1 /*
2 * Copyright (c) 1998, 2007, 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
26 // ObjectWaiter serves as a "proxy" or surrogate thread.
27 // TODO-FIXME: Eliminate ObjectWaiter and use the thread-specific
28 // ParkEvent instead. Beware, however, that the JVMTI code
29 // knows about ObjectWaiters, so we'll have to reconcile that code.
30 // See next_waiter(), first_waiter(), etc.
31
32 class ObjectWaiter : public StackObj {
33 public:
34 enum TStates { TS_UNDEF, TS_READY, TS_RUN, TS_WAIT, TS_ENTER, TS_CXQ } ;
35 enum Sorted { PREPEND, APPEND, SORTED } ;
36 ObjectWaiter * volatile _next;
37 ObjectWaiter * volatile _prev;
38 Thread* _thread;
39 ParkEvent * _event;
40 volatile int _notified ;
41 volatile TStates TState ;
42 Sorted _Sorted ; // List placement disposition
43 bool _active ; // Contention monitoring is enabled
44 public:
45 ObjectWaiter(Thread* thread);
46
47 void wait_reenter_begin(ObjectMonitor *mon);
48 void wait_reenter_end(ObjectMonitor *mon);
49 };
50
51 // WARNING:
52 // This is a very sensitive and fragile class. DO NOT make any
53 // change unless you are fully aware of the underlying semantics.
54
55 // This class can not inherit from any other class, because I have
56 // to let the displaced header be the very first word. Otherwise I
57 // have to let markOop include this file, which would export the
58 // monitor data structure to everywhere.
59 //
60 // The ObjectMonitor class is used to implement JavaMonitors which have
61 // transformed from the lightweight structure of the thread stack to a
62 // heavy weight lock due to contention
63
64 // It is also used as RawMonitor by the JVMTI
65
66
67 class ObjectMonitor {
68 public:
69 enum {
70 OM_OK, // no error
71 OM_SYSTEM_ERROR, // operating system error
72 OM_ILLEGAL_MONITOR_STATE, // IllegalMonitorStateException
73 OM_INTERRUPTED, // Thread.interrupt()
74 OM_TIMED_OUT // Object.wait() timed out
75 };
76
77 public:
78 // TODO-FIXME: the "offset" routines should return a type of off_t instead of int ...
79 // ByteSize would also be an appropriate type.
80 static int header_offset_in_bytes() { return offset_of(ObjectMonitor, _header); }
81 static int object_offset_in_bytes() { return offset_of(ObjectMonitor, _object); }
82 static int owner_offset_in_bytes() { return offset_of(ObjectMonitor, _owner); }
83 static int count_offset_in_bytes() { return offset_of(ObjectMonitor, _count); }
84 static int recursions_offset_in_bytes() { return offset_of(ObjectMonitor, _recursions); }
85 static int cxq_offset_in_bytes() { return offset_of(ObjectMonitor, _cxq) ; }
86 static int succ_offset_in_bytes() { return offset_of(ObjectMonitor, _succ) ; }
87 static int EntryList_offset_in_bytes() { return offset_of(ObjectMonitor, _EntryList); }
88 static int FreeNext_offset_in_bytes() { return offset_of(ObjectMonitor, FreeNext); }
89 static int WaitSet_offset_in_bytes() { return offset_of(ObjectMonitor, _WaitSet) ; }
90 static int Responsible_offset_in_bytes() { return offset_of(ObjectMonitor, _Responsible);}
91 static int Spinner_offset_in_bytes() { return offset_of(ObjectMonitor, _Spinner); }
92
93 public:
94 // Eventaully we'll make provisions for multiple callbacks, but
95 // now one will suffice.
96 static int (*SpinCallbackFunction)(intptr_t, int) ;
97 static intptr_t SpinCallbackArgument ;
98
99
100 public:
101 markOop header() const;
102 void set_header(markOop hdr);
103
104 intptr_t is_busy() const {
105 // TODO-FIXME: merge _count and _waiters.
106 // TODO-FIXME: assert _owner == null implies _recursions = 0
107 // TODO-FIXME: assert _WaitSet != null implies _count > 0
108 return _count|_waiters|intptr_t(_owner)|intptr_t(_cxq)|intptr_t(_EntryList ) ;
109 }
110
111 intptr_t is_entered(Thread* current) const;
112
113 void* owner() const;
114 void set_owner(void* owner);
115
116 intptr_t waiters() const;
117
118 intptr_t count() const;
119 void set_count(intptr_t count);
120 intptr_t contentions() const ;
121 intptr_t recursions() const { return _recursions; }
122
123 // JVM/DI GetMonitorInfo() needs this
124 ObjectWaiter* first_waiter() { return _WaitSet; }
125 ObjectWaiter* next_waiter(ObjectWaiter* o) { return o->_next; }
126 Thread* thread_of_waiter(ObjectWaiter* o) { return o->_thread; }
127
128 // initialize the monitor, exception the semaphore, all other fields
129 // are simple integers or pointers
130 ObjectMonitor() {
131 _header = NULL;
132 _count = 0;
133 _waiters = 0,
134 _recursions = 0;
135 _object = NULL;
136 _owner = NULL;
137 _WaitSet = NULL;
138 _WaitSetLock = 0 ;
139 _Responsible = NULL ;
140 _succ = NULL ;
141 _cxq = NULL ;
142 FreeNext = NULL ;
143 _EntryList = NULL ;
144 _SpinFreq = 0 ;
145 _SpinClock = 0 ;
146 OwnerIsThread = 0 ;
147 }
148
149 ~ObjectMonitor() {
150 // TODO: Add asserts ...
151 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
152 // _count == 0 _EntryList == NULL etc
153 }
154
155 private:
156 void Recycle () {
157 // TODO: add stronger asserts ...
158 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
159 // _count == 0 EntryList == NULL
160 // _recursions == 0 _WaitSet == NULL
161 // TODO: assert (is_busy()|_recursions) == 0
162 _succ = NULL ;
163 _EntryList = NULL ;
164 _cxq = NULL ;
165 _WaitSet = NULL ;
166 _recursions = 0 ;
167 _SpinFreq = 0 ;
168 _SpinClock = 0 ;
169 OwnerIsThread = 0 ;
170 }
171
172 public:
173
174 void* object() const;
175 void* object_addr();
176 void set_object(void* obj);
177
178 bool check(TRAPS); // true if the thread owns the monitor.
179 void check_slow(TRAPS);
180 void clear();
181 #ifndef PRODUCT
182 void verify();
183 void print();
184 #endif
185
186 bool try_enter (TRAPS) ;
187 void enter(TRAPS);
188 void exit(TRAPS);
189 void wait(jlong millis, bool interruptable, TRAPS);
190 void notify(TRAPS);
191 void notifyAll(TRAPS);
192
193 // Use the following at your own risk
194 intptr_t complete_exit(TRAPS);
195 void reenter(intptr_t recursions, TRAPS);
196
197 private:
198 void AddWaiter (ObjectWaiter * waiter) ;
199 static void DeferredInitialize();
200
201 ObjectWaiter * DequeueWaiter () ;
202 void DequeueSpecificWaiter (ObjectWaiter * waiter) ;
203 void EnterI (TRAPS) ;
204 void ReenterI (Thread * Self, ObjectWaiter * SelfNode) ;
205 void UnlinkAfterAcquire (Thread * Self, ObjectWaiter * SelfNode) ;
206 int TryLock (Thread * Self) ;
207 int NotRunnable (Thread * Self, Thread * Owner) ;
208 int TrySpin_Fixed (Thread * Self) ;
209 int TrySpin_VaryFrequency (Thread * Self) ;
210 int TrySpin_VaryDuration (Thread * Self) ;
211 void ctAsserts () ;
212 void ExitEpilog (Thread * Self, ObjectWaiter * Wakee) ;
213 bool ExitSuspendEquivalent (JavaThread * Self) ;
214
215 private:
216 friend class ObjectSynchronizer;
217 friend class ObjectWaiter;
218 friend class VMStructs;
219
220 // WARNING: this must be the very first word of ObjectMonitor
221 // This means this class can't use any virtual member functions.
222 // TODO-FIXME: assert that offsetof(_header) is 0 or get rid of the
223 // implicit 0 offset in emitted code.
224
225 volatile markOop _header; // displaced object header word - mark
226 void* volatile _object; // backward object pointer - strong root
227
228 double SharingPad [1] ; // temp to reduce false sharing
229
230 // All the following fields must be machine word aligned
231 // The VM assumes write ordering wrt these fields, which can be
232 // read from other threads.
233
234 protected: // protected for jvmtiRawMonitor
235 void * volatile _owner; // pointer to owning thread OR BasicLock
236 volatile intptr_t _recursions; // recursion count, 0 for first entry
237 private:
238 int OwnerIsThread ; // _owner is (Thread *) vs SP/BasicLock
239 ObjectWaiter * volatile _cxq ; // LL of recently-arrived threads blocked on entry.
240 // The list is actually composed of WaitNodes, acting
241 // as proxies for Threads.
242 protected:
243 ObjectWaiter * volatile _EntryList ; // Threads blocked on entry or reentry.
244 private:
245 Thread * volatile _succ ; // Heir presumptive thread - used for futile wakeup throttling
246 Thread * volatile _Responsible ;
247 int _PromptDrain ; // rqst to drain cxq into EntryList ASAP
248
249 volatile int _Spinner ; // for exit->spinner handoff optimization
250 volatile int _SpinFreq ; // Spin 1-out-of-N attempts: success rate
251 volatile int _SpinClock ;
252 volatile int _SpinDuration ;
253 volatile intptr_t _SpinState ; // MCS/CLH list of spinners
254
255 // TODO-FIXME: _count, _waiters and _recursions should be of
256 // type int, or int32_t but not intptr_t. There's no reason
257 // to use 64-bit fields for these variables on a 64-bit JVM.
258
259 volatile intptr_t _count; // reference count to prevent reclaimation/deflation
260 // at stop-the-world time. See deflate_idle_monitors().
261 // _count is approximately |_WaitSet| + |_EntryList|
262 protected:
263 volatile intptr_t _waiters; // number of waiting threads
264 private:
265 protected:
266 ObjectWaiter * volatile _WaitSet; // LL of threads wait()ing on the monitor
267 private:
268 volatile int _WaitSetLock; // protects Wait Queue - simple spinlock
269
270 public:
271 int _QMix ; // Mixed prepend queue discipline
272 ObjectMonitor * FreeNext ; // Free list linkage
273 intptr_t StatA, StatsB ;
274
275 public:
276 static void Initialize () ;
277 static PerfCounter * _sync_ContendedLockAttempts ;
278 static PerfCounter * _sync_FutileWakeups ;
279 static PerfCounter * _sync_Parks ;
280 static PerfCounter * _sync_EmptyNotifications ;
281 static PerfCounter * _sync_Notifications ;
282 static PerfCounter * _sync_SlowEnter ;
283 static PerfCounter * _sync_SlowExit ;
284 static PerfCounter * _sync_SlowNotify ;
285 static PerfCounter * _sync_SlowNotifyAll ;
286 static PerfCounter * _sync_FailedSpins ;
287 static PerfCounter * _sync_SuccessfulSpins ;
288 static PerfCounter * _sync_PrivateA ;
289 static PerfCounter * _sync_PrivateB ;
290 static PerfCounter * _sync_MonInCirculation ;
291 static PerfCounter * _sync_MonScavenged ;
292 static PerfCounter * _sync_Inflations ;
293 static PerfCounter * _sync_Deflations ;
294 static PerfLongVariable * _sync_MonExtant ;
295
296 public:
297 static int Knob_Verbose;
298 static int Knob_SpinLimit;
299 };
300
301 #undef TEVENT
302 #define TEVENT(nom) {if (SyncVerbose) FEVENT(nom); }
303
304 #define FEVENT(nom) { static volatile int ctr = 0 ; int v = ++ctr ; if ((v & (v-1)) == 0) { ::printf (#nom " : %d \n", v); ::fflush(stdout); }}
305
306 #undef TEVENT
307 #define TEVENT(nom) {;}
308