0
|
1
|
|
2 /*
|
|
3 * Copyright 1998-2005 Sun Microsystems, Inc. All Rights Reserved.
|
|
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
|
|
5 *
|
|
6 * This code is free software; you can redistribute it and/or modify it
|
|
7 * under the terms of the GNU General Public License version 2 only, as
|
|
8 * published by the Free Software Foundation.
|
|
9 *
|
|
10 * This code is distributed in the hope that it will be useful, but WITHOUT
|
|
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
|
|
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
|
|
13 * version 2 for more details (a copy is included in the LICENSE file that
|
|
14 * accompanied this code).
|
|
15 *
|
|
16 * You should have received a copy of the GNU General Public License version
|
|
17 * 2 along with this work; if not, write to the Free Software Foundation,
|
|
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
|
|
19 *
|
|
20 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
|
|
21 * CA 95054 USA or visit www.sun.com if you need additional information or
|
|
22 * have any questions.
|
|
23 *
|
|
24 */
|
|
25
|
|
26 # include "incls/_precompiled.incl"
|
|
27 # include "incls/_mutex.cpp.incl"
|
|
28
|
|
29 // o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o
|
|
30 //
|
|
31 // Native Monitor-Mutex locking - theory of operations
|
|
32 //
|
|
33 // * Native Monitors are completely unrelated to Java-level monitors,
|
|
34 // although the "back-end" slow-path implementations share a common lineage.
|
|
35 // See objectMonitor:: in synchronizer.cpp.
|
|
36 // Native Monitors do *not* support nesting or recursion but otherwise
|
|
37 // they're basically Hoare-flavor monitors.
|
|
38 //
|
|
39 // * A thread acquires ownership of a Monitor/Mutex by CASing the LockByte
|
|
40 // in the _LockWord from zero to non-zero. Note that the _Owner field
|
|
41 // is advisory and is used only to verify that the thread calling unlock()
|
|
42 // is indeed the last thread to have acquired the lock.
|
|
43 //
|
|
44 // * Contending threads "push" themselves onto the front of the contention
|
|
45 // queue -- called the cxq -- with CAS and then spin/park.
|
|
46 // The _LockWord contains the LockByte as well as the pointer to the head
|
|
47 // of the cxq. Colocating the LockByte with the cxq precludes certain races.
|
|
48 //
|
|
49 // * Using a separately addressable LockByte allows for CAS:MEMBAR or CAS:0
|
|
50 // idioms. We currently use MEMBAR in the uncontended unlock() path, as
|
|
51 // MEMBAR often has less latency than CAS. If warranted, we could switch to
|
|
52 // a CAS:0 mode, using timers to close the resultant race, as is done
|
|
53 // with Java Monitors in synchronizer.cpp.
|
|
54 //
|
|
55 // See the following for a discussion of the relative cost of atomics (CAS)
|
|
56 // MEMBAR, and ways to eliminate such instructions from the common-case paths:
|
|
57 // -- http://blogs.sun.com/dave/entry/biased_locking_in_hotspot
|
|
58 // -- http://blogs.sun.com/dave/resource/MustangSync.pdf
|
|
59 // -- http://blogs.sun.com/dave/resource/synchronization-public2.pdf
|
|
60 // -- synchronizer.cpp
|
|
61 //
|
|
62 // * Overall goals - desiderata
|
|
63 // 1. Minimize context switching
|
|
64 // 2. Minimize lock migration
|
|
65 // 3. Minimize CPI -- affinity and locality
|
|
66 // 4. Minimize the execution of high-latency instructions such as CAS or MEMBAR
|
|
67 // 5. Minimize outer lock hold times
|
|
68 // 6. Behave gracefully on a loaded system
|
|
69 //
|
|
70 // * Thread flow and list residency:
|
|
71 //
|
|
72 // Contention queue --> EntryList --> OnDeck --> Owner --> !Owner
|
|
73 // [..resident on monitor list..]
|
|
74 // [...........contending..................]
|
|
75 //
|
|
76 // -- The contention queue (cxq) contains recently-arrived threads (RATs).
|
|
77 // Threads on the cxq eventually drain into the EntryList.
|
|
78 // -- Invariant: a thread appears on at most one list -- cxq, EntryList
|
|
79 // or WaitSet -- at any one time.
|
|
80 // -- For a given monitor there can be at most one "OnDeck" thread at any
|
|
81 // given time but if needbe this particular invariant could be relaxed.
|
|
82 //
|
|
83 // * The WaitSet and EntryList linked lists are composed of ParkEvents.
|
|
84 // I use ParkEvent instead of threads as ParkEvents are immortal and
|
|
85 // type-stable, meaning we can safely unpark() a possibly stale
|
|
86 // list element in the unlock()-path. (That's benign).
|
|
87 //
|
|
88 // * Succession policy - providing for progress:
|
|
89 //
|
|
90 // As necessary, the unlock()ing thread identifies, unlinks, and unparks
|
|
91 // an "heir presumptive" tentative successor thread from the EntryList.
|
|
92 // This becomes the so-called "OnDeck" thread, of which there can be only
|
|
93 // one at any given time for a given monitor. The wakee will recontend
|
|
94 // for ownership of monitor.
|
|
95 //
|
|
96 // Succession is provided for by a policy of competitive handoff.
|
|
97 // The exiting thread does _not_ grant or pass ownership to the
|
|
98 // successor thread. (This is also referred to as "handoff" succession").
|
|
99 // Instead the exiting thread releases ownership and possibly wakes
|
|
100 // a successor, so the successor can (re)compete for ownership of the lock.
|
|
101 //
|
|
102 // Competitive handoff provides excellent overall throughput at the expense
|
|
103 // of short-term fairness. If fairness is a concern then one remedy might
|
|
104 // be to add an AcquireCounter field to the monitor. After a thread acquires
|
|
105 // the lock it will decrement the AcquireCounter field. When the count
|
|
106 // reaches 0 the thread would reset the AcquireCounter variable, abdicate
|
|
107 // the lock directly to some thread on the EntryList, and then move itself to the
|
|
108 // tail of the EntryList.
|
|
109 //
|
|
110 // But in practice most threads engage or otherwise participate in resource
|
|
111 // bounded producer-consumer relationships, so lock domination is not usually
|
|
112 // a practical concern. Recall too, that in general it's easier to construct
|
|
113 // a fair lock from a fast lock, but not vice-versa.
|
|
114 //
|
|
115 // * The cxq can have multiple concurrent "pushers" but only one concurrent
|
|
116 // detaching thread. This mechanism is immune from the ABA corruption.
|
|
117 // More precisely, the CAS-based "push" onto cxq is ABA-oblivious.
|
|
118 // We use OnDeck as a pseudo-lock to enforce the at-most-one detaching
|
|
119 // thread constraint.
|
|
120 //
|
|
121 // * Taken together, the cxq and the EntryList constitute or form a
|
|
122 // single logical queue of threads stalled trying to acquire the lock.
|
|
123 // We use two distinct lists to reduce heat on the list ends.
|
|
124 // Threads in lock() enqueue onto cxq while threads in unlock() will
|
|
125 // dequeue from the EntryList. (c.f. Michael Scott's "2Q" algorithm).
|
|
126 // A key desideratum is to minimize queue & monitor metadata manipulation
|
|
127 // that occurs while holding the "outer" monitor lock -- that is, we want to
|
|
128 // minimize monitor lock holds times.
|
|
129 //
|
|
130 // The EntryList is ordered by the prevailing queue discipline and
|
|
131 // can be organized in any convenient fashion, such as a doubly-linked list or
|
|
132 // a circular doubly-linked list. If we need a priority queue then something akin
|
|
133 // to Solaris' sleepq would work nicely. Viz.,
|
|
134 // -- http://agg.eng/ws/on10_nightly/source/usr/src/uts/common/os/sleepq.c.
|
|
135 // -- http://cvs.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/os/sleepq.c
|
|
136 // Queue discipline is enforced at ::unlock() time, when the unlocking thread
|
|
137 // drains the cxq into the EntryList, and orders or reorders the threads on the
|
|
138 // EntryList accordingly.
|
|
139 //
|
|
140 // Barring "lock barging", this mechanism provides fair cyclic ordering,
|
|
141 // somewhat similar to an elevator-scan.
|
|
142 //
|
|
143 // * OnDeck
|
|
144 // -- For a given monitor there can be at most one OnDeck thread at any given
|
|
145 // instant. The OnDeck thread is contending for the lock, but has been
|
|
146 // unlinked from the EntryList and cxq by some previous unlock() operations.
|
|
147 // Once a thread has been designated the OnDeck thread it will remain so
|
|
148 // until it manages to acquire the lock -- being OnDeck is a stable property.
|
|
149 // -- Threads on the EntryList or cxq are _not allowed to attempt lock acquisition.
|
|
150 // -- OnDeck also serves as an "inner lock" as follows. Threads in unlock() will, after
|
|
151 // having cleared the LockByte and dropped the outer lock, attempt to "trylock"
|
|
152 // OnDeck by CASing the field from null to non-null. If successful, that thread
|
|
153 // is then responsible for progress and succession and can use CAS to detach and
|
|
154 // drain the cxq into the EntryList. By convention, only this thread, the holder of
|
|
155 // the OnDeck inner lock, can manipulate the EntryList or detach and drain the
|
|
156 // RATs on the cxq into the EntryList. This avoids ABA corruption on the cxq as
|
|
157 // we allow multiple concurrent "push" operations but restrict detach concurrency
|
|
158 // to at most one thread. Having selected and detached a successor, the thread then
|
|
159 // changes the OnDeck to refer to that successor, and then unparks the successor.
|
|
160 // That successor will eventually acquire the lock and clear OnDeck. Beware
|
|
161 // that the OnDeck usage as a lock is asymmetric. A thread in unlock() transiently
|
|
162 // "acquires" OnDeck, performs queue manipulations, passes OnDeck to some successor,
|
|
163 // and then the successor eventually "drops" OnDeck. Note that there's never
|
|
164 // any sense of contention on the inner lock, however. Threads never contend
|
|
165 // or wait for the inner lock.
|
|
166 // -- OnDeck provides for futile wakeup throttling a described in section 3.3 of
|
|
167 // See http://www.usenix.org/events/jvm01/full_papers/dice/dice.pdf
|
|
168 // In a sense, OnDeck subsumes the ObjectMonitor _Succ and ObjectWaiter
|
|
169 // TState fields found in Java-level objectMonitors. (See synchronizer.cpp).
|
|
170 //
|
|
171 // * Waiting threads reside on the WaitSet list -- wait() puts
|
|
172 // the caller onto the WaitSet. Notify() or notifyAll() simply
|
|
173 // transfers threads from the WaitSet to either the EntryList or cxq.
|
|
174 // Subsequent unlock() operations will eventually unpark the notifyee.
|
|
175 // Unparking a notifee in notify() proper is inefficient - if we were to do so
|
|
176 // it's likely the notifyee would simply impale itself on the lock held
|
|
177 // by the notifier.
|
|
178 //
|
|
179 // * The mechanism is obstruction-free in that if the holder of the transient
|
|
180 // OnDeck lock in unlock() is preempted or otherwise stalls, other threads
|
|
181 // can still acquire and release the outer lock and continue to make progress.
|
|
182 // At worst, waking of already blocked contending threads may be delayed,
|
|
183 // but nothing worse. (We only use "trylock" operations on the inner OnDeck
|
|
184 // lock).
|
|
185 //
|
|
186 // * Note that thread-local storage must be initialized before a thread
|
|
187 // uses Native monitors or mutexes. The native monitor-mutex subsystem
|
|
188 // depends on Thread::current().
|
|
189 //
|
|
190 // * The monitor synchronization subsystem avoids the use of native
|
|
191 // synchronization primitives except for the narrow platform-specific
|
|
192 // park-unpark abstraction. See the comments in os_solaris.cpp regarding
|
|
193 // the semantics of park-unpark. Put another way, this monitor implementation
|
|
194 // depends only on atomic operations and park-unpark. The monitor subsystem
|
|
195 // manages all RUNNING->BLOCKED and BLOCKED->READY transitions while the
|
|
196 // underlying OS manages the READY<->RUN transitions.
|
|
197 //
|
|
198 // * The memory consistency model provide by lock()-unlock() is at least as
|
|
199 // strong or stronger than the Java Memory model defined by JSR-133.
|
|
200 // That is, we guarantee at least entry consistency, if not stronger.
|
|
201 // See http://g.oswego.edu/dl/jmm/cookbook.html.
|
|
202 //
|
|
203 // * Thread:: currently contains a set of purpose-specific ParkEvents:
|
|
204 // _MutexEvent, _ParkEvent, etc. A better approach might be to do away with
|
|
205 // the purpose-specific ParkEvents and instead implement a general per-thread
|
|
206 // stack of available ParkEvents which we could provision on-demand. The
|
|
207 // stack acts as a local cache to avoid excessive calls to ParkEvent::Allocate()
|
|
208 // and ::Release(). A thread would simply pop an element from the local stack before it
|
|
209 // enqueued or park()ed. When the contention was over the thread would
|
|
210 // push the no-longer-needed ParkEvent back onto its stack.
|
|
211 //
|
|
212 // * A slightly reduced form of ILock() and IUnlock() have been partially
|
|
213 // model-checked (Murphi) for safety and progress at T=1,2,3 and 4.
|
|
214 // It'd be interesting to see if TLA/TLC could be useful as well.
|
|
215 //
|
|
216 // * Mutex-Monitor is a low-level "leaf" subsystem. That is, the monitor
|
|
217 // code should never call other code in the JVM that might itself need to
|
|
218 // acquire monitors or mutexes. That's true *except* in the case of the
|
|
219 // ThreadBlockInVM state transition wrappers. The ThreadBlockInVM DTOR handles
|
|
220 // mutator reentry (ingress) by checking for a pending safepoint in which case it will
|
|
221 // call SafepointSynchronize::block(), which in turn may call Safepoint_lock->lock(), etc.
|
|
222 // In that particular case a call to lock() for a given Monitor can end up recursively
|
|
223 // calling lock() on another monitor. While distasteful, this is largely benign
|
|
224 // as the calls come from jacket that wraps lock(), and not from deep within lock() itself.
|
|
225 //
|
|
226 // It's unfortunate that native mutexes and thread state transitions were convolved.
|
|
227 // They're really separate concerns and should have remained that way. Melding
|
|
228 // them together was facile -- a bit too facile. The current implementation badly
|
|
229 // conflates the two concerns.
|
|
230 //
|
|
231 // * TODO-FIXME:
|
|
232 //
|
|
233 // -- Add DTRACE probes for contended acquire, contended acquired, contended unlock
|
|
234 // We should also add DTRACE probes in the ParkEvent subsystem for
|
|
235 // Park-entry, Park-exit, and Unpark.
|
|
236 //
|
|
237 // -- We have an excess of mutex-like constructs in the JVM, namely:
|
|
238 // 1. objectMonitors for Java-level synchronization (synchronizer.cpp)
|
|
239 // 2. low-level muxAcquire and muxRelease
|
|
240 // 3. low-level spinAcquire and spinRelease
|
|
241 // 4. native Mutex:: and Monitor::
|
|
242 // 5. jvm_raw_lock() and _unlock()
|
|
243 // 6. JVMTI raw monitors -- distinct from (5) despite having a confusingly
|
|
244 // similar name.
|
|
245 //
|
|
246 // o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o
|
|
247
|
|
248
|
|
249 // CASPTR() uses the canonical argument order that dominates in the literature.
|
|
250 // Our internal cmpxchg_ptr() uses a bastardized ordering to accommodate Sun .il templates.
|
|
251
|
|
252 #define CASPTR(a,c,s) intptr_t(Atomic::cmpxchg_ptr ((void *)(s),(void *)(a),(void *)(c)))
|
|
253 #define UNS(x) (uintptr_t(x))
|
|
254 #define TRACE(m) { static volatile int ctr = 0 ; int x = ++ctr ; if ((x & (x-1))==0) { ::printf ("%d:%s\n", x, #m); ::fflush(stdout); }}
|
|
255
|
|
256 // Simplistic low-quality Marsaglia SHIFT-XOR RNG.
|
|
257 // Bijective except for the trailing mask operation.
|
|
258 // Useful for spin loops as the compiler can't optimize it away.
|
|
259
|
|
260 static inline jint MarsagliaXORV (jint x) {
|
|
261 if (x == 0) x = 1|os::random() ;
|
|
262 x ^= x << 6;
|
|
263 x ^= ((unsigned)x) >> 21;
|
|
264 x ^= x << 7 ;
|
|
265 return x & 0x7FFFFFFF ;
|
|
266 }
|
|
267
|
|
268 static inline jint MarsagliaXOR (jint * const a) {
|
|
269 jint x = *a ;
|
|
270 if (x == 0) x = UNS(a)|1 ;
|
|
271 x ^= x << 6;
|
|
272 x ^= ((unsigned)x) >> 21;
|
|
273 x ^= x << 7 ;
|
|
274 *a = x ;
|
|
275 return x & 0x7FFFFFFF ;
|
|
276 }
|
|
277
|
|
278 static int Stall (int its) {
|
|
279 static volatile jint rv = 1 ;
|
|
280 volatile int OnFrame = 0 ;
|
|
281 jint v = rv ^ UNS(OnFrame) ;
|
|
282 while (--its >= 0) {
|
|
283 v = MarsagliaXORV (v) ;
|
|
284 }
|
|
285 // Make this impossible for the compiler to optimize away,
|
|
286 // but (mostly) avoid W coherency sharing on MP systems.
|
|
287 if (v == 0x12345) rv = v ;
|
|
288 return v ;
|
|
289 }
|
|
290
|
|
291 int Monitor::TryLock () {
|
|
292 intptr_t v = _LockWord.FullWord ;
|
|
293 for (;;) {
|
|
294 if ((v & _LBIT) != 0) return 0 ;
|
|
295 const intptr_t u = CASPTR (&_LockWord, v, v|_LBIT) ;
|
|
296 if (v == u) return 1 ;
|
|
297 v = u ;
|
|
298 }
|
|
299 }
|
|
300
|
|
301 int Monitor::TryFast () {
|
|
302 // Optimistic fast-path form ...
|
|
303 // Fast-path attempt for the common uncontended case.
|
|
304 // Avoid RTS->RTO $ coherence upgrade on typical SMP systems.
|
|
305 intptr_t v = CASPTR (&_LockWord, 0, _LBIT) ; // agro ...
|
|
306 if (v == 0) return 1 ;
|
|
307
|
|
308 for (;;) {
|
|
309 if ((v & _LBIT) != 0) return 0 ;
|
|
310 const intptr_t u = CASPTR (&_LockWord, v, v|_LBIT) ;
|
|
311 if (v == u) return 1 ;
|
|
312 v = u ;
|
|
313 }
|
|
314 }
|
|
315
|
|
316 int Monitor::ILocked () {
|
|
317 const intptr_t w = _LockWord.FullWord & 0xFF ;
|
|
318 assert (w == 0 || w == _LBIT, "invariant") ;
|
|
319 return w == _LBIT ;
|
|
320 }
|
|
321
|
|
322 // Polite TATAS spinlock with exponential backoff - bounded spin.
|
|
323 // Ideally we'd use processor cycles, time or vtime to control
|
|
324 // the loop, but we currently use iterations.
|
|
325 // All the constants within were derived empirically but work over
|
|
326 // over the spectrum of J2SE reference platforms.
|
|
327 // On Niagara-class systems the back-off is unnecessary but
|
|
328 // is relatively harmless. (At worst it'll slightly retard
|
|
329 // acquisition times). The back-off is critical for older SMP systems
|
|
330 // where constant fetching of the LockWord would otherwise impair
|
|
331 // scalability.
|
|
332 //
|
|
333 // Clamp spinning at approximately 1/2 of a context-switch round-trip.
|
|
334 // See synchronizer.cpp for details and rationale.
|
|
335
|
|
336 int Monitor::TrySpin (Thread * const Self) {
|
|
337 if (TryLock()) return 1 ;
|
|
338 if (!os::is_MP()) return 0 ;
|
|
339
|
|
340 int Probes = 0 ;
|
|
341 int Delay = 0 ;
|
|
342 int Steps = 0 ;
|
|
343 int SpinMax = NativeMonitorSpinLimit ;
|
|
344 int flgs = NativeMonitorFlags ;
|
|
345 for (;;) {
|
|
346 intptr_t v = _LockWord.FullWord;
|
|
347 if ((v & _LBIT) == 0) {
|
|
348 if (CASPTR (&_LockWord, v, v|_LBIT) == v) {
|
|
349 return 1 ;
|
|
350 }
|
|
351 continue ;
|
|
352 }
|
|
353
|
|
354 if ((flgs & 8) == 0) {
|
|
355 SpinPause () ;
|
|
356 }
|
|
357
|
|
358 // Periodically increase Delay -- variable Delay form
|
|
359 // conceptually: delay *= 1 + 1/Exponent
|
|
360 ++ Probes;
|
|
361 if (Probes > SpinMax) return 0 ;
|
|
362
|
|
363 if ((Probes & 0x7) == 0) {
|
|
364 Delay = ((Delay << 1)|1) & 0x7FF ;
|
|
365 // CONSIDER: Delay += 1 + (Delay/4); Delay &= 0x7FF ;
|
|
366 }
|
|
367
|
|
368 if (flgs & 2) continue ;
|
|
369
|
|
370 // Consider checking _owner's schedctl state, if OFFPROC abort spin.
|
|
371 // If the owner is OFFPROC then it's unlike that the lock will be dropped
|
|
372 // in a timely fashion, which suggests that spinning would not be fruitful
|
|
373 // or profitable.
|
|
374
|
|
375 // Stall for "Delay" time units - iterations in the current implementation.
|
|
376 // Avoid generating coherency traffic while stalled.
|
|
377 // Possible ways to delay:
|
|
378 // PAUSE, SLEEP, MEMBAR #sync, MEMBAR #halt,
|
|
379 // wr %g0,%asi, gethrtime, rdstick, rdtick, rdtsc, etc. ...
|
|
380 // Note that on Niagara-class systems we want to minimize STs in the
|
|
381 // spin loop. N1 and brethren write-around the L1$ over the xbar into the L2$.
|
|
382 // Furthermore, they don't have a W$ like traditional SPARC processors.
|
|
383 // We currently use a Marsaglia Shift-Xor RNG loop.
|
|
384 Steps += Delay ;
|
|
385 if (Self != NULL) {
|
|
386 jint rv = Self->rng[0] ;
|
|
387 for (int k = Delay ; --k >= 0; ) {
|
|
388 rv = MarsagliaXORV (rv) ;
|
|
389 if ((flgs & 4) == 0 && SafepointSynchronize::do_call_back()) return 0 ;
|
|
390 }
|
|
391 Self->rng[0] = rv ;
|
|
392 } else {
|
|
393 Stall (Delay) ;
|
|
394 }
|
|
395 }
|
|
396 }
|
|
397
|
|
398 static int ParkCommon (ParkEvent * ev, jlong timo) {
|
|
399 // Diagnostic support - periodically unwedge blocked threads
|
|
400 intx nmt = NativeMonitorTimeout ;
|
|
401 if (nmt > 0 && (nmt < timo || timo <= 0)) {
|
|
402 timo = nmt ;
|
|
403 }
|
|
404 int err = OS_OK ;
|
|
405 if (0 == timo) {
|
|
406 ev->park() ;
|
|
407 } else {
|
|
408 err = ev->park(timo) ;
|
|
409 }
|
|
410 return err ;
|
|
411 }
|
|
412
|
|
413 inline int Monitor::AcquireOrPush (ParkEvent * ESelf) {
|
|
414 intptr_t v = _LockWord.FullWord ;
|
|
415 for (;;) {
|
|
416 if ((v & _LBIT) == 0) {
|
|
417 const intptr_t u = CASPTR (&_LockWord, v, v|_LBIT) ;
|
|
418 if (u == v) return 1 ; // indicate acquired
|
|
419 v = u ;
|
|
420 } else {
|
|
421 // Anticipate success ...
|
|
422 ESelf->ListNext = (ParkEvent *) (v & ~_LBIT) ;
|
|
423 const intptr_t u = CASPTR (&_LockWord, v, intptr_t(ESelf)|_LBIT) ;
|
|
424 if (u == v) return 0 ; // indicate pushed onto cxq
|
|
425 v = u ;
|
|
426 }
|
|
427 // Interference - LockWord change - just retry
|
|
428 }
|
|
429 }
|
|
430
|
|
431 // ILock and IWait are the lowest level primitive internal blocking
|
|
432 // synchronization functions. The callers of IWait and ILock must have
|
|
433 // performed any needed state transitions beforehand.
|
|
434 // IWait and ILock may directly call park() without any concern for thread state.
|
|
435 // Note that ILock and IWait do *not* access _owner.
|
|
436 // _owner is a higher-level logical concept.
|
|
437
|
|
438 void Monitor::ILock (Thread * Self) {
|
|
439 assert (_OnDeck != Self->_MutexEvent, "invariant") ;
|
|
440
|
|
441 if (TryFast()) {
|
|
442 Exeunt:
|
|
443 assert (ILocked(), "invariant") ;
|
|
444 return ;
|
|
445 }
|
|
446
|
|
447 ParkEvent * const ESelf = Self->_MutexEvent ;
|
|
448 assert (_OnDeck != ESelf, "invariant") ;
|
|
449
|
|
450 // As an optimization, spinners could conditionally try to set ONDECK to _LBIT
|
|
451 // Synchronizer.cpp uses a similar optimization.
|
|
452 if (TrySpin (Self)) goto Exeunt ;
|
|
453
|
|
454 // Slow-path - the lock is contended.
|
|
455 // Either Enqueue Self on cxq or acquire the outer lock.
|
|
456 // LockWord encoding = (cxq,LOCKBYTE)
|
|
457 ESelf->reset() ;
|
|
458 OrderAccess::fence() ;
|
|
459
|
|
460 // Optional optimization ... try barging on the inner lock
|
|
461 if ((NativeMonitorFlags & 32) && CASPTR (&_OnDeck, NULL, UNS(Self)) == 0) {
|
|
462 goto OnDeck_LOOP ;
|
|
463 }
|
|
464
|
|
465 if (AcquireOrPush (ESelf)) goto Exeunt ;
|
|
466
|
|
467 // At any given time there is at most one ondeck thread.
|
|
468 // ondeck implies not resident on cxq and not resident on EntryList
|
|
469 // Only the OnDeck thread can try to acquire -- contended for -- the lock.
|
|
470 // CONSIDER: use Self->OnDeck instead of m->OnDeck.
|
|
471 // Deschedule Self so that others may run.
|
|
472 while (_OnDeck != ESelf) {
|
|
473 ParkCommon (ESelf, 0) ;
|
|
474 }
|
|
475
|
|
476 // Self is now in the ONDECK position and will remain so until it
|
|
477 // manages to acquire the lock.
|
|
478 OnDeck_LOOP:
|
|
479 for (;;) {
|
|
480 assert (_OnDeck == ESelf, "invariant") ;
|
|
481 if (TrySpin (Self)) break ;
|
|
482 // CONSIDER: if ESelf->TryPark() && TryLock() break ...
|
|
483 // It's probably wise to spin only if we *actually* blocked
|
|
484 // CONSIDER: check the lockbyte, if it remains set then
|
|
485 // preemptively drain the cxq into the EntryList.
|
|
486 // The best place and time to perform queue operations -- lock metadata --
|
|
487 // is _before having acquired the outer lock, while waiting for the lock to drop.
|
|
488 ParkCommon (ESelf, 0) ;
|
|
489 }
|
|
490
|
|
491 assert (_OnDeck == ESelf, "invariant") ;
|
|
492 _OnDeck = NULL ;
|
|
493
|
|
494 // Note that we current drop the inner lock (clear OnDeck) in the slow-path
|
|
495 // epilog immediately after having acquired the outer lock.
|
|
496 // But instead we could consider the following optimizations:
|
|
497 // A. Shift or defer dropping the inner lock until the subsequent IUnlock() operation.
|
|
498 // This might avoid potential reacquisition of the inner lock in IUlock().
|
|
499 // B. While still holding the inner lock, attempt to opportunistically select
|
|
500 // and unlink the next ONDECK thread from the EntryList.
|
|
501 // If successful, set ONDECK to refer to that thread, otherwise clear ONDECK.
|
|
502 // It's critical that the select-and-unlink operation run in constant-time as
|
|
503 // it executes when holding the outer lock and may artificially increase the
|
|
504 // effective length of the critical section.
|
|
505 // Note that (A) and (B) are tantamount to succession by direct handoff for
|
|
506 // the inner lock.
|
|
507 goto Exeunt ;
|
|
508 }
|
|
509
|
|
510 void Monitor::IUnlock (bool RelaxAssert) {
|
|
511 assert (ILocked(), "invariant") ;
|
|
512 _LockWord.Bytes[_LSBINDEX] = 0 ; // drop outer lock
|
|
513 OrderAccess::storeload ();
|
|
514 ParkEvent * const w = _OnDeck ;
|
|
515 assert (RelaxAssert || w != Thread::current()->_MutexEvent, "invariant") ;
|
|
516 if (w != NULL) {
|
|
517 // Either we have a valid ondeck thread or ondeck is transiently "locked"
|
|
518 // by some exiting thread as it arranges for succession. The LSBit of
|
|
519 // OnDeck allows us to discriminate two cases. If the latter, the
|
|
520 // responsibility for progress and succession lies with that other thread.
|
|
521 // For good performance, we also depend on the fact that redundant unpark()
|
|
522 // operations are cheap. That is, repeated Unpark()ing of the ONDECK thread
|
|
523 // is inexpensive. This approach provides implicit futile wakeup throttling.
|
|
524 // Note that the referent "w" might be stale with respect to the lock.
|
|
525 // In that case the following unpark() is harmless and the worst that'll happen
|
|
526 // is a spurious return from a park() operation. Critically, if "w" _is stale,
|
|
527 // then progress is known to have occurred as that means the thread associated
|
|
528 // with "w" acquired the lock. In that case this thread need take no further
|
|
529 // action to guarantee progress.
|
|
530 if ((UNS(w) & _LBIT) == 0) w->unpark() ;
|
|
531 return ;
|
|
532 }
|
|
533
|
|
534 intptr_t cxq = _LockWord.FullWord ;
|
|
535 if (((cxq & ~_LBIT)|UNS(_EntryList)) == 0) {
|
|
536 return ; // normal fast-path exit - cxq and EntryList both empty
|
|
537 }
|
|
538 if (cxq & _LBIT) {
|
|
539 // Optional optimization ...
|
|
540 // Some other thread acquired the lock in the window since this
|
|
541 // thread released it. Succession is now that thread's responsibility.
|
|
542 return ;
|
|
543 }
|
|
544
|
|
545 Succession:
|
|
546 // Slow-path exit - this thread must ensure succession and progress.
|
|
547 // OnDeck serves as lock to protect cxq and EntryList.
|
|
548 // Only the holder of OnDeck can manipulate EntryList or detach the RATs from cxq.
|
|
549 // Avoid ABA - allow multiple concurrent producers (enqueue via push-CAS)
|
|
550 // but only one concurrent consumer (detacher of RATs).
|
|
551 // Consider protecting this critical section with schedctl on Solaris.
|
|
552 // Unlike a normal lock, however, the exiting thread "locks" OnDeck,
|
|
553 // picks a successor and marks that thread as OnDeck. That successor
|
|
554 // thread will then clear OnDeck once it eventually acquires the outer lock.
|
|
555 if (CASPTR (&_OnDeck, NULL, _LBIT) != UNS(NULL)) {
|
|
556 return ;
|
|
557 }
|
|
558
|
|
559 ParkEvent * List = _EntryList ;
|
|
560 if (List != NULL) {
|
|
561 // Transfer the head of the EntryList to the OnDeck position.
|
|
562 // Once OnDeck, a thread stays OnDeck until it acquires the lock.
|
|
563 // For a given lock there is at most OnDeck thread at any one instant.
|
|
564 WakeOne:
|
|
565 assert (List == _EntryList, "invariant") ;
|
|
566 ParkEvent * const w = List ;
|
|
567 assert (RelaxAssert || w != Thread::current()->_MutexEvent, "invariant") ;
|
|
568 _EntryList = w->ListNext ;
|
|
569 // as a diagnostic measure consider setting w->_ListNext = BAD
|
|
570 assert (UNS(_OnDeck) == _LBIT, "invariant") ;
|
|
571 _OnDeck = w ; // pass OnDeck to w.
|
|
572 // w will clear OnDeck once it acquires the outer lock
|
|
573
|
|
574 // Another optional optimization ...
|
|
575 // For heavily contended locks it's not uncommon that some other
|
|
576 // thread acquired the lock while this thread was arranging succession.
|
|
577 // Try to defer the unpark() operation - Delegate the responsibility
|
|
578 // for unpark()ing the OnDeck thread to the current or subsequent owners
|
|
579 // That is, the new owner is responsible for unparking the OnDeck thread.
|
|
580 OrderAccess::storeload() ;
|
|
581 cxq = _LockWord.FullWord ;
|
|
582 if (cxq & _LBIT) return ;
|
|
583
|
|
584 w->unpark() ;
|
|
585 return ;
|
|
586 }
|
|
587
|
|
588 cxq = _LockWord.FullWord ;
|
|
589 if ((cxq & ~_LBIT) != 0) {
|
|
590 // The EntryList is empty but the cxq is populated.
|
|
591 // drain RATs from cxq into EntryList
|
|
592 // Detach RATs segment with CAS and then merge into EntryList
|
|
593 for (;;) {
|
|
594 // optional optimization - if locked, the owner is responsible for succession
|
|
595 if (cxq & _LBIT) goto Punt ;
|
|
596 const intptr_t vfy = CASPTR (&_LockWord, cxq, cxq & _LBIT) ;
|
|
597 if (vfy == cxq) break ;
|
|
598 cxq = vfy ;
|
|
599 // Interference - LockWord changed - Just retry
|
|
600 // We can see concurrent interference from contending threads
|
|
601 // pushing themselves onto the cxq or from lock-unlock operations.
|
|
602 // From the perspective of this thread, EntryList is stable and
|
|
603 // the cxq is prepend-only -- the head is volatile but the interior
|
|
604 // of the cxq is stable. In theory if we encounter interference from threads
|
|
605 // pushing onto cxq we could simply break off the original cxq suffix and
|
|
606 // move that segment to the EntryList, avoiding a 2nd or multiple CAS attempts
|
|
607 // on the high-traffic LockWord variable. For instance lets say the cxq is "ABCD"
|
|
608 // when we first fetch cxq above. Between the fetch -- where we observed "A"
|
|
609 // -- and CAS -- where we attempt to CAS null over A -- "PQR" arrive,
|
|
610 // yielding cxq = "PQRABCD". In this case we could simply set A.ListNext
|
|
611 // null, leaving cxq = "PQRA" and transfer the "BCD" segment to the EntryList.
|
|
612 // Note too, that it's safe for this thread to traverse the cxq
|
|
613 // without taking any special concurrency precautions.
|
|
614 }
|
|
615
|
|
616 // We don't currently reorder the cxq segment as we move it onto
|
|
617 // the EntryList, but it might make sense to reverse the order
|
|
618 // or perhaps sort by thread priority. See the comments in
|
|
619 // synchronizer.cpp objectMonitor::exit().
|
|
620 assert (_EntryList == NULL, "invariant") ;
|
|
621 _EntryList = List = (ParkEvent *)(cxq & ~_LBIT) ;
|
|
622 assert (List != NULL, "invariant") ;
|
|
623 goto WakeOne ;
|
|
624 }
|
|
625
|
|
626 // cxq|EntryList is empty.
|
|
627 // w == NULL implies that cxq|EntryList == NULL in the past.
|
|
628 // Possible race - rare inopportune interleaving.
|
|
629 // A thread could have added itself to cxq since this thread previously checked.
|
|
630 // Detect and recover by refetching cxq.
|
|
631 Punt:
|
|
632 assert (UNS(_OnDeck) == _LBIT, "invariant") ;
|
|
633 _OnDeck = NULL ; // Release inner lock.
|
|
634 OrderAccess::storeload(); // Dekker duality - pivot point
|
|
635
|
|
636 // Resample LockWord/cxq to recover from possible race.
|
|
637 // For instance, while this thread T1 held OnDeck, some other thread T2 might
|
|
638 // acquire the outer lock. Another thread T3 might try to acquire the outer
|
|
639 // lock, but encounter contention and enqueue itself on cxq. T2 then drops the
|
|
640 // outer lock, but skips succession as this thread T1 still holds OnDeck.
|
|
641 // T1 is and remains responsible for ensuring succession of T3.
|
|
642 //
|
|
643 // Note that we don't need to recheck EntryList, just cxq.
|
|
644 // If threads moved onto EntryList since we dropped OnDeck
|
|
645 // that implies some other thread forced succession.
|
|
646 cxq = _LockWord.FullWord ;
|
|
647 if ((cxq & ~_LBIT) != 0 && (cxq & _LBIT) == 0) {
|
|
648 goto Succession ; // potential race -- re-run succession
|
|
649 }
|
|
650 return ;
|
|
651 }
|
|
652
|
|
653 bool Monitor::notify() {
|
|
654 assert (_owner == Thread::current(), "invariant") ;
|
|
655 assert (ILocked(), "invariant") ;
|
|
656 if (_WaitSet == NULL) return true ;
|
|
657 NotifyCount ++ ;
|
|
658
|
|
659 // Transfer one thread from the WaitSet to the EntryList or cxq.
|
|
660 // Currently we just unlink the head of the WaitSet and prepend to the cxq.
|
|
661 // And of course we could just unlink it and unpark it, too, but
|
|
662 // in that case it'd likely impale itself on the reentry.
|
|
663 Thread::muxAcquire (_WaitLock, "notify:WaitLock") ;
|
|
664 ParkEvent * nfy = _WaitSet ;
|
|
665 if (nfy != NULL) { // DCL idiom
|
|
666 _WaitSet = nfy->ListNext ;
|
|
667 assert (nfy->Notified == 0, "invariant") ;
|
|
668 // push nfy onto the cxq
|
|
669 for (;;) {
|
|
670 const intptr_t v = _LockWord.FullWord ;
|
|
671 assert ((v & 0xFF) == _LBIT, "invariant") ;
|
|
672 nfy->ListNext = (ParkEvent *)(v & ~_LBIT);
|
|
673 if (CASPTR (&_LockWord, v, UNS(nfy)|_LBIT) == v) break;
|
|
674 // interference - _LockWord changed -- just retry
|
|
675 }
|
|
676 // Note that setting Notified before pushing nfy onto the cxq is
|
|
677 // also legal and safe, but the safety properties are much more
|
|
678 // subtle, so for the sake of code stewardship ...
|
|
679 OrderAccess::fence() ;
|
|
680 nfy->Notified = 1;
|
|
681 }
|
|
682 Thread::muxRelease (_WaitLock) ;
|
|
683 if (nfy != NULL && (NativeMonitorFlags & 16)) {
|
|
684 // Experimental code ... light up the wakee in the hope that this thread (the owner)
|
|
685 // will drop the lock just about the time the wakee comes ONPROC.
|
|
686 nfy->unpark() ;
|
|
687 }
|
|
688 assert (ILocked(), "invariant") ;
|
|
689 return true ;
|
|
690 }
|
|
691
|
|
692 // Currently notifyAll() transfers the waiters one-at-a-time from the waitset
|
|
693 // to the cxq. This could be done more efficiently with a single bulk en-mass transfer,
|
|
694 // but in practice notifyAll() for large #s of threads is rare and not time-critical.
|
|
695 // Beware too, that we invert the order of the waiters. Lets say that the
|
|
696 // waitset is "ABCD" and the cxq is "XYZ". After a notifyAll() the waitset
|
|
697 // will be empty and the cxq will be "DCBAXYZ". This is benign, of course.
|
|
698
|
|
699 bool Monitor::notify_all() {
|
|
700 assert (_owner == Thread::current(), "invariant") ;
|
|
701 assert (ILocked(), "invariant") ;
|
|
702 while (_WaitSet != NULL) notify() ;
|
|
703 return true ;
|
|
704 }
|
|
705
|
|
706 int Monitor::IWait (Thread * Self, jlong timo) {
|
|
707 assert (ILocked(), "invariant") ;
|
|
708
|
|
709 // Phases:
|
|
710 // 1. Enqueue Self on WaitSet - currently prepend
|
|
711 // 2. unlock - drop the outer lock
|
|
712 // 3. wait for either notification or timeout
|
|
713 // 4. lock - reentry - reacquire the outer lock
|
|
714
|
|
715 ParkEvent * const ESelf = Self->_MutexEvent ;
|
|
716 ESelf->Notified = 0 ;
|
|
717 ESelf->reset() ;
|
|
718 OrderAccess::fence() ;
|
|
719
|
|
720 // Add Self to WaitSet
|
|
721 // Ideally only the holder of the outer lock would manipulate the WaitSet -
|
|
722 // That is, the outer lock would implicitly protect the WaitSet.
|
|
723 // But if a thread in wait() encounters a timeout it will need to dequeue itself
|
|
724 // from the WaitSet _before it becomes the owner of the lock. We need to dequeue
|
|
725 // as the ParkEvent -- which serves as a proxy for the thread -- can't reside
|
|
726 // on both the WaitSet and the EntryList|cxq at the same time.. That is, a thread
|
|
727 // on the WaitSet can't be allowed to compete for the lock until it has managed to
|
|
728 // unlink its ParkEvent from WaitSet. Thus the need for WaitLock.
|
|
729 // Contention on the WaitLock is minimal.
|
|
730 //
|
|
731 // Another viable approach would be add another ParkEvent, "WaitEvent" to the
|
|
732 // thread class. The WaitSet would be composed of WaitEvents. Only the
|
|
733 // owner of the outer lock would manipulate the WaitSet. A thread in wait()
|
|
734 // could then compete for the outer lock, and then, if necessary, unlink itself
|
|
735 // from the WaitSet only after having acquired the outer lock. More precisely,
|
|
736 // there would be no WaitLock. A thread in in wait() would enqueue its WaitEvent
|
|
737 // on the WaitSet; release the outer lock; wait for either notification or timeout;
|
|
738 // reacquire the inner lock; and then, if needed, unlink itself from the WaitSet.
|
|
739 //
|
|
740 // Alternatively, a 2nd set of list link fields in the ParkEvent might suffice.
|
|
741 // One set would be for the WaitSet and one for the EntryList.
|
|
742 // We could also deconstruct the ParkEvent into a "pure" event and add a
|
|
743 // new immortal/TSM "ListElement" class that referred to ParkEvents.
|
|
744 // In that case we could have one ListElement on the WaitSet and another
|
|
745 // on the EntryList, with both referring to the same pure Event.
|
|
746
|
|
747 Thread::muxAcquire (_WaitLock, "wait:WaitLock:Add") ;
|
|
748 ESelf->ListNext = _WaitSet ;
|
|
749 _WaitSet = ESelf ;
|
|
750 Thread::muxRelease (_WaitLock) ;
|
|
751
|
|
752 // Release the outer lock
|
|
753 // We call IUnlock (RelaxAssert=true) as a thread T1 might
|
|
754 // enqueue itself on the WaitSet, call IUnlock(), drop the lock,
|
|
755 // and then stall before it can attempt to wake a successor.
|
|
756 // Some other thread T2 acquires the lock, and calls notify(), moving
|
|
757 // T1 from the WaitSet to the cxq. T2 then drops the lock. T1 resumes,
|
|
758 // and then finds *itself* on the cxq. During the course of a normal
|
|
759 // IUnlock() call a thread should _never find itself on the EntryList
|
|
760 // or cxq, but in the case of wait() it's possible.
|
|
761 // See synchronizer.cpp objectMonitor::wait().
|
|
762 IUnlock (true) ;
|
|
763
|
|
764 // Wait for either notification or timeout
|
|
765 // Beware that in some circumstances we might propagate
|
|
766 // spurious wakeups back to the caller.
|
|
767
|
|
768 for (;;) {
|
|
769 if (ESelf->Notified) break ;
|
|
770 int err = ParkCommon (ESelf, timo) ;
|
|
771 if (err == OS_TIMEOUT || (NativeMonitorFlags & 1)) break ;
|
|
772 }
|
|
773
|
|
774 // Prepare for reentry - if necessary, remove ESelf from WaitSet
|
|
775 // ESelf can be:
|
|
776 // 1. Still on the WaitSet. This can happen if we exited the loop by timeout.
|
|
777 // 2. On the cxq or EntryList
|
|
778 // 3. Not resident on cxq, EntryList or WaitSet, but in the OnDeck position.
|
|
779
|
|
780 OrderAccess::fence() ;
|
|
781 int WasOnWaitSet = 0 ;
|
|
782 if (ESelf->Notified == 0) {
|
|
783 Thread::muxAcquire (_WaitLock, "wait:WaitLock:remove") ;
|
|
784 if (ESelf->Notified == 0) { // DCL idiom
|
|
785 assert (_OnDeck != ESelf, "invariant") ; // can't be both OnDeck and on WaitSet
|
|
786 // ESelf is resident on the WaitSet -- unlink it.
|
|
787 // A doubly-linked list would be better here so we can unlink in constant-time.
|
|
788 // We have to unlink before we potentially recontend as ESelf might otherwise
|
|
789 // end up on the cxq|EntryList -- it can't be on two lists at once.
|
|
790 ParkEvent * p = _WaitSet ;
|
|
791 ParkEvent * q = NULL ; // classic q chases p
|
|
792 while (p != NULL && p != ESelf) {
|
|
793 q = p ;
|
|
794 p = p->ListNext ;
|
|
795 }
|
|
796 assert (p == ESelf, "invariant") ;
|
|
797 if (p == _WaitSet) { // found at head
|
|
798 assert (q == NULL, "invariant") ;
|
|
799 _WaitSet = p->ListNext ;
|
|
800 } else { // found in interior
|
|
801 assert (q->ListNext == p, "invariant") ;
|
|
802 q->ListNext = p->ListNext ;
|
|
803 }
|
|
804 WasOnWaitSet = 1 ; // We were *not* notified but instead encountered timeout
|
|
805 }
|
|
806 Thread::muxRelease (_WaitLock) ;
|
|
807 }
|
|
808
|
|
809 // Reentry phase - reacquire the lock
|
|
810 if (WasOnWaitSet) {
|
|
811 // ESelf was previously on the WaitSet but we just unlinked it above
|
|
812 // because of a timeout. ESelf is not resident on any list and is not OnDeck
|
|
813 assert (_OnDeck != ESelf, "invariant") ;
|
|
814 ILock (Self) ;
|
|
815 } else {
|
|
816 // A prior notify() operation moved ESelf from the WaitSet to the cxq.
|
|
817 // ESelf is now on the cxq, EntryList or at the OnDeck position.
|
|
818 // The following fragment is extracted from Monitor::ILock()
|
|
819 for (;;) {
|
|
820 if (_OnDeck == ESelf && TrySpin(Self)) break ;
|
|
821 ParkCommon (ESelf, 0) ;
|
|
822 }
|
|
823 assert (_OnDeck == ESelf, "invariant") ;
|
|
824 _OnDeck = NULL ;
|
|
825 }
|
|
826
|
|
827 assert (ILocked(), "invariant") ;
|
|
828 return WasOnWaitSet != 0 ; // return true IFF timeout
|
|
829 }
|
|
830
|
|
831
|
|
832 // ON THE VMTHREAD SNEAKING PAST HELD LOCKS:
|
|
833 // In particular, there are certain types of global lock that may be held
|
|
834 // by a Java thread while it is blocked at a safepoint but before it has
|
|
835 // written the _owner field. These locks may be sneakily acquired by the
|
|
836 // VM thread during a safepoint to avoid deadlocks. Alternatively, one should
|
|
837 // identify all such locks, and ensure that Java threads never block at
|
|
838 // safepoints while holding them (_no_safepoint_check_flag). While it
|
|
839 // seems as though this could increase the time to reach a safepoint
|
|
840 // (or at least increase the mean, if not the variance), the latter
|
|
841 // approach might make for a cleaner, more maintainable JVM design.
|
|
842 //
|
|
843 // Sneaking is vile and reprehensible and should be excised at the 1st
|
|
844 // opportunity. It's possible that the need for sneaking could be obviated
|
|
845 // as follows. Currently, a thread might (a) while TBIVM, call pthread_mutex_lock
|
|
846 // or ILock() thus acquiring the "physical" lock underlying Monitor/Mutex.
|
|
847 // (b) stall at the TBIVM exit point as a safepoint is in effect. Critically,
|
|
848 // it'll stall at the TBIVM reentry state transition after having acquired the
|
|
849 // underlying lock, but before having set _owner and having entered the actual
|
|
850 // critical section. The lock-sneaking facility leverages that fact and allowed the
|
|
851 // VM thread to logically acquire locks that had already be physically locked by mutators
|
|
852 // but where mutators were known blocked by the reentry thread state transition.
|
|
853 //
|
|
854 // If we were to modify the Monitor-Mutex so that TBIVM state transitions tightly
|
|
855 // wrapped calls to park(), then we could likely do away with sneaking. We'd
|
|
856 // decouple lock acquisition and parking. The critical invariant to eliminating
|
|
857 // sneaking is to ensure that we never "physically" acquire the lock while TBIVM.
|
|
858 // An easy way to accomplish this is to wrap the park calls in a narrow TBIVM jacket.
|
|
859 // One difficulty with this approach is that the TBIVM wrapper could recurse and
|
|
860 // call lock() deep from within a lock() call, while the MutexEvent was already enqueued.
|
|
861 // Using a stack (N=2 at minimum) of ParkEvents would take care of that problem.
|
|
862 //
|
|
863 // But of course the proper ultimate approach is to avoid schemes that require explicit
|
|
864 // sneaking or dependence on any any clever invariants or subtle implementation properties
|
|
865 // of Mutex-Monitor and instead directly address the underlying design flaw.
|
|
866
|
|
867 void Monitor::lock (Thread * Self) {
|
|
868 #ifdef CHECK_UNHANDLED_OOPS
|
|
869 // Clear unhandled oops so we get a crash right away. Only clear for non-vm
|
|
870 // or GC threads.
|
|
871 if (Self->is_Java_thread()) {
|
|
872 Self->clear_unhandled_oops();
|
|
873 }
|
|
874 #endif // CHECK_UNHANDLED_OOPS
|
|
875
|
|
876 debug_only(check_prelock_state(Self));
|
|
877 assert (_owner != Self , "invariant") ;
|
|
878 assert (_OnDeck != Self->_MutexEvent, "invariant") ;
|
|
879
|
|
880 if (TryFast()) {
|
|
881 Exeunt:
|
|
882 assert (ILocked(), "invariant") ;
|
|
883 assert (owner() == NULL, "invariant");
|
|
884 set_owner (Self);
|
|
885 return ;
|
|
886 }
|
|
887
|
|
888 // The lock is contended ...
|
|
889
|
|
890 bool can_sneak = Self->is_VM_thread() && SafepointSynchronize::is_at_safepoint();
|
|
891 if (can_sneak && _owner == NULL) {
|
|
892 // a java thread has locked the lock but has not entered the
|
|
893 // critical region -- let's just pretend we've locked the lock
|
|
894 // and go on. we note this with _snuck so we can also
|
|
895 // pretend to unlock when the time comes.
|
|
896 _snuck = true;
|
|
897 goto Exeunt ;
|
|
898 }
|
|
899
|
|
900 // Try a brief spin to avoid passing thru thread state transition ...
|
|
901 if (TrySpin (Self)) goto Exeunt ;
|
|
902
|
|
903 check_block_state(Self);
|
|
904 if (Self->is_Java_thread()) {
|
|
905 // Horribile dictu - we suffer through a state transition
|
|
906 assert(rank() > Mutex::special, "Potential deadlock with special or lesser rank mutex");
|
|
907 ThreadBlockInVM tbivm ((JavaThread *) Self) ;
|
|
908 ILock (Self) ;
|
|
909 } else {
|
|
910 // Mirabile dictu
|
|
911 ILock (Self) ;
|
|
912 }
|
|
913 goto Exeunt ;
|
|
914 }
|
|
915
|
|
916 void Monitor::lock() {
|
|
917 this->lock(Thread::current());
|
|
918 }
|
|
919
|
|
920 // Lock without safepoint check - a degenerate variant of lock().
|
|
921 // Should ONLY be used by safepoint code and other code
|
|
922 // that is guaranteed not to block while running inside the VM. If this is called with
|
|
923 // thread state set to be in VM, the safepoint synchronization code will deadlock!
|
|
924
|
|
925 void Monitor::lock_without_safepoint_check (Thread * Self) {
|
|
926 assert (_owner != Self, "invariant") ;
|
|
927 ILock (Self) ;
|
|
928 assert (_owner == NULL, "invariant");
|
|
929 set_owner (Self);
|
|
930 }
|
|
931
|
|
932 void Monitor::lock_without_safepoint_check () {
|
|
933 lock_without_safepoint_check (Thread::current()) ;
|
|
934 }
|
|
935
|
|
936
|
|
937 // Returns true if thread succeceed [sic] in grabbing the lock, otherwise false.
|
|
938
|
|
939 bool Monitor::try_lock() {
|
|
940 Thread * const Self = Thread::current();
|
|
941 debug_only(check_prelock_state(Self));
|
|
942 // assert(!thread->is_inside_signal_handler(), "don't lock inside signal handler");
|
|
943
|
|
944 // Special case, where all Java threads are stopped.
|
|
945 // The lock may have been acquired but _owner is not yet set.
|
|
946 // In that case the VM thread can safely grab the lock.
|
|
947 // It strikes me this should appear _after the TryLock() fails, below.
|
|
948 bool can_sneak = Self->is_VM_thread() && SafepointSynchronize::is_at_safepoint();
|
|
949 if (can_sneak && _owner == NULL) {
|
|
950 set_owner(Self); // Do not need to be atomic, since we are at a safepoint
|
|
951 _snuck = true;
|
|
952 return true;
|
|
953 }
|
|
954
|
|
955 if (TryLock()) {
|
|
956 // We got the lock
|
|
957 assert (_owner == NULL, "invariant");
|
|
958 set_owner (Self);
|
|
959 return true;
|
|
960 }
|
|
961 return false;
|
|
962 }
|
|
963
|
|
964 void Monitor::unlock() {
|
|
965 assert (_owner == Thread::current(), "invariant") ;
|
|
966 assert (_OnDeck != Thread::current()->_MutexEvent , "invariant") ;
|
|
967 set_owner (NULL) ;
|
|
968 if (_snuck) {
|
|
969 assert(SafepointSynchronize::is_at_safepoint() && Thread::current()->is_VM_thread(), "sneak");
|
|
970 _snuck = false;
|
|
971 return ;
|
|
972 }
|
|
973 IUnlock (false) ;
|
|
974 }
|
|
975
|
|
976 // Yet another degenerate version of Monitor::lock() or lock_without_safepoint_check()
|
|
977 // jvm_raw_lock() and _unlock() can be called by non-Java threads via JVM_RawMonitorEnter.
|
|
978 //
|
|
979 // There's no expectation that JVM_RawMonitors will interoperate properly with the native
|
|
980 // Mutex-Monitor constructs. We happen to implement JVM_RawMonitors in terms of
|
|
981 // native Mutex-Monitors simply as a matter of convenience. A simple abstraction layer
|
|
982 // over a pthread_mutex_t would work equally as well, but require more platform-specific
|
|
983 // code -- a "PlatformMutex". Alternatively, a simply layer over muxAcquire-muxRelease
|
|
984 // would work too.
|
|
985 //
|
|
986 // Since the caller might be a foreign thread, we don't necessarily have a Thread.MutexEvent
|
|
987 // instance available. Instead, we transiently allocate a ParkEvent on-demand if
|
|
988 // we encounter contention. That ParkEvent remains associated with the thread
|
|
989 // until it manages to acquire the lock, at which time we return the ParkEvent
|
|
990 // to the global ParkEvent free list. This is correct and suffices for our purposes.
|
|
991 //
|
|
992 // Beware that the original jvm_raw_unlock() had a "_snuck" test but that
|
|
993 // jvm_raw_lock() didn't have the corresponding test. I suspect that's an
|
|
994 // oversight, but I've replicated the original suspect logic in the new code ...
|
|
995
|
|
996 void Monitor::jvm_raw_lock() {
|
|
997 assert(rank() == native, "invariant");
|
|
998
|
|
999 if (TryLock()) {
|
|
1000 Exeunt:
|
|
1001 assert (ILocked(), "invariant") ;
|
|
1002 assert (_owner == NULL, "invariant");
|
|
1003 // This can potentially be called by non-java Threads. Thus, the ThreadLocalStorage
|
|
1004 // might return NULL. Don't call set_owner since it will break on an NULL owner
|
|
1005 // Consider installing a non-null "ANON" distinguished value instead of just NULL.
|
|
1006 _owner = ThreadLocalStorage::thread();
|
|
1007 return ;
|
|
1008 }
|
|
1009
|
|
1010 if (TrySpin(NULL)) goto Exeunt ;
|
|
1011
|
|
1012 // slow-path - apparent contention
|
|
1013 // Allocate a ParkEvent for transient use.
|
|
1014 // The ParkEvent remains associated with this thread until
|
|
1015 // the time the thread manages to acquire the lock.
|
|
1016 ParkEvent * const ESelf = ParkEvent::Allocate(NULL) ;
|
|
1017 ESelf->reset() ;
|
|
1018 OrderAccess::storeload() ;
|
|
1019
|
|
1020 // Either Enqueue Self on cxq or acquire the outer lock.
|
|
1021 if (AcquireOrPush (ESelf)) {
|
|
1022 ParkEvent::Release (ESelf) ; // surrender the ParkEvent
|
|
1023 goto Exeunt ;
|
|
1024 }
|
|
1025
|
|
1026 // At any given time there is at most one ondeck thread.
|
|
1027 // ondeck implies not resident on cxq and not resident on EntryList
|
|
1028 // Only the OnDeck thread can try to acquire -- contended for -- the lock.
|
|
1029 // CONSIDER: use Self->OnDeck instead of m->OnDeck.
|
|
1030 for (;;) {
|
|
1031 if (_OnDeck == ESelf && TrySpin(NULL)) break ;
|
|
1032 ParkCommon (ESelf, 0) ;
|
|
1033 }
|
|
1034
|
|
1035 assert (_OnDeck == ESelf, "invariant") ;
|
|
1036 _OnDeck = NULL ;
|
|
1037 ParkEvent::Release (ESelf) ; // surrender the ParkEvent
|
|
1038 goto Exeunt ;
|
|
1039 }
|
|
1040
|
|
1041 void Monitor::jvm_raw_unlock() {
|
|
1042 // Nearly the same as Monitor::unlock() ...
|
|
1043 // directly set _owner instead of using set_owner(null)
|
|
1044 _owner = NULL ;
|
|
1045 if (_snuck) { // ???
|
|
1046 assert(SafepointSynchronize::is_at_safepoint() && Thread::current()->is_VM_thread(), "sneak");
|
|
1047 _snuck = false;
|
|
1048 return ;
|
|
1049 }
|
|
1050 IUnlock(false) ;
|
|
1051 }
|
|
1052
|
|
1053 bool Monitor::wait(bool no_safepoint_check, long timeout, bool as_suspend_equivalent) {
|
|
1054 Thread * const Self = Thread::current() ;
|
|
1055 assert (_owner == Self, "invariant") ;
|
|
1056 assert (ILocked(), "invariant") ;
|
|
1057
|
|
1058 // as_suspend_equivalent logically implies !no_safepoint_check
|
|
1059 guarantee (!as_suspend_equivalent || !no_safepoint_check, "invariant") ;
|
|
1060 // !no_safepoint_check logically implies java_thread
|
|
1061 guarantee (no_safepoint_check || Self->is_Java_thread(), "invariant") ;
|
|
1062
|
|
1063 #ifdef ASSERT
|
|
1064 Monitor * least = get_least_ranked_lock_besides_this(Self->owned_locks());
|
|
1065 assert(least != this, "Specification of get_least_... call above");
|
|
1066 if (least != NULL && least->rank() <= special) {
|
|
1067 tty->print("Attempting to wait on monitor %s/%d while holding"
|
|
1068 " lock %s/%d -- possible deadlock",
|
|
1069 name(), rank(), least->name(), least->rank());
|
|
1070 assert(false, "Shouldn't block(wait) while holding a lock of rank special");
|
|
1071 }
|
|
1072 #endif // ASSERT
|
|
1073
|
|
1074 int wait_status ;
|
|
1075 // conceptually set the owner to NULL in anticipation of
|
|
1076 // abdicating the lock in wait
|
|
1077 set_owner(NULL);
|
|
1078 if (no_safepoint_check) {
|
|
1079 wait_status = IWait (Self, timeout) ;
|
|
1080 } else {
|
|
1081 assert (Self->is_Java_thread(), "invariant") ;
|
|
1082 JavaThread *jt = (JavaThread *)Self;
|
|
1083
|
|
1084 // Enter safepoint region - ornate and Rococo ...
|
|
1085 ThreadBlockInVM tbivm(jt);
|
|
1086 OSThreadWaitState osts(Self->osthread(), false /* not Object.wait() */);
|
|
1087
|
|
1088 if (as_suspend_equivalent) {
|
|
1089 jt->set_suspend_equivalent();
|
|
1090 // cleared by handle_special_suspend_equivalent_condition() or
|
|
1091 // java_suspend_self()
|
|
1092 }
|
|
1093
|
|
1094 wait_status = IWait (Self, timeout) ;
|
|
1095
|
|
1096 // were we externally suspended while we were waiting?
|
|
1097 if (as_suspend_equivalent && jt->handle_special_suspend_equivalent_condition()) {
|
|
1098 // Our event wait has finished and we own the lock, but
|
|
1099 // while we were waiting another thread suspended us. We don't
|
|
1100 // want to hold the lock while suspended because that
|
|
1101 // would surprise the thread that suspended us.
|
|
1102 assert (ILocked(), "invariant") ;
|
|
1103 IUnlock (true) ;
|
|
1104 jt->java_suspend_self();
|
|
1105 ILock (Self) ;
|
|
1106 assert (ILocked(), "invariant") ;
|
|
1107 }
|
|
1108 }
|
|
1109
|
|
1110 // Conceptually reestablish ownership of the lock.
|
|
1111 // The "real" lock -- the LockByte -- was reacquired by IWait().
|
|
1112 assert (ILocked(), "invariant") ;
|
|
1113 assert (_owner == NULL, "invariant") ;
|
|
1114 set_owner (Self) ;
|
|
1115 return wait_status != 0 ; // return true IFF timeout
|
|
1116 }
|
|
1117
|
|
1118 Monitor::~Monitor() {
|
|
1119 assert ((UNS(_owner)|UNS(_LockWord.FullWord)|UNS(_EntryList)|UNS(_WaitSet)|UNS(_OnDeck)) == 0, "") ;
|
|
1120 }
|
|
1121
|
|
1122 void Monitor::ClearMonitor (Monitor * m) {
|
|
1123 m->_owner = NULL ;
|
|
1124 m->_snuck = false ;
|
|
1125 m->_name = "UNKNOWN" ;
|
|
1126 m->_LockWord.FullWord = 0 ;
|
|
1127 m->_EntryList = NULL ;
|
|
1128 m->_OnDeck = NULL ;
|
|
1129 m->_WaitSet = NULL ;
|
|
1130 m->_WaitLock[0] = 0 ;
|
|
1131 }
|
|
1132
|
|
1133 Monitor::Monitor() { ClearMonitor(this); }
|
|
1134
|
|
1135 Monitor::Monitor (int Rank, const char * name, bool allow_vm_block) {
|
|
1136 ClearMonitor (this) ;
|
|
1137 #ifdef ASSERT
|
|
1138 _allow_vm_block = allow_vm_block;
|
|
1139 _rank = Rank ;
|
|
1140 #endif
|
|
1141 }
|
|
1142
|
|
1143 Mutex::~Mutex() {
|
|
1144 assert ((UNS(_owner)|UNS(_LockWord.FullWord)|UNS(_EntryList)|UNS(_WaitSet)|UNS(_OnDeck)) == 0, "") ;
|
|
1145 }
|
|
1146
|
|
1147 Mutex::Mutex (int Rank, const char * name, bool allow_vm_block) {
|
|
1148 ClearMonitor ((Monitor *) this) ;
|
|
1149 #ifdef ASSERT
|
|
1150 _allow_vm_block = allow_vm_block;
|
|
1151 _rank = Rank ;
|
|
1152 #endif
|
|
1153 }
|
|
1154
|
|
1155 bool Monitor::owned_by_self() const {
|
|
1156 bool ret = _owner == Thread::current();
|
|
1157 assert (!ret || _LockWord.Bytes[_LSBINDEX] != 0, "invariant") ;
|
|
1158 return ret;
|
|
1159 }
|
|
1160
|
|
1161 void Monitor::print_on_error(outputStream* st) const {
|
|
1162 st->print("[" PTR_FORMAT, this);
|
|
1163 st->print("] %s", _name);
|
|
1164 st->print(" - owner thread: " PTR_FORMAT, _owner);
|
|
1165 }
|
|
1166
|
|
1167
|
|
1168
|
|
1169
|
|
1170 // ----------------------------------------------------------------------------------
|
|
1171 // Non-product code
|
|
1172
|
|
1173 #ifndef PRODUCT
|
|
1174 void Monitor::print_on(outputStream* st) const {
|
|
1175 st->print_cr("Mutex: [0x%lx/0x%lx] %s - owner: 0x%lx", this, _LockWord.FullWord, _name, _owner);
|
|
1176 }
|
|
1177 #endif
|
|
1178
|
|
1179 #ifndef PRODUCT
|
|
1180 #ifdef ASSERT
|
|
1181 Monitor * Monitor::get_least_ranked_lock(Monitor * locks) {
|
|
1182 Monitor *res, *tmp;
|
|
1183 for (res = tmp = locks; tmp != NULL; tmp = tmp->next()) {
|
|
1184 if (tmp->rank() < res->rank()) {
|
|
1185 res = tmp;
|
|
1186 }
|
|
1187 }
|
|
1188 if (!SafepointSynchronize::is_at_safepoint()) {
|
|
1189 // In this case, we expect the held locks to be
|
|
1190 // in increasing rank order (modulo any native ranks)
|
|
1191 for (tmp = locks; tmp != NULL; tmp = tmp->next()) {
|
|
1192 if (tmp->next() != NULL) {
|
|
1193 assert(tmp->rank() == Mutex::native ||
|
|
1194 tmp->rank() <= tmp->next()->rank(), "mutex rank anomaly?");
|
|
1195 }
|
|
1196 }
|
|
1197 }
|
|
1198 return res;
|
|
1199 }
|
|
1200
|
|
1201 Monitor* Monitor::get_least_ranked_lock_besides_this(Monitor* locks) {
|
|
1202 Monitor *res, *tmp;
|
|
1203 for (res = NULL, tmp = locks; tmp != NULL; tmp = tmp->next()) {
|
|
1204 if (tmp != this && (res == NULL || tmp->rank() < res->rank())) {
|
|
1205 res = tmp;
|
|
1206 }
|
|
1207 }
|
|
1208 if (!SafepointSynchronize::is_at_safepoint()) {
|
|
1209 // In this case, we expect the held locks to be
|
|
1210 // in increasing rank order (modulo any native ranks)
|
|
1211 for (tmp = locks; tmp != NULL; tmp = tmp->next()) {
|
|
1212 if (tmp->next() != NULL) {
|
|
1213 assert(tmp->rank() == Mutex::native ||
|
|
1214 tmp->rank() <= tmp->next()->rank(), "mutex rank anomaly?");
|
|
1215 }
|
|
1216 }
|
|
1217 }
|
|
1218 return res;
|
|
1219 }
|
|
1220
|
|
1221
|
|
1222 bool Monitor::contains(Monitor* locks, Monitor * lock) {
|
|
1223 for (; locks != NULL; locks = locks->next()) {
|
|
1224 if (locks == lock)
|
|
1225 return true;
|
|
1226 }
|
|
1227 return false;
|
|
1228 }
|
|
1229 #endif
|
|
1230
|
|
1231 // Called immediately after lock acquisition or release as a diagnostic
|
|
1232 // to track the lock-set of the thread and test for rank violations that
|
|
1233 // might indicate exposure to deadlock.
|
|
1234 // Rather like an EventListener for _owner (:>).
|
|
1235
|
|
1236 void Monitor::set_owner_implementation(Thread *new_owner) {
|
|
1237 // This function is solely responsible for maintaining
|
|
1238 // and checking the invariant that threads and locks
|
|
1239 // are in a 1/N relation, with some some locks unowned.
|
|
1240 // It uses the Mutex::_owner, Mutex::_next, and
|
|
1241 // Thread::_owned_locks fields, and no other function
|
|
1242 // changes those fields.
|
|
1243 // It is illegal to set the mutex from one non-NULL
|
|
1244 // owner to another--it must be owned by NULL as an
|
|
1245 // intermediate state.
|
|
1246
|
|
1247 if (new_owner != NULL) {
|
|
1248 // the thread is acquiring this lock
|
|
1249
|
|
1250 assert(new_owner == Thread::current(), "Should I be doing this?");
|
|
1251 assert(_owner == NULL, "setting the owner thread of an already owned mutex");
|
|
1252 _owner = new_owner; // set the owner
|
|
1253
|
|
1254 // link "this" into the owned locks list
|
|
1255
|
|
1256 #ifdef ASSERT // Thread::_owned_locks is under the same ifdef
|
|
1257 Monitor* locks = get_least_ranked_lock(new_owner->owned_locks());
|
|
1258 // Mutex::set_owner_implementation is a friend of Thread
|
|
1259
|
|
1260 assert(this->rank() >= 0, "bad lock rank");
|
|
1261
|
|
1262 if (LogMultipleMutexLocking && locks != NULL) {
|
|
1263 Events::log("thread " INTPTR_FORMAT " locks %s, already owns %s", new_owner, name(), locks->name());
|
|
1264 }
|
|
1265
|
|
1266 // Deadlock avoidance rules require us to acquire Mutexes only in
|
|
1267 // a global total order. For example m1 is the lowest ranked mutex
|
|
1268 // that the thread holds and m2 is the mutex the thread is trying
|
|
1269 // to acquire, then deadlock avoidance rules require that the rank
|
|
1270 // of m2 be less than the rank of m1.
|
|
1271 // The rank Mutex::native is an exception in that it is not subject
|
|
1272 // to the verification rules.
|
|
1273 // Here are some further notes relating to mutex acquisition anomalies:
|
|
1274 // . under Solaris, the interrupt lock gets acquired when doing
|
|
1275 // profiling, so any lock could be held.
|
|
1276 // . it is also ok to acquire Safepoint_lock at the very end while we
|
|
1277 // already hold Terminator_lock - may happen because of periodic safepoints
|
|
1278 if (this->rank() != Mutex::native &&
|
|
1279 this->rank() != Mutex::suspend_resume &&
|
|
1280 locks != NULL && locks->rank() <= this->rank() &&
|
|
1281 !SafepointSynchronize::is_at_safepoint() &&
|
|
1282 this != Interrupt_lock && this != ProfileVM_lock &&
|
|
1283 !(this == Safepoint_lock && contains(locks, Terminator_lock) &&
|
|
1284 SafepointSynchronize::is_synchronizing())) {
|
|
1285 new_owner->print_owned_locks();
|
|
1286 fatal4("acquiring lock %s/%d out of order with lock %s/%d -- possible deadlock",
|
|
1287 this->name(), this->rank(), locks->name(), locks->rank());
|
|
1288 }
|
|
1289
|
|
1290 this->_next = new_owner->_owned_locks;
|
|
1291 new_owner->_owned_locks = this;
|
|
1292 #endif
|
|
1293
|
|
1294 } else {
|
|
1295 // the thread is releasing this lock
|
|
1296
|
|
1297 Thread* old_owner = _owner;
|
|
1298 debug_only(_last_owner = old_owner);
|
|
1299
|
|
1300 assert(old_owner != NULL, "removing the owner thread of an unowned mutex");
|
|
1301 assert(old_owner == Thread::current(), "removing the owner thread of an unowned mutex");
|
|
1302
|
|
1303 _owner = NULL; // set the owner
|
|
1304
|
|
1305 #ifdef ASSERT
|
|
1306 Monitor *locks = old_owner->owned_locks();
|
|
1307
|
|
1308 if (LogMultipleMutexLocking && locks != this) {
|
|
1309 Events::log("thread " INTPTR_FORMAT " unlocks %s, still owns %s", old_owner, this->name(), locks->name());
|
|
1310 }
|
|
1311
|
|
1312 // remove "this" from the owned locks list
|
|
1313
|
|
1314 Monitor *prev = NULL;
|
|
1315 bool found = false;
|
|
1316 for (; locks != NULL; prev = locks, locks = locks->next()) {
|
|
1317 if (locks == this) {
|
|
1318 found = true;
|
|
1319 break;
|
|
1320 }
|
|
1321 }
|
|
1322 assert(found, "Removing a lock not owned");
|
|
1323 if (prev == NULL) {
|
|
1324 old_owner->_owned_locks = _next;
|
|
1325 } else {
|
|
1326 prev->_next = _next;
|
|
1327 }
|
|
1328 _next = NULL;
|
|
1329 #endif
|
|
1330 }
|
|
1331 }
|
|
1332
|
|
1333
|
|
1334 // Factored out common sanity checks for locking mutex'es. Used by lock() and try_lock()
|
|
1335 void Monitor::check_prelock_state(Thread *thread) {
|
|
1336 assert((!thread->is_Java_thread() || ((JavaThread *)thread)->thread_state() == _thread_in_vm)
|
|
1337 || rank() == Mutex::special, "wrong thread state for using locks");
|
|
1338 if (StrictSafepointChecks) {
|
|
1339 if (thread->is_VM_thread() && !allow_vm_block()) {
|
|
1340 fatal1("VM thread using lock %s (not allowed to block on)", name());
|
|
1341 }
|
|
1342 debug_only(if (rank() != Mutex::special) \
|
|
1343 thread->check_for_valid_safepoint_state(false);)
|
|
1344 }
|
|
1345 }
|
|
1346
|
|
1347 void Monitor::check_block_state(Thread *thread) {
|
|
1348 if (!_allow_vm_block && thread->is_VM_thread()) {
|
|
1349 warning("VM thread blocked on lock");
|
|
1350 print();
|
|
1351 BREAKPOINT;
|
|
1352 }
|
|
1353 assert(_owner != thread, "deadlock: blocking on monitor owned by current thread");
|
|
1354 }
|
|
1355
|
|
1356 #endif // PRODUCT
|