1 /*
2 * Copyright (c) 1998, 2013, 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 "runtime/os.hpp"
29 #include "runtime/park.hpp"
30 #include "runtime/perfData.hpp"
31
32 // ObjectWaiter serves as a "proxy" or surrogate thread.
33 // TODO-FIXME: Eliminate ObjectWaiter and use the thread-specific
34 // ParkEvent instead. Beware, however, that the JVMTI code
35 // knows about ObjectWaiters, so we'll have to reconcile that code.
36 // See next_waiter(), first_waiter(), etc.
37
38 class ObjectWaiter : public StackObj {
39 public:
40 enum TStates { TS_UNDEF, TS_READY, TS_RUN, TS_WAIT, TS_ENTER, TS_CXQ } ;
41 enum Sorted { PREPEND, APPEND, SORTED } ;
42 ObjectWaiter * volatile _next;
43 ObjectWaiter * volatile _prev;
44 Thread* _thread;
45 jlong _notifier_tid;
46 ParkEvent * _event;
47 volatile int _notified ;
48 volatile TStates TState ;
49 Sorted _Sorted ; // List placement disposition
50 bool _active ; // Contention monitoring is enabled
51 public:
52 ObjectWaiter(Thread* thread);
53
54 void wait_reenter_begin(ObjectMonitor *mon);
55 void wait_reenter_end(ObjectMonitor *mon);
56 };
57
58 // forward declaration to avoid include tracing.hpp
59 class EventJavaMonitorWait;
60
61 // WARNING:
62 // This is a very sensitive and fragile class. DO NOT make any
63 // change unless you are fully aware of the underlying semantics.
64
65 // This class can not inherit from any other class, because I have
66 // to let the displaced header be the very first word. Otherwise I
67 // have to let markOop include this file, which would export the
68 // monitor data structure to everywhere.
69 //
70 // The ObjectMonitor class is used to implement JavaMonitors which have
71 // transformed from the lightweight structure of the thread stack to a
72 // heavy weight lock due to contention
73
74 // It is also used as RawMonitor by the JVMTI
75
76
77 class ObjectMonitor {
78 public:
79 enum {
80 OM_OK, // no error
81 OM_SYSTEM_ERROR, // operating system error
82 OM_ILLEGAL_MONITOR_STATE, // IllegalMonitorStateException
83 OM_INTERRUPTED, // Thread.interrupt()
84 OM_TIMED_OUT // Object.wait() timed out
85 };
86
87 public:
88 // TODO-FIXME: the "offset" routines should return a type of off_t instead of int ...
89 // ByteSize would also be an appropriate type.
90 static int header_offset_in_bytes() { return offset_of(ObjectMonitor, _header); }
91 static int object_offset_in_bytes() { return offset_of(ObjectMonitor, _object); }
92 static int owner_offset_in_bytes() { return offset_of(ObjectMonitor, _owner); }
93 static int count_offset_in_bytes() { return offset_of(ObjectMonitor, _count); }
94 static int recursions_offset_in_bytes() { return offset_of(ObjectMonitor, _recursions); }
95 static int cxq_offset_in_bytes() { return offset_of(ObjectMonitor, _cxq) ; }
96 static int succ_offset_in_bytes() { return offset_of(ObjectMonitor, _succ) ; }
97 static int EntryList_offset_in_bytes() { return offset_of(ObjectMonitor, _EntryList); }
98 static int FreeNext_offset_in_bytes() { return offset_of(ObjectMonitor, FreeNext); }
99 static int WaitSet_offset_in_bytes() { return offset_of(ObjectMonitor, _WaitSet) ; }
100 static int Responsible_offset_in_bytes() { return offset_of(ObjectMonitor, _Responsible);}
101 static int Spinner_offset_in_bytes() { return offset_of(ObjectMonitor, _Spinner); }
102 static int trace_exit_stack_offset_in_bytes() { return offset_of(ObjectMonitor, _trace_exit_stack); }
103
104 public:
105 // Eventaully we'll make provisions for multiple callbacks, but
106 // now one will suffice.
107 static int (*SpinCallbackFunction)(intptr_t, int) ;
108 static intptr_t SpinCallbackArgument ;
109
110
111 public:
112 markOop header() const;
113 void set_header(markOop hdr);
114
115 intptr_t is_busy() const {
116 // TODO-FIXME: merge _count and _waiters.
117 // TODO-FIXME: assert _owner == null implies _recursions = 0
118 // TODO-FIXME: assert _WaitSet != null implies _count > 0
119 return _count|_waiters|intptr_t(_owner)|intptr_t(_cxq)|intptr_t(_EntryList ) ;
120 }
121
122 intptr_t is_entered(Thread* current) const;
123
124 void* owner() const;
125 void set_owner(void* owner);
126
127 intptr_t waiters() const;
128
129 intptr_t count() const;
130 void set_count(intptr_t count);
131 intptr_t contentions() const ;
132 intptr_t recursions() const { return _recursions; }
133
134 intptr_t next_trace_seq() { return Atomic::add_ptr(1, &_trace_current_seq); }
135
136 // JVM/DI GetMonitorInfo() needs this
137 ObjectWaiter* first_waiter() { return _WaitSet; }
138 ObjectWaiter* next_waiter(ObjectWaiter* o) { return o->_next; }
139 Thread* thread_of_waiter(ObjectWaiter* o) { return o->_thread; }
140
141 // initialize the monitor, exception the semaphore, all other fields
142 // are simple integers or pointers
143 ObjectMonitor() {
144 _header = NULL;
145 _count = 0;
146 _waiters = 0,
147 _recursions = 0;
148 _object = NULL;
149 _owner = NULL;
150 _WaitSet = NULL;
151 _WaitSetLock = 0 ;
152 _Responsible = NULL ;
153 _succ = NULL ;
154 _cxq = NULL ;
155 FreeNext = NULL ;
156 _EntryList = NULL ;
157 _SpinFreq = 0 ;
158 _SpinClock = 0 ;
159 OwnerIsThread = 0 ;
160 _previous_owner_tid = 0;
161 _trace_current_seq = 0;
162 _trace_exit_stack = 0;
163 }
164
165 ~ObjectMonitor() {
166 // TODO: Add asserts ...
167 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
168 // _count == 0 _EntryList == NULL etc
169 }
170
171 private:
172 void Recycle () {
173 // TODO: add stronger asserts ...
174 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
175 // _count == 0 EntryList == NULL
176 // _recursions == 0 _WaitSet == NULL
177 // TODO: assert (is_busy()|_recursions) == 0
178 _succ = NULL ;
179 _EntryList = NULL ;
180 _cxq = NULL ;
181 _WaitSet = NULL ;
182 _recursions = 0 ;
183 _SpinFreq = 0 ;
184 _SpinClock = 0 ;
185 OwnerIsThread = 0 ;
186 // tracing: do not reset _trace_current_seq, we also use it
187 // to detect pending events before a monitor is recycled
188 }
189
190 public:
191
192 void* object() const;
193 void* object_addr();
194 void set_object(void* obj);
195
196 bool check(TRAPS); // true if the thread owns the monitor.
197 void check_slow(TRAPS);
198 void clear();
199 #ifndef PRODUCT
200 void verify();
201 void print();
202 #endif
203
204 bool try_enter (TRAPS) ;
205 void enter(TRAPS);
206 void exit(bool not_suspended, TRAPS);
207 void wait(jlong millis, bool interruptable, TRAPS);
208 void notify(TRAPS);
209 void notifyAll(TRAPS);
210
211 // Use the following at your own risk
212 void complete_exit(intptr_t *saved_recursions, intptr_t *saved_trace_exit_stack, TRAPS);
213 void reenter(intptr_t saved_recursions, intptr_t saved_trace_exit_stack, TRAPS);
214
215 private:
216 void AddWaiter (ObjectWaiter * waiter) ;
217 static void DeferredInitialize();
218
219 ObjectWaiter * DequeueWaiter () ;
220 void DequeueSpecificWaiter (ObjectWaiter * waiter) ;
221 void enter (int after_wait, TRAPS);
222 void exit(intptr_t *exit_stack_id_for_wait, bool not_suspended, TRAPS);
223 int EnterI (TRAPS) ;
224 void ReenterI (Thread * Self, ObjectWaiter * SelfNode) ;
225 void UnlinkAfterAcquire (Thread * Self, ObjectWaiter * SelfNode) ;
226 int TryLock (Thread * Self) ;
227 int NotRunnable (Thread * Self, Thread * Owner) ;
228 int TrySpin_Fixed (Thread * Self) ;
229 int TrySpin_VaryFrequency (Thread * Self) ;
230 int TrySpin_VaryDuration (Thread * Self) ;
231 void ctAsserts () ;
232 void ExitEpilog (Thread * Self, ObjectWaiter * Wakee) ;
233 bool ExitSuspendEquivalent (JavaThread * Self) ;
234 void post_monitor_wait_event(EventJavaMonitorWait * event,
235 jlong notifier_tid,
236 jlong timeout,
237 bool timedout);
238
239 private:
240 friend class ObjectSynchronizer;
241 friend class ObjectWaiter;
242 friend class VMStructs;
243
244 // WARNING: this must be the very first word of ObjectMonitor
245 // This means this class can't use any virtual member functions.
246 // TODO-FIXME: assert that offsetof(_header) is 0 or get rid of the
247 // implicit 0 offset in emitted code.
248
249 volatile markOop _header; // displaced object header word - mark
250 void* volatile _object; // backward object pointer - strong root
251
252 double SharingPad [1] ; // temp to reduce false sharing
253
254 // All the following fields must be machine word aligned
255 // The VM assumes write ordering wrt these fields, which can be
256 // read from other threads.
257
258 protected: // protected for jvmtiRawMonitor
259 void * volatile _owner; // pointer to owning thread OR BasicLock
260 volatile jlong _previous_owner_tid; // thread id of the previous owner of the monitor
261 volatile intptr_t _recursions; // recursion count, 0 for first entry
262 private:
263 int OwnerIsThread ; // _owner is (Thread *) vs SP/BasicLock
264 ObjectWaiter * volatile _cxq ; // LL of recently-arrived threads blocked on entry.
265 // The list is actually composed of WaitNodes, acting
266 // as proxies for Threads.
267 protected:
268 ObjectWaiter * volatile _EntryList ; // Threads blocked on entry or reentry.
269 private:
270 Thread * volatile _succ ; // Heir presumptive thread - used for futile wakeup throttling
271 Thread * volatile _Responsible ;
272 int _PromptDrain ; // rqst to drain cxq into EntryList ASAP
273
274 volatile int _Spinner ; // for exit->spinner handoff optimization
275 volatile int _SpinFreq ; // Spin 1-out-of-N attempts: success rate
276 volatile int _SpinClock ;
277 volatile int _SpinDuration ;
278 volatile intptr_t _SpinState ; // MCS/CLH list of spinners
279
280 // TODO-FIXME: _count, _waiters and _recursions should be of
281 // type int, or int32_t but not intptr_t. There's no reason
282 // to use 64-bit fields for these variables on a 64-bit JVM.
283
284 volatile intptr_t _count; // reference count to prevent reclaimation/deflation
285 // at stop-the-world time. See deflate_idle_monitors().
286 // _count is approximately |_WaitSet| + |_EntryList|
287
288 // TODO: this class appears to be sensitive to false sharing.
289 // there might be a better location to place this field.
290 volatile intptr_t _trace_current_seq;
291 volatile intptr_t _trace_exit_stack;
292 protected:
293 volatile intptr_t _waiters; // number of waiting threads
294 private:
295 protected:
296 ObjectWaiter * volatile _WaitSet; // LL of threads wait()ing on the monitor
297 private:
298 volatile int _WaitSetLock; // protects Wait Queue - simple spinlock
299
300 public:
301 int _QMix ; // Mixed prepend queue discipline
302 ObjectMonitor * FreeNext ; // Free list linkage
303 intptr_t StatA, StatsB ;
304
305 public:
306 static void Initialize () ;
307 static PerfCounter * _sync_ContendedLockAttempts ;
308 static PerfCounter * _sync_FutileWakeups ;
309 static PerfCounter * _sync_Parks ;
310 static PerfCounter * _sync_EmptyNotifications ;
311 static PerfCounter * _sync_Notifications ;
312 static PerfCounter * _sync_SlowEnter ;
313 static PerfCounter * _sync_SlowExit ;
314 static PerfCounter * _sync_SlowNotify ;
315 static PerfCounter * _sync_SlowNotifyAll ;
316 static PerfCounter * _sync_FailedSpins ;
317 static PerfCounter * _sync_SuccessfulSpins ;
318 static PerfCounter * _sync_PrivateA ;
319 static PerfCounter * _sync_PrivateB ;
320 static PerfCounter * _sync_MonInCirculation ;
321 static PerfCounter * _sync_MonScavenged ;
322 static PerfCounter * _sync_Inflations ;
323 static PerfCounter * _sync_Deflations ;
324 static PerfLongVariable * _sync_MonExtant ;
325
326 public:
327 static int Knob_Verbose;
328 static int Knob_SpinLimit;
329 void* operator new (size_t size) throw() {
330 return AllocateHeap(size, mtInternal);
331 }
332 void* operator new[] (size_t size) throw() {
333 return operator new (size);
334 }
335 void operator delete(void* p) {
336 FreeHeap(p, mtInternal);
337 }
338 void operator delete[] (void *p) {
339 operator delete(p);
340 }
341 };
342
343 #undef TEVENT
344 #define TEVENT(nom) {if (SyncVerbose) FEVENT(nom); }
345
346 #define FEVENT(nom) { static volatile int ctr = 0 ; int v = ++ctr ; if ((v & (v-1)) == 0) { ::printf (#nom " : %d \n", v); ::fflush(stdout); }}
347
348 #undef TEVENT
349 #define TEVENT(nom) {;}
350
351
352 #endif // SHARE_VM_RUNTIME_OBJECTMONITOR_HPP