1 /*
2 * Copyright (c) 2003, 2010, 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 "precompiled.hpp"
26 #include "prims/jvmtiRawMonitor.hpp"
27 #include "runtime/interfaceSupport.hpp"
28 #include "runtime/thread.hpp"
29
30 GrowableArray<JvmtiRawMonitor*> *JvmtiPendingMonitors::_monitors = new (ResourceObj::C_HEAP) GrowableArray<JvmtiRawMonitor*>(1,true);
31
32 void JvmtiPendingMonitors::transition_raw_monitors() {
33 assert((Threads::number_of_threads()==1),
34 "Java thread has not created yet or more than one java thread \
35 is running. Raw monitor transition will not work");
36 JavaThread *current_java_thread = JavaThread::current();
37 assert(current_java_thread->thread_state() == _thread_in_vm, "Must be in vm");
38 {
39 ThreadBlockInVM __tbivm(current_java_thread);
40 for(int i=0; i< count(); i++) {
41 JvmtiRawMonitor *rmonitor = monitors()->at(i);
42 int r = rmonitor->raw_enter(current_java_thread);
43 assert(r == ObjectMonitor::OM_OK, "raw_enter should have worked");
44 }
45 }
46 // pending monitors are converted to real monitor so delete them all.
47 dispose();
48 }
49
50 //
51 // class JvmtiRawMonitor
52 //
53
54 JvmtiRawMonitor::JvmtiRawMonitor(const char *name) {
55 #ifdef ASSERT
56 _name = strcpy(NEW_C_HEAP_ARRAY(char, strlen(name) + 1), name);
57 #else
58 _name = NULL;
59 #endif
60 _magic = JVMTI_RM_MAGIC;
61 }
62
63 JvmtiRawMonitor::~JvmtiRawMonitor() {
64 #ifdef ASSERT
65 FreeHeap(_name);
66 #endif
67 _magic = 0;
68 }
69
70
71 bool
72 JvmtiRawMonitor::is_valid() {
73 int value = 0;
74
75 // This object might not be a JvmtiRawMonitor so we can't assume
76 // the _magic field is properly aligned. Get the value in a safe
77 // way and then check against JVMTI_RM_MAGIC.
78
79 switch (sizeof(_magic)) {
80 case 2:
81 value = Bytes::get_native_u2((address)&_magic);
82 break;
83
84 case 4:
85 value = Bytes::get_native_u4((address)&_magic);
86 break;
87
88 case 8:
89 value = Bytes::get_native_u8((address)&_magic);
90 break;
91
92 default:
93 guarantee(false, "_magic field is an unexpected size");
94 }
95
96 return value == JVMTI_RM_MAGIC;
97 }
98
99 // -------------------------------------------------------------------------
100 // The raw monitor subsystem is entirely distinct from normal
101 // java-synchronization or jni-synchronization. raw monitors are not
102 // associated with objects. They can be implemented in any manner
103 // that makes sense. The original implementors decided to piggy-back
104 // the raw-monitor implementation on the existing Java objectMonitor mechanism.
105 // This flaw needs to fixed. We should reimplement raw monitors as sui-generis.
106 // Specifically, we should not implement raw monitors via java monitors.
107 // Time permitting, we should disentangle and deconvolve the two implementations
108 // and move the resulting raw monitor implementation over to the JVMTI directories.
109 // Ideally, the raw monitor implementation would be built on top of
110 // park-unpark and nothing else.
111 //
112 // raw monitors are used mainly by JVMTI
113 // The raw monitor implementation borrows the ObjectMonitor structure,
114 // but the operators are degenerate and extremely simple.
115 //
116 // Mixed use of a single objectMonitor instance -- as both a raw monitor
117 // and a normal java monitor -- is not permissible.
118 //
119 // Note that we use the single RawMonitor_lock to protect queue operations for
120 // _all_ raw monitors. This is a scalability impediment, but since raw monitor usage
121 // is deprecated and rare, this is not of concern. The RawMonitor_lock can not
122 // be held indefinitely. The critical sections must be short and bounded.
123 //
124 // -------------------------------------------------------------------------
125
126 int JvmtiRawMonitor::SimpleEnter (Thread * Self) {
127 for (;;) {
128 if (Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) {
129 return OS_OK ;
130 }
131
132 ObjectWaiter Node (Self) ;
133 Self->_ParkEvent->reset() ; // strictly optional
134 Node.TState = ObjectWaiter::TS_ENTER ;
135
136 RawMonitor_lock->lock_without_safepoint_check() ;
137 Node._next = _EntryList ;
138 _EntryList = &Node ;
139 OrderAccess::fence() ;
140 if (_owner == NULL && Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) {
141 _EntryList = Node._next ;
142 RawMonitor_lock->unlock() ;
143 return OS_OK ;
144 }
145 RawMonitor_lock->unlock() ;
146 while (Node.TState == ObjectWaiter::TS_ENTER) {
147 Self->_ParkEvent->park() ;
148 }
149 }
150 }
151
152 int JvmtiRawMonitor::SimpleExit (Thread * Self) {
153 guarantee (_owner == Self, "invariant") ;
154 OrderAccess::release_store_ptr (&_owner, NULL) ;
155 OrderAccess::fence() ;
156 if (_EntryList == NULL) return OS_OK ;
157 ObjectWaiter * w ;
158
159 RawMonitor_lock->lock_without_safepoint_check() ;
160 w = _EntryList ;
161 if (w != NULL) {
162 _EntryList = w->_next ;
163 }
164 RawMonitor_lock->unlock() ;
165 if (w != NULL) {
166 guarantee (w ->TState == ObjectWaiter::TS_ENTER, "invariant") ;
167 ParkEvent * ev = w->_event ;
168 w->TState = ObjectWaiter::TS_RUN ;
169 OrderAccess::fence() ;
170 ev->unpark() ;
171 }
172 return OS_OK ;
173 }
174
175 int JvmtiRawMonitor::SimpleWait (Thread * Self, jlong millis) {
176 guarantee (_owner == Self , "invariant") ;
177 guarantee (_recursions == 0, "invariant") ;
178
179 ObjectWaiter Node (Self) ;
180 Node._notified = 0 ;
181 Node.TState = ObjectWaiter::TS_WAIT ;
182
183 RawMonitor_lock->lock_without_safepoint_check() ;
184 Node._next = _WaitSet ;
185 _WaitSet = &Node ;
186 RawMonitor_lock->unlock() ;
187
188 SimpleExit (Self) ;
189 guarantee (_owner != Self, "invariant") ;
190
191 int ret = OS_OK ;
192 if (millis <= 0) {
193 Self->_ParkEvent->park();
194 } else {
195 ret = Self->_ParkEvent->park(millis);
196 }
197
198 // If thread still resides on the waitset then unlink it.
199 // Double-checked locking -- the usage is safe in this context
200 // as we TState is volatile and the lock-unlock operators are
201 // serializing (barrier-equivalent).
202
203 if (Node.TState == ObjectWaiter::TS_WAIT) {
204 RawMonitor_lock->lock_without_safepoint_check() ;
205 if (Node.TState == ObjectWaiter::TS_WAIT) {
206 // Simple O(n) unlink, but performance isn't critical here.
207 ObjectWaiter * p ;
208 ObjectWaiter * q = NULL ;
209 for (p = _WaitSet ; p != &Node; p = p->_next) {
210 q = p ;
211 }
212 guarantee (p == &Node, "invariant") ;
213 if (q == NULL) {
214 guarantee (p == _WaitSet, "invariant") ;
215 _WaitSet = p->_next ;
216 } else {
217 guarantee (p == q->_next, "invariant") ;
218 q->_next = p->_next ;
219 }
220 Node.TState = ObjectWaiter::TS_RUN ;
221 }
222 RawMonitor_lock->unlock() ;
223 }
224
225 guarantee (Node.TState == ObjectWaiter::TS_RUN, "invariant") ;
226 SimpleEnter (Self) ;
227
228 guarantee (_owner == Self, "invariant") ;
229 guarantee (_recursions == 0, "invariant") ;
230 return ret ;
231 }
232
233 int JvmtiRawMonitor::SimpleNotify (Thread * Self, bool All) {
234 guarantee (_owner == Self, "invariant") ;
235 if (_WaitSet == NULL) return OS_OK ;
236
237 // We have two options:
238 // A. Transfer the threads from the WaitSet to the EntryList
239 // B. Remove the thread from the WaitSet and unpark() it.
240 //
241 // We use (B), which is crude and results in lots of futile
242 // context switching. In particular (B) induces lots of contention.
243
244 ParkEvent * ev = NULL ; // consider using a small auto array ...
245 RawMonitor_lock->lock_without_safepoint_check() ;
246 for (;;) {
247 ObjectWaiter * w = _WaitSet ;
248 if (w == NULL) break ;
249 _WaitSet = w->_next ;
250 if (ev != NULL) { ev->unpark(); ev = NULL; }
251 ev = w->_event ;
252 OrderAccess::loadstore() ;
253 w->TState = ObjectWaiter::TS_RUN ;
254 OrderAccess::storeload();
255 if (!All) break ;
256 }
257 RawMonitor_lock->unlock() ;
258 if (ev != NULL) ev->unpark();
259 return OS_OK ;
260 }
261
262 // Any JavaThread will enter here with state _thread_blocked
263 int JvmtiRawMonitor::raw_enter(TRAPS) {
264 TEVENT (raw_enter) ;
265 void * Contended ;
266
267 // don't enter raw monitor if thread is being externally suspended, it will
268 // surprise the suspender if a "suspended" thread can still enter monitor
269 JavaThread * jt = (JavaThread *)THREAD;
270 if (THREAD->is_Java_thread()) {
271 jt->SR_lock()->lock_without_safepoint_check();
272 while (jt->is_external_suspend()) {
273 jt->SR_lock()->unlock();
274 jt->java_suspend_self();
275 jt->SR_lock()->lock_without_safepoint_check();
276 }
277 // guarded by SR_lock to avoid racing with new external suspend requests.
278 Contended = Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) ;
279 jt->SR_lock()->unlock();
280 } else {
281 Contended = Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) ;
282 }
283
284 if (Contended == THREAD) {
285 _recursions ++ ;
286 return OM_OK ;
287 }
288
289 if (Contended == NULL) {
290 guarantee (_owner == THREAD, "invariant") ;
291 guarantee (_recursions == 0, "invariant") ;
292 return OM_OK ;
293 }
294
295 THREAD->set_current_pending_monitor(this);
296
297 if (!THREAD->is_Java_thread()) {
298 // No other non-Java threads besides VM thread would acquire
299 // a raw monitor.
300 assert(THREAD->is_VM_thread(), "must be VM thread");
301 SimpleEnter (THREAD) ;
302 } else {
303 guarantee (jt->thread_state() == _thread_blocked, "invariant") ;
304 for (;;) {
305 jt->set_suspend_equivalent();
306 // cleared by handle_special_suspend_equivalent_condition() or
307 // java_suspend_self()
308 SimpleEnter (THREAD) ;
309
310 // were we externally suspended while we were waiting?
311 if (!jt->handle_special_suspend_equivalent_condition()) break ;
312
313 // This thread was externally suspended
314 //
315 // This logic isn't needed for JVMTI raw monitors,
316 // but doesn't hurt just in case the suspend rules change. This
317 // logic is needed for the JvmtiRawMonitor.wait() reentry phase.
318 // We have reentered the contended monitor, but while we were
319 // waiting another thread suspended us. We don't want to reenter
320 // the monitor while suspended because that would surprise the
321 // thread that suspended us.
322 //
323 // Drop the lock -
324 SimpleExit (THREAD) ;
325
326 jt->java_suspend_self();
327 }
328
329 assert(_owner == THREAD, "Fatal error with monitor owner!");
330 assert(_recursions == 0, "Fatal error with monitor recursions!");
331 }
332
333 THREAD->set_current_pending_monitor(NULL);
334 guarantee (_recursions == 0, "invariant") ;
335 return OM_OK;
336 }
337
338 // Used mainly for JVMTI raw monitor implementation
339 // Also used for JvmtiRawMonitor::wait().
340 int JvmtiRawMonitor::raw_exit(TRAPS) {
341 TEVENT (raw_exit) ;
342 if (THREAD != _owner) {
343 return OM_ILLEGAL_MONITOR_STATE;
344 }
345 if (_recursions > 0) {
346 --_recursions ;
347 return OM_OK ;
348 }
349
350 void * List = _EntryList ;
351 SimpleExit (THREAD) ;
352
353 return OM_OK;
354 }
355
356 // Used for JVMTI raw monitor implementation.
357 // All JavaThreads will enter here with state _thread_blocked
358
359 int JvmtiRawMonitor::raw_wait(jlong millis, bool interruptible, TRAPS) {
360 TEVENT (raw_wait) ;
361 if (THREAD != _owner) {
362 return OM_ILLEGAL_MONITOR_STATE;
363 }
364
365 // To avoid spurious wakeups we reset the parkevent -- This is strictly optional.
366 // The caller must be able to tolerate spurious returns from raw_wait().
367 THREAD->_ParkEvent->reset() ;
368 OrderAccess::fence() ;
369
370 // check interrupt event
371 if (interruptible && Thread::is_interrupted(THREAD, true)) {
372 return OM_INTERRUPTED;
373 }
374
375 intptr_t save = _recursions ;
376 _recursions = 0 ;
377 _waiters ++ ;
378 if (THREAD->is_Java_thread()) {
379 guarantee (((JavaThread *) THREAD)->thread_state() == _thread_blocked, "invariant") ;
380 ((JavaThread *)THREAD)->set_suspend_equivalent();
381 }
382 int rv = SimpleWait (THREAD, millis) ;
383 _recursions = save ;
384 _waiters -- ;
385
386 guarantee (THREAD == _owner, "invariant") ;
387 if (THREAD->is_Java_thread()) {
388 JavaThread * jSelf = (JavaThread *) THREAD ;
389 for (;;) {
390 if (!jSelf->handle_special_suspend_equivalent_condition()) break ;
391 SimpleExit (THREAD) ;
392 jSelf->java_suspend_self();
393 SimpleEnter (THREAD) ;
394 jSelf->set_suspend_equivalent() ;
395 }
396 }
397 guarantee (THREAD == _owner, "invariant") ;
398
399 if (interruptible && Thread::is_interrupted(THREAD, true)) {
400 return OM_INTERRUPTED;
401 }
402 return OM_OK ;
403 }
404
405 int JvmtiRawMonitor::raw_notify(TRAPS) {
406 TEVENT (raw_notify) ;
407 if (THREAD != _owner) {
408 return OM_ILLEGAL_MONITOR_STATE;
409 }
410 SimpleNotify (THREAD, false) ;
411 return OM_OK;
412 }
413
414 int JvmtiRawMonitor::raw_notifyAll(TRAPS) {
415 TEVENT (raw_notifyAll) ;
416 if (THREAD != _owner) {
417 return OM_ILLEGAL_MONITOR_STATE;
418 }
419 SimpleNotify (THREAD, true) ;
420 return OM_OK;
421 }
422