1 /*
2 * Copyright (c) 2003, 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 # include "incls/_precompiled.incl"
26 # include "incls/_jvmtiRawMonitor.cpp.incl"
27
28 GrowableArray<JvmtiRawMonitor*> *JvmtiPendingMonitors::_monitors = new (ResourceObj::C_HEAP) GrowableArray<JvmtiRawMonitor*>(1,true);
29
30 void JvmtiPendingMonitors::transition_raw_monitors() {
31 assert((Threads::number_of_threads()==1),
32 "Java thread has not created yet or more than one java thread \
33 is running. Raw monitor transition will not work");
34 JavaThread *current_java_thread = JavaThread::current();
35 assert(current_java_thread->thread_state() == _thread_in_vm, "Must be in vm");
36 {
37 ThreadBlockInVM __tbivm(current_java_thread);
38 for(int i=0; i< count(); i++) {
39 JvmtiRawMonitor *rmonitor = monitors()->at(i);
40 int r = rmonitor->raw_enter(current_java_thread);
41 assert(r == ObjectMonitor::OM_OK, "raw_enter should have worked");
42 }
43 }
44 // pending monitors are converted to real monitor so delete them all.
45 dispose();
46 }
47
48 //
49 // class JvmtiRawMonitor
50 //
51
52 JvmtiRawMonitor::JvmtiRawMonitor(const char *name) {
53 #ifdef ASSERT
54 _name = strcpy(NEW_C_HEAP_ARRAY(char, strlen(name) + 1), name);
55 #else
56 _name = NULL;
57 #endif
58 _magic = JVMTI_RM_MAGIC;
59 }
60
61 JvmtiRawMonitor::~JvmtiRawMonitor() {
62 #ifdef ASSERT
63 FreeHeap(_name);
64 #endif
65 _magic = 0;
66 }
67
68
69 bool
70 JvmtiRawMonitor::is_valid() {
71 int value = 0;
72
73 // This object might not be a JvmtiRawMonitor so we can't assume
74 // the _magic field is properly aligned. Get the value in a safe
75 // way and then check against JVMTI_RM_MAGIC.
76
77 switch (sizeof(_magic)) {
78 case 2:
79 value = Bytes::get_native_u2((address)&_magic);
80 break;
81
82 case 4:
83 value = Bytes::get_native_u4((address)&_magic);
84 break;
85
86 case 8:
87 value = Bytes::get_native_u8((address)&_magic);
88 break;
89
90 default:
91 guarantee(false, "_magic field is an unexpected size");
92 }
93
94 return value == JVMTI_RM_MAGIC;
95 }
96
97 // -------------------------------------------------------------------------
98 // The raw monitor subsystem is entirely distinct from normal
99 // java-synchronization or jni-synchronization. raw monitors are not
100 // associated with objects. They can be implemented in any manner
101 // that makes sense. The original implementors decided to piggy-back
102 // the raw-monitor implementation on the existing Java objectMonitor mechanism.
103 // This flaw needs to fixed. We should reimplement raw monitors as sui-generis.
104 // Specifically, we should not implement raw monitors via java monitors.
105 // Time permitting, we should disentangle and deconvolve the two implementations
106 // and move the resulting raw monitor implementation over to the JVMTI directories.
107 // Ideally, the raw monitor implementation would be built on top of
108 // park-unpark and nothing else.
109 //
110 // raw monitors are used mainly by JVMTI
111 // The raw monitor implementation borrows the ObjectMonitor structure,
112 // but the operators are degenerate and extremely simple.
113 //
114 // Mixed use of a single objectMonitor instance -- as both a raw monitor
115 // and a normal java monitor -- is not permissible.
116 //
117 // Note that we use the single RawMonitor_lock to protect queue operations for
118 // _all_ raw monitors. This is a scalability impediment, but since raw monitor usage
119 // is deprecated and rare, this is not of concern. The RawMonitor_lock can not
120 // be held indefinitely. The critical sections must be short and bounded.
121 //
122 // -------------------------------------------------------------------------
123
124 int JvmtiRawMonitor::SimpleEnter (Thread * Self) {
125 for (;;) {
126 if (Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) {
127 return OS_OK ;
128 }
129
130 ObjectWaiter Node (Self) ;
131 Self->_ParkEvent->reset() ; // strictly optional
132 Node.TState = ObjectWaiter::TS_ENTER ;
133
134 RawMonitor_lock->lock_without_safepoint_check() ;
135 Node._next = _EntryList ;
136 _EntryList = &Node ;
137 OrderAccess::fence() ;
138 if (_owner == NULL && Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) {
139 _EntryList = Node._next ;
140 RawMonitor_lock->unlock() ;
141 return OS_OK ;
142 }
143 RawMonitor_lock->unlock() ;
144 while (Node.TState == ObjectWaiter::TS_ENTER) {
145 Self->_ParkEvent->park() ;
146 }
147 }
148 }
149
150 int JvmtiRawMonitor::SimpleExit (Thread * Self) {
151 guarantee (_owner == Self, "invariant") ;
152 OrderAccess::release_store_ptr (&_owner, NULL) ;
153 OrderAccess::fence() ;
154 if (_EntryList == NULL) return OS_OK ;
155 ObjectWaiter * w ;
156
157 RawMonitor_lock->lock_without_safepoint_check() ;
158 w = _EntryList ;
159 if (w != NULL) {
160 _EntryList = w->_next ;
161 }
162 RawMonitor_lock->unlock() ;
163 if (w != NULL) {
164 guarantee (w ->TState == ObjectWaiter::TS_ENTER, "invariant") ;
165 ParkEvent * ev = w->_event ;
166 w->TState = ObjectWaiter::TS_RUN ;
167 OrderAccess::fence() ;
168 ev->unpark() ;
169 }
170 return OS_OK ;
171 }
172
173 int JvmtiRawMonitor::SimpleWait (Thread * Self, jlong millis) {
174 guarantee (_owner == Self , "invariant") ;
175 guarantee (_recursions == 0, "invariant") ;
176
177 ObjectWaiter Node (Self) ;
178 Node._notified = 0 ;
179 Node.TState = ObjectWaiter::TS_WAIT ;
180
181 RawMonitor_lock->lock_without_safepoint_check() ;
182 Node._next = _WaitSet ;
183 _WaitSet = &Node ;
184 RawMonitor_lock->unlock() ;
185
186 SimpleExit (Self) ;
187 guarantee (_owner != Self, "invariant") ;
188
189 int ret = OS_OK ;
190 if (millis <= 0) {
191 Self->_ParkEvent->park();
192 } else {
193 ret = Self->_ParkEvent->park(millis);
194 }
195
196 // If thread still resides on the waitset then unlink it.
197 // Double-checked locking -- the usage is safe in this context
198 // as we TState is volatile and the lock-unlock operators are
199 // serializing (barrier-equivalent).
200
201 if (Node.TState == ObjectWaiter::TS_WAIT) {
202 RawMonitor_lock->lock_without_safepoint_check() ;
203 if (Node.TState == ObjectWaiter::TS_WAIT) {
204 // Simple O(n) unlink, but performance isn't critical here.
205 ObjectWaiter * p ;
206 ObjectWaiter * q = NULL ;
207 for (p = _WaitSet ; p != &Node; p = p->_next) {
208 q = p ;
209 }
210 guarantee (p == &Node, "invariant") ;
211 if (q == NULL) {
212 guarantee (p == _WaitSet, "invariant") ;
213 _WaitSet = p->_next ;
214 } else {
215 guarantee (p == q->_next, "invariant") ;
216 q->_next = p->_next ;
217 }
218 Node.TState = ObjectWaiter::TS_RUN ;
219 }
220 RawMonitor_lock->unlock() ;
221 }
222
223 guarantee (Node.TState == ObjectWaiter::TS_RUN, "invariant") ;
224 SimpleEnter (Self) ;
225
226 guarantee (_owner == Self, "invariant") ;
227 guarantee (_recursions == 0, "invariant") ;
228 return ret ;
229 }
230
231 int JvmtiRawMonitor::SimpleNotify (Thread * Self, bool All) {
232 guarantee (_owner == Self, "invariant") ;
233 if (_WaitSet == NULL) return OS_OK ;
234
235 // We have two options:
236 // A. Transfer the threads from the WaitSet to the EntryList
237 // B. Remove the thread from the WaitSet and unpark() it.
238 //
239 // We use (B), which is crude and results in lots of futile
240 // context switching. In particular (B) induces lots of contention.
241
242 ParkEvent * ev = NULL ; // consider using a small auto array ...
243 RawMonitor_lock->lock_without_safepoint_check() ;
244 for (;;) {
245 ObjectWaiter * w = _WaitSet ;
246 if (w == NULL) break ;
247 _WaitSet = w->_next ;
248 if (ev != NULL) { ev->unpark(); ev = NULL; }
249 ev = w->_event ;
250 OrderAccess::loadstore() ;
251 w->TState = ObjectWaiter::TS_RUN ;
252 OrderAccess::storeload();
253 if (!All) break ;
254 }
255 RawMonitor_lock->unlock() ;
256 if (ev != NULL) ev->unpark();
257 return OS_OK ;
258 }
259
260 // Any JavaThread will enter here with state _thread_blocked
261 int JvmtiRawMonitor::raw_enter(TRAPS) {
262 TEVENT (raw_enter) ;
263 void * Contended ;
264
265 // don't enter raw monitor if thread is being externally suspended, it will
266 // surprise the suspender if a "suspended" thread can still enter monitor
267 JavaThread * jt = (JavaThread *)THREAD;
268 if (THREAD->is_Java_thread()) {
269 jt->SR_lock()->lock_without_safepoint_check();
270 while (jt->is_external_suspend()) {
271 jt->SR_lock()->unlock();
272 jt->java_suspend_self();
273 jt->SR_lock()->lock_without_safepoint_check();
274 }
275 // guarded by SR_lock to avoid racing with new external suspend requests.
276 Contended = Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) ;
277 jt->SR_lock()->unlock();
278 } else {
279 Contended = Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) ;
280 }
281
282 if (Contended == THREAD) {
283 _recursions ++ ;
284 return OM_OK ;
285 }
286
287 if (Contended == NULL) {
288 guarantee (_owner == THREAD, "invariant") ;
289 guarantee (_recursions == 0, "invariant") ;
290 return OM_OK ;
291 }
292
293 THREAD->set_current_pending_monitor(this);
294
295 if (!THREAD->is_Java_thread()) {
296 // No other non-Java threads besides VM thread would acquire
297 // a raw monitor.
298 assert(THREAD->is_VM_thread(), "must be VM thread");
299 SimpleEnter (THREAD) ;
300 } else {
301 guarantee (jt->thread_state() == _thread_blocked, "invariant") ;
302 for (;;) {
303 jt->set_suspend_equivalent();
304 // cleared by handle_special_suspend_equivalent_condition() or
305 // java_suspend_self()
306 SimpleEnter (THREAD) ;
307
308 // were we externally suspended while we were waiting?
309 if (!jt->handle_special_suspend_equivalent_condition()) break ;
310
311 // This thread was externally suspended
312 //
313 // This logic isn't needed for JVMTI raw monitors,
314 // but doesn't hurt just in case the suspend rules change. This
315 // logic is needed for the JvmtiRawMonitor.wait() reentry phase.
316 // We have reentered the contended monitor, but while we were
317 // waiting another thread suspended us. We don't want to reenter
318 // the monitor while suspended because that would surprise the
319 // thread that suspended us.
320 //
321 // Drop the lock -
322 SimpleExit (THREAD) ;
323
324 jt->java_suspend_self();
325 }
326
327 assert(_owner == THREAD, "Fatal error with monitor owner!");
328 assert(_recursions == 0, "Fatal error with monitor recursions!");
329 }
330
331 THREAD->set_current_pending_monitor(NULL);
332 guarantee (_recursions == 0, "invariant") ;
333 return OM_OK;
334 }
335
336 // Used mainly for JVMTI raw monitor implementation
337 // Also used for JvmtiRawMonitor::wait().
338 int JvmtiRawMonitor::raw_exit(TRAPS) {
339 TEVENT (raw_exit) ;
340 if (THREAD != _owner) {
341 return OM_ILLEGAL_MONITOR_STATE;
342 }
343 if (_recursions > 0) {
344 --_recursions ;
345 return OM_OK ;
346 }
347
348 void * List = _EntryList ;
349 SimpleExit (THREAD) ;
350
351 return OM_OK;
352 }
353
354 // Used for JVMTI raw monitor implementation.
355 // All JavaThreads will enter here with state _thread_blocked
356
357 int JvmtiRawMonitor::raw_wait(jlong millis, bool interruptible, TRAPS) {
358 TEVENT (raw_wait) ;
359 if (THREAD != _owner) {
360 return OM_ILLEGAL_MONITOR_STATE;
361 }
362
363 // To avoid spurious wakeups we reset the parkevent -- This is strictly optional.
364 // The caller must be able to tolerate spurious returns from raw_wait().
365 THREAD->_ParkEvent->reset() ;
366 OrderAccess::fence() ;
367
368 // check interrupt event
369 if (interruptible && Thread::is_interrupted(THREAD, true)) {
370 return OM_INTERRUPTED;
371 }
372
373 intptr_t save = _recursions ;
374 _recursions = 0 ;
375 _waiters ++ ;
376 if (THREAD->is_Java_thread()) {
377 guarantee (((JavaThread *) THREAD)->thread_state() == _thread_blocked, "invariant") ;
378 ((JavaThread *)THREAD)->set_suspend_equivalent();
379 }
380 int rv = SimpleWait (THREAD, millis) ;
381 _recursions = save ;
382 _waiters -- ;
383
384 guarantee (THREAD == _owner, "invariant") ;
385 if (THREAD->is_Java_thread()) {
386 JavaThread * jSelf = (JavaThread *) THREAD ;
387 for (;;) {
388 if (!jSelf->handle_special_suspend_equivalent_condition()) break ;
389 SimpleExit (THREAD) ;
390 jSelf->java_suspend_self();
391 SimpleEnter (THREAD) ;
392 jSelf->set_suspend_equivalent() ;
393 }
394 }
395 guarantee (THREAD == _owner, "invariant") ;
396
397 if (interruptible && Thread::is_interrupted(THREAD, true)) {
398 return OM_INTERRUPTED;
399 }
400 return OM_OK ;
401 }
402
403 int JvmtiRawMonitor::raw_notify(TRAPS) {
404 TEVENT (raw_notify) ;
405 if (THREAD != _owner) {
406 return OM_ILLEGAL_MONITOR_STATE;
407 }
408 SimpleNotify (THREAD, false) ;
409 return OM_OK;
410 }
411
412 int JvmtiRawMonitor::raw_notifyAll(TRAPS) {
413 TEVENT (raw_notifyAll) ;
414 if (THREAD != _owner) {
415 return OM_ILLEGAL_MONITOR_STATE;
416 }
417 SimpleNotify (THREAD, true) ;
418 return OM_OK;
419 }
420