Self); 316 ObjectWaiter * DequeueWaiter(); 317 void DequeueSpecificWaiter(ObjectWaiter * waiter); 318 void EnterI(TRAPS); 319 void ReenterI(Thread * Self, ObjectWaiter * SelfNode); 320 void UnlinkAfterAcquire(Thread * Self, ObjectWaiter * SelfNode); 321 int TryLock(Thread * Self); 322 int NotRunnable(Thread * Self, Thread * Owner); 323 int TrySpin(Thread * Self); 324 void ExitEpilog(Thread * Self, ObjectWaiter * Wakee); 325 bool ExitSuspendEquivalent(JavaThread * Self); 326 void post_monitor_wait_event(EventJavaMonitorWait * event, 327 jlong notifier_tid, 328 jlong timeout, 329 bool timedout); 330 331 }; 332 333 #undef TEVENT 334 #define TEVENT(nom) { if (SyncVerbose) FEVENT(nom); } 335 336 #define FEVENT(nom) \ 337 { \ 338 static volatile int ctr = 0; \ 339 int v = ++ctr; \ 340 if ((v & (v - 1)) == 0) { \ 341 tty->print_cr("INFO: " #nom " : %d", v); \ 342 tty->flush(); \ 343 } \ 344 } 345 346 #undef TEVENT 347 #define TEVENT(nom) {;} 348 349 350 #endif // SHARE_VM_RUNTIME_OBJECTMONITOR_HPP