1 /*
2 * Copyright (c) 2003, 2016, 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/atomic.hpp"
28 #include "runtime/interfaceSupport.hpp"
29 #include "runtime/orderAccess.inline.hpp"
30 #include "runtime/thread.inline.hpp"
31
32 GrowableArray<JvmtiRawMonitor*> *JvmtiPendingMonitors::_monitors = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<JvmtiRawMonitor*>(1,true);
33
34 void JvmtiPendingMonitors::transition_raw_monitors() {
35 assert((Threads::number_of_threads()==1),
36 "Java thread has not created yet or more than one java thread \
37 is running. Raw monitor transition will not work");
38 JavaThread *current_java_thread = JavaThread::current();
39 assert(current_java_thread->thread_state() == _thread_in_vm, "Must be in vm");
40 {
41 ThreadBlockInVM __tbivm(current_java_thread);
42 for(int i=0; i< count(); i++) {
43 JvmtiRawMonitor *rmonitor = monitors()->at(i);
44 int r = rmonitor->raw_enter(current_java_thread);
45 assert(r == ObjectMonitor::OM_OK, "raw_enter should have worked");
46 }
47 }
48 // pending monitors are converted to real monitor so delete them all.
49 dispose();
50 }
51
52 //
53 // class JvmtiRawMonitor
54 //
55
56 JvmtiRawMonitor::JvmtiRawMonitor(const char *name) {
57 #ifdef ASSERT
58 _name = strcpy(NEW_C_HEAP_ARRAY(char, strlen(name) + 1, mtInternal), name);
59 #else
60 _name = NULL;
61 #endif
62 _magic = JVMTI_RM_MAGIC;
63 }
64
65 JvmtiRawMonitor::~JvmtiRawMonitor() {
66 #ifdef ASSERT
67 FreeHeap(_name);
68 #endif
69 _magic = 0;
70 }
71
72
73 bool
74 JvmtiRawMonitor::is_valid() {
75 int value = 0;
76
77 // This object might not be a JvmtiRawMonitor so we can't assume
78 // the _magic field is properly aligned. Get the value in a safe
79 // way and then check against JVMTI_RM_MAGIC.
80
81 switch (sizeof(_magic)) {
82 case 2:
83 value = Bytes::get_native_u2((address)&_magic);
84 break;
85
86 case 4:
87 value = Bytes::get_native_u4((address)&_magic);
88 break;
89
90 case 8:
91 value = Bytes::get_native_u8((address)&_magic);
92 break;
93
94 default:
95 guarantee(false, "_magic field is an unexpected size");
96 }
97
98 return value == JVMTI_RM_MAGIC;
99 }
100
101 // -------------------------------------------------------------------------
102 // The raw monitor subsystem is entirely distinct from normal
103 // java-synchronization or jni-synchronization. raw monitors are not
104 // associated with objects. They can be implemented in any manner
105 // that makes sense. The original implementors decided to piggy-back
106 // the raw-monitor implementation on the existing Java objectMonitor mechanism.
107 // This flaw needs to fixed. We should reimplement raw monitors as sui-generis.
108 // Specifically, we should not implement raw monitors via java monitors.
109 // Time permitting, we should disentangle and deconvolve the two implementations
110 // and move the resulting raw monitor implementation over to the JVMTI directories.
111 // Ideally, the raw monitor implementation would be built on top of
112 // park-unpark and nothing else.
113 //
114 // raw monitors are used mainly by JVMTI
115 // The raw monitor implementation borrows the ObjectMonitor structure,
116 // but the operators are degenerate and extremely simple.
117 //
118 // Mixed use of a single objectMonitor instance -- as both a raw monitor
119 // and a normal java monitor -- is not permissible.
120 //
121 // Note that we use the single RawMonitor_lock to protect queue operations for
122 // _all_ raw monitors. This is a scalability impediment, but since raw monitor usage
123 // is deprecated and rare, this is not of concern. The RawMonitor_lock can not
124 // be held indefinitely. The critical sections must be short and bounded.
125 //
126 // -------------------------------------------------------------------------
127
128 int JvmtiRawMonitor::SimpleEnter (Thread * Self) {
129 for (;;) {
130 if (Atomic::cmpxchg(Self, &_owner, (void*)NULL) == NULL) {
131 return OS_OK ;
132 }
133
134 ObjectWaiter Node (Self) ;
135 Self->_ParkEvent->reset() ; // strictly optional
136 Node.TState = ObjectWaiter::TS_ENTER ;
137
138 RawMonitor_lock->lock_without_safepoint_check() ;
139 Node._next = _EntryList ;
140 _EntryList = &Node ;
141 OrderAccess::fence() ;
142 if (_owner == NULL && Atomic::cmpxchg(Self, &_owner, (void*)NULL) == NULL) {
143 _EntryList = Node._next ;
144 RawMonitor_lock->unlock() ;
145 return OS_OK ;
146 }
147 RawMonitor_lock->unlock() ;
148 while (Node.TState == ObjectWaiter::TS_ENTER) {
149 Self->_ParkEvent->park() ;
150 }
151 }
152 }
153
154 int JvmtiRawMonitor::SimpleExit (Thread * Self) {
155 guarantee (_owner == Self, "invariant") ;
156 OrderAccess::release_store(&_owner, (void*)NULL) ;
157 OrderAccess::fence() ;
158 if (_EntryList == NULL) return OS_OK ;
159 ObjectWaiter * w ;
160
161 RawMonitor_lock->lock_without_safepoint_check() ;
162 w = _EntryList ;
163 if (w != NULL) {
164 _EntryList = w->_next ;
165 }
166 RawMonitor_lock->unlock() ;
167 if (w != NULL) {
168 guarantee (w ->TState == ObjectWaiter::TS_ENTER, "invariant") ;
169 ParkEvent * ev = w->_event ;
170 w->TState = ObjectWaiter::TS_RUN ;
171 OrderAccess::fence() ;
172 ev->unpark() ;
173 }
174 return OS_OK ;
175 }
176
177 int JvmtiRawMonitor::SimpleWait (Thread * Self, jlong millis) {
178 guarantee (_owner == Self , "invariant") ;
179 guarantee (_recursions == 0, "invariant") ;
180
181 ObjectWaiter Node (Self) ;
182 Node._notified = 0 ;
183 Node.TState = ObjectWaiter::TS_WAIT ;
184
185 RawMonitor_lock->lock_without_safepoint_check() ;
186 Node._next = _WaitSet ;
187 _WaitSet = &Node ;
188 RawMonitor_lock->unlock() ;
189
190 SimpleExit (Self) ;
191 guarantee (_owner != Self, "invariant") ;
192
193 int ret = OS_OK ;
194 if (millis <= 0) {
195 Self->_ParkEvent->park();
196 } else {
197 ret = Self->_ParkEvent->park(millis);
198 }
199
200 // If thread still resides on the waitset then unlink it.
201 // Double-checked locking -- the usage is safe in this context
202 // as we TState is volatile and the lock-unlock operators are
203 // serializing (barrier-equivalent).
204
205 if (Node.TState == ObjectWaiter::TS_WAIT) {
206 RawMonitor_lock->lock_without_safepoint_check() ;
207 if (Node.TState == ObjectWaiter::TS_WAIT) {
208 // Simple O(n) unlink, but performance isn't critical here.
209 ObjectWaiter * p ;
210 ObjectWaiter * q = NULL ;
211 for (p = _WaitSet ; p != &Node; p = p->_next) {
212 q = p ;
213 }
214 guarantee (p == &Node, "invariant") ;
215 if (q == NULL) {
216 guarantee (p == _WaitSet, "invariant") ;
217 _WaitSet = p->_next ;
218 } else {
219 guarantee (p == q->_next, "invariant") ;
220 q->_next = p->_next ;
221 }
222 Node.TState = ObjectWaiter::TS_RUN ;
223 }
224 RawMonitor_lock->unlock() ;
225 }
226
227 guarantee (Node.TState == ObjectWaiter::TS_RUN, "invariant") ;
228 SimpleEnter (Self) ;
229
230 guarantee (_owner == Self, "invariant") ;
231 guarantee (_recursions == 0, "invariant") ;
232 return ret ;
233 }
234
235 int JvmtiRawMonitor::SimpleNotify (Thread * Self, bool All) {
236 guarantee (_owner == Self, "invariant") ;
237 if (_WaitSet == NULL) return OS_OK ;
238
239 // We have two options:
240 // A. Transfer the threads from the WaitSet to the EntryList
241 // B. Remove the thread from the WaitSet and unpark() it.
242 //
243 // We use (B), which is crude and results in lots of futile
244 // context switching. In particular (B) induces lots of contention.
245
246 ParkEvent * ev = NULL ; // consider using a small auto array ...
247 RawMonitor_lock->lock_without_safepoint_check() ;
248 for (;;) {
249 ObjectWaiter * w = _WaitSet ;
250 if (w == NULL) break ;
251 _WaitSet = w->_next ;
252 if (ev != NULL) { ev->unpark(); ev = NULL; }
253 ev = w->_event ;
254 OrderAccess::loadstore() ;
255 w->TState = ObjectWaiter::TS_RUN ;
256 OrderAccess::storeload();
257 if (!All) break ;
258 }
259 RawMonitor_lock->unlock() ;
260 if (ev != NULL) ev->unpark();
261 return OS_OK ;
262 }
263
264 // Any JavaThread will enter here with state _thread_blocked
265 int JvmtiRawMonitor::raw_enter(TRAPS) {
266 TEVENT (raw_enter) ;
267 void * Contended ;
268
269 // don't enter raw monitor if thread is being externally suspended, it will
270 // surprise the suspender if a "suspended" thread can still enter monitor
271 JavaThread * jt = (JavaThread *)THREAD;
272 if (THREAD->is_Java_thread()) {
273 jt->SR_lock()->lock_without_safepoint_check();
274 while (jt->is_external_suspend()) {
275 jt->SR_lock()->unlock();
276 jt->java_suspend_self();
277 jt->SR_lock()->lock_without_safepoint_check();
278 }
279 // guarded by SR_lock to avoid racing with new external suspend requests.
280 Contended = Atomic::cmpxchg(THREAD, &_owner, (void*)NULL);
281 jt->SR_lock()->unlock();
282 } else {
283 Contended = Atomic::cmpxchg(THREAD, &_owner, (void*)NULL);
284 }
285
286 if (Contended == THREAD) {
287 _recursions ++ ;
288 return OM_OK ;
289 }
290
291 if (Contended == NULL) {
292 guarantee (_owner == THREAD, "invariant") ;
293 guarantee (_recursions == 0, "invariant") ;
294 return OM_OK ;
295 }
296
297 THREAD->set_current_pending_monitor(this);
298
299 if (!THREAD->is_Java_thread()) {
300 // No other non-Java threads besides VM thread would acquire
301 // a raw monitor.
302 assert(THREAD->is_VM_thread(), "must be VM thread");
303 SimpleEnter (THREAD) ;
304 } else {
305 guarantee (jt->thread_state() == _thread_blocked, "invariant") ;
306 for (;;) {
307 jt->set_suspend_equivalent();
308 // cleared by handle_special_suspend_equivalent_condition() or
309 // java_suspend_self()
310 SimpleEnter (THREAD) ;
311
312 // were we externally suspended while we were waiting?
313 if (!jt->handle_special_suspend_equivalent_condition()) break ;
314
315 // This thread was externally suspended
316 //
317 // This logic isn't needed for JVMTI raw monitors,
318 // but doesn't hurt just in case the suspend rules change. This
319 // logic is needed for the JvmtiRawMonitor.wait() reentry phase.
320 // We have reentered the contended monitor, but while we were
321 // waiting another thread suspended us. We don't want to reenter
322 // the monitor while suspended because that would surprise the
323 // thread that suspended us.
324 //
325 // Drop the lock -
326 SimpleExit (THREAD) ;
327
328 jt->java_suspend_self();
329 }
330
331 assert(_owner == THREAD, "Fatal error with monitor owner!");
332 assert(_recursions == 0, "Fatal error with monitor recursions!");
333 }
334
335 THREAD->set_current_pending_monitor(NULL);
336 guarantee (_recursions == 0, "invariant") ;
337 return OM_OK;
338 }
339
340 // Used mainly for JVMTI raw monitor implementation
341 // Also used for JvmtiRawMonitor::wait().
342 int JvmtiRawMonitor::raw_exit(TRAPS) {
343 TEVENT (raw_exit) ;
344 if (THREAD != _owner) {
345 return OM_ILLEGAL_MONITOR_STATE;
346 }
347 if (_recursions > 0) {
348 --_recursions ;
349 return OM_OK ;
350 }
351
352 void * List = _EntryList ;
353 SimpleExit (THREAD) ;
354
355 return OM_OK;
356 }
357
358 // Used for JVMTI raw monitor implementation.
359 // All JavaThreads will enter here with state _thread_blocked
360
361 int JvmtiRawMonitor::raw_wait(jlong millis, bool interruptible, TRAPS) {
362 TEVENT (raw_wait) ;
363 if (THREAD != _owner) {
364 return OM_ILLEGAL_MONITOR_STATE;
365 }
366
367 // To avoid spurious wakeups we reset the parkevent -- This is strictly optional.
368 // The caller must be able to tolerate spurious returns from raw_wait().
369 THREAD->_ParkEvent->reset() ;
370 OrderAccess::fence() ;
371
372 // check interrupt event
373 if (interruptible && Thread::is_interrupted(THREAD, true)) {
374 return OM_INTERRUPTED;
375 }
376
377 intptr_t save = _recursions ;
378 _recursions = 0 ;
379 _waiters ++ ;
380 if (THREAD->is_Java_thread()) {
381 guarantee (((JavaThread *) THREAD)->thread_state() == _thread_blocked, "invariant") ;
382 ((JavaThread *)THREAD)->set_suspend_equivalent();
383 }
384 int rv = SimpleWait (THREAD, millis) ;
385 _recursions = save ;
386 _waiters -- ;
387
388 guarantee (THREAD == _owner, "invariant") ;
389 if (THREAD->is_Java_thread()) {
390 JavaThread * jSelf = (JavaThread *) THREAD ;
391 for (;;) {
392 if (!jSelf->handle_special_suspend_equivalent_condition()) break ;
393 SimpleExit (THREAD) ;
394 jSelf->java_suspend_self();
395 SimpleEnter (THREAD) ;
396 jSelf->set_suspend_equivalent() ;
397 }
398 }
399 guarantee (THREAD == _owner, "invariant") ;
400
401 if (interruptible && Thread::is_interrupted(THREAD, true)) {
402 return OM_INTERRUPTED;
403 }
404 return OM_OK ;
405 }
406
407 int JvmtiRawMonitor::raw_notify(TRAPS) {
408 TEVENT (raw_notify) ;
409 if (THREAD != _owner) {
410 return OM_ILLEGAL_MONITOR_STATE;
411 }
412 SimpleNotify (THREAD, false) ;
413 return OM_OK;
414 }
415
416 int JvmtiRawMonitor::raw_notifyAll(TRAPS) {
417 TEVENT (raw_notifyAll) ;
418 if (THREAD != _owner) {
419 return OM_ILLEGAL_MONITOR_STATE;
420 }
421 SimpleNotify (THREAD, true) ;
422 return OM_OK;
423 }
424