2 * monitor.c: Monitor locking functions
5 * Dick Porter (dick@ximian.com)
7 * (C) 2003 Ximian, Inc.
13 #include <mono/metadata/monitor.h>
14 #include <mono/metadata/threads-types.h>
15 #include <mono/metadata/exception.h>
16 #include <mono/metadata/threads.h>
17 #include <mono/io-layer/io-layer.h>
19 #include <mono/os/gc_wrapper.h>
21 #undef THREAD_LOCK_DEBUG
24 * The monitor implementation here is based on
25 * http://www.usenix.org/events/jvm01/full_papers/dice/dice.pdf and
26 * http://www.research.ibm.com/people/d/dfb/papers/Bacon98Thin.ps
28 * The Dice paper describes a technique for saving lock record space
29 * by returning records to a free list when they become unused. That
30 * sounds like unnecessary complexity to me, though if it becomes
31 * clear that unused lock records are taking up lots of space or we
32 * need to shave more time off by avoiding a malloc then we can always
33 * implement the free list idea later. The timeout parameter to
34 * try_enter voids some of the assumptions about the reference count
35 * field in Dice's implementation too. In his version, the thread
36 * attempting to lock a contended object will block until it succeeds,
37 * so the reference count will never be decremented while an object is
40 * Bacon's thin locks have a fast path that doesn't need a lock record
41 * for the common case of locking an unlocked or shallow-nested
42 * object, but the technique relies on encoding the thread ID in 15
43 * bits (to avoid too much per-object space overhead.) Unfortunately
44 * I don't think it's possible to reliably encode a pthread_t into 15
45 * bits. (The JVM implementation used seems to have a 15-bit
46 * per-thread identifier available.)
48 * This implementation then combines Dice's basic lock model with
49 * Bacon's simplification of keeping a lock record for the lifetime of
54 static void mon_finalize (void *o, void *unused)
56 MonoThreadsSync *mon=(MonoThreadsSync *)o;
58 #ifdef THREAD_LOCK_DEBUG
59 g_message (G_GNUC_PRETTY_FUNCTION ": Finalizing sync %p", mon);
62 if(mon->entry_sem!=NULL) {
63 CloseHandle (mon->entry_sem);
65 /* If this isn't empty then something is seriously broken - it
66 * means a thread is still waiting on the object that owned
67 * this lock, but the object has been finalized.
69 g_assert (mon->wait_list==NULL);
72 static MonoThreadsSync *mon_new(guint32 id)
77 new=(MonoThreadsSync *)GC_MALLOC (sizeof(MonoThreadsSync));
78 GC_REGISTER_FINALIZER (new, mon_finalize, NULL, NULL, NULL);
80 /* This should be freed when the object that owns it is
83 new=(MonoThreadsSync *)g_new0 (MonoThreadsSync, 1);
91 /* If allow_interruption==TRUE, the method will be interrumped if abort or suspend
92 * is requested. In this case it returns -1.
94 static gint32 mono_monitor_try_enter_internal (MonoObject *obj, guint32 ms, gboolean allow_interruption)
97 guint32 id=GetCurrentThreadId ();
99 guint32 then=0, now, delta;
103 #ifdef THREAD_LOCK_DEBUG
104 g_message(G_GNUC_PRETTY_FUNCTION
105 ": (%d) Trying to lock object %p (%d ms)", id, obj, ms);
109 mon=obj->synchronisation;
111 /* If the object has never been locked... */
114 if(InterlockedCompareExchangePointer ((gpointer*)&obj->synchronisation, mon, NULL)==NULL) {
115 /* Successfully locked */
118 /* Another thread got in first, so try again.
119 * GC will take care of the monitor record
121 #ifndef HAVE_BOEHM_GC
122 mon_finalize (mon, NULL);
128 /* If the object is currently locked by this thread... */
134 /* If the object has previously been locked but isn't now... */
136 /* This case differs from Dice's case 3 because we don't
137 * deflate locks or cache unused lock records
140 /* Try to install our ID in the owner field, nest
141 * should have been left at 1 by the previous unlock
144 if(InterlockedCompareExchange (&mon->owner, id, 0)==0) {
146 g_assert (mon->nest==1);
154 /* The object must be locked by someone else... */
156 /* If ms is 0 we don't block, but just fail straight away */
158 #ifdef THREAD_LOCK_DEBUG
159 g_message (G_GNUC_PRETTY_FUNCTION
160 ": (%d) timed out, returning FALSE", id);
166 /* The slow path begins here. We need to make sure theres a
167 * semaphore handle (creating it if necessary), and block on
170 if(mon->entry_sem==NULL) {
171 /* Create the semaphore */
172 sem=CreateSemaphore (NULL, 0, 0x7fffffff, NULL);
173 if(InterlockedCompareExchangePointer ((gpointer*)&mon->entry_sem, sem, NULL)!=NULL) {
174 /* Someone else just put a handle here */
179 /* If we need to time out, record a timestamp and adjust ms,
180 * because WaitForSingleObject doesn't tell us how long it
183 * Don't block forever here, because theres a chance the owner
184 * thread released the lock while we were creating the
185 * semaphore: we would not get the wakeup. Using the event
186 * handle technique from pulse/wait would involve locking the
187 * lock struct and therefore slowing down the fast path.
190 then=GetTickCount ();
200 InterlockedIncrement (&mon->entry_count);
201 ret=WaitForSingleObjectEx (mon->entry_sem, waitms, allow_interruption);
202 InterlockedDecrement (&mon->entry_count);
208 /* The counter must have wrapped around */
209 #ifdef THREAD_LOCK_DEBUG
210 g_message (G_GNUC_PRETTY_FUNCTION
211 ": wrapped around! now=0x%x then=0x%x",
215 now+=(0xffffffff - then);
218 #ifdef THREAD_LOCK_DEBUG
219 g_message (G_GNUC_PRETTY_FUNCTION ": wrap rejig: now=0x%x then=0x%x delta=0x%x", now, then, now-then);
230 if((ret==WAIT_TIMEOUT || (ret==WAIT_IO_COMPLETION && !allow_interruption)) && ms>0) {
235 if(ret==WAIT_TIMEOUT || (ret==WAIT_IO_COMPLETION && !allow_interruption)) {
236 /* Infinite wait, so just try again */
241 if(ret==WAIT_OBJECT_0) {
242 /* retry from the top */
246 /* We must have timed out */
247 #ifdef THREAD_LOCK_DEBUG
248 g_message (G_GNUC_PRETTY_FUNCTION
249 ": (%d) timed out waiting, returning FALSE", id);
252 if (ret==WAIT_IO_COMPLETION) return(-1);
256 gboolean mono_monitor_enter (MonoObject *obj)
258 return mono_monitor_try_enter_internal (obj, INFINITE, FALSE) == 1;
261 gboolean mono_monitor_try_enter (MonoObject *obj, guint32 ms)
263 return mono_monitor_try_enter_internal (obj, ms, FALSE) == 1;
266 void mono_monitor_exit (MonoObject *obj)
268 MonoThreadsSync *mon;
271 #ifdef THREAD_LOCK_DEBUG
272 g_message(G_GNUC_PRETTY_FUNCTION ": (%d) Unlocking %p",
273 GetCurrentThreadId (), obj);
276 mon=obj->synchronisation;
279 mono_raise_exception (mono_get_exception_synchronization_lock ("Not locked"));
282 if(mon->owner!=GetCurrentThreadId ()) {
288 #ifdef THREAD_LOCK_DEBUG
289 g_message(G_GNUC_PRETTY_FUNCTION
290 ": (%d) Object %p is now unlocked",
291 GetCurrentThreadId (), obj);
294 /* object is now unlocked, leave nest==1 so we don't
295 * need to set it when the lock is reacquired
299 /* Do the wakeup stuff. It's possible that the last
300 * blocking thread gave up waiting just before we
301 * release the semaphore resulting in a futile wakeup
302 * next time there's contention for this object, but
303 * it means we don't have to waste time locking the
306 if(mon->entry_count>0) {
307 ReleaseSemaphore (mon->entry_sem, 1, NULL);
310 #ifdef THREAD_LOCK_DEBUG
311 g_message(G_GNUC_PRETTY_FUNCTION
312 ": (%d) Object %p is now locked %d times",
313 GetCurrentThreadId (), obj,
320 gboolean ves_icall_System_Threading_Monitor_Monitor_try_enter(MonoObject *obj,
327 res = mono_monitor_try_enter_internal (obj, ms, TRUE);
329 mono_thread_interruption_checkpoint ();
336 void ves_icall_System_Threading_Monitor_Monitor_exit(MonoObject *obj)
340 mono_monitor_exit (obj);
343 gboolean ves_icall_System_Threading_Monitor_Monitor_test_owner(MonoObject *obj)
345 MonoThreadsSync *mon;
349 #ifdef THREAD_LOCK_DEBUG
350 g_message(G_GNUC_PRETTY_FUNCTION
351 ": Testing if %p is owned by thread %d", obj,
352 GetCurrentThreadId());
355 mon=obj->synchronisation;
360 if(mon->owner==GetCurrentThreadId ()) {
367 gboolean ves_icall_System_Threading_Monitor_Monitor_test_synchronised(MonoObject *obj)
369 MonoThreadsSync *mon;
373 #ifdef THREAD_LOCK_DEBUG
374 g_message(G_GNUC_PRETTY_FUNCTION
375 ": (%d) Testing if %p is owned by any thread",
376 GetCurrentThreadId (), obj);
379 mon=obj->synchronisation;
391 /* All wait list manipulation in the pulse, pulseall and wait
392 * functions happens while the monitor lock is held, so we don't need
393 * any extra struct locking
396 void ves_icall_System_Threading_Monitor_Monitor_pulse(MonoObject *obj)
398 MonoThreadsSync *mon;
402 #ifdef THREAD_LOCK_DEBUG
403 g_message(G_GNUC_PRETTY_FUNCTION ": (%d) Pulsing %p",
404 GetCurrentThreadId (), obj);
407 mon=obj->synchronisation;
409 mono_raise_exception (mono_get_exception_synchronization_lock ("Not locked"));
412 if(mon->owner!=GetCurrentThreadId ()) {
413 mono_raise_exception (mono_get_exception_synchronization_lock ("Not locked by this thread"));
417 #ifdef THREAD_LOCK_DEBUG
418 g_message(G_GNUC_PRETTY_FUNCTION ": (%d) %d threads waiting",
419 GetCurrentThreadId (), g_slist_length (mon->wait_list));
422 if(mon->wait_list!=NULL) {
423 #ifdef THREAD_LOCK_DEBUG
424 g_message(G_GNUC_PRETTY_FUNCTION
425 ": (%d) signalling and dequeuing handle %p",
426 GetCurrentThreadId (), mon->wait_list->data);
429 SetEvent (mon->wait_list->data);
430 mon->wait_list=g_slist_remove (mon->wait_list,
431 mon->wait_list->data);
435 void ves_icall_System_Threading_Monitor_Monitor_pulse_all(MonoObject *obj)
437 MonoThreadsSync *mon;
441 #ifdef THREAD_LOCK_DEBUG
442 g_message(G_GNUC_PRETTY_FUNCTION ": (%d) Pulsing all %p",
443 GetCurrentThreadId (), obj);
446 mon=obj->synchronisation;
448 mono_raise_exception (mono_get_exception_synchronization_lock ("Not locked"));
451 if(mon->owner!=GetCurrentThreadId ()) {
452 mono_raise_exception (mono_get_exception_synchronization_lock ("Not locked by this thread"));
456 #ifdef THREAD_LOCK_DEBUG
457 g_message(G_GNUC_PRETTY_FUNCTION ": (%d) %d threads waiting",
458 GetCurrentThreadId (), g_slist_length (mon->wait_list));
461 while(mon->wait_list!=NULL) {
462 #ifdef THREAD_LOCK_DEBUG
463 g_message(G_GNUC_PRETTY_FUNCTION
464 ": (%d) signalling and dequeuing handle %p",
465 GetCurrentThreadId (), mon->wait_list->data);
468 SetEvent (mon->wait_list->data);
469 mon->wait_list=g_slist_remove (mon->wait_list,
470 mon->wait_list->data);
474 gboolean ves_icall_System_Threading_Monitor_Monitor_wait(MonoObject *obj,
477 MonoThreadsSync *mon;
481 gboolean success=FALSE;
486 #ifdef THREAD_LOCK_DEBUG
487 g_message(G_GNUC_PRETTY_FUNCTION
488 ": (%d) Trying to wait for %p with timeout %dms",
489 GetCurrentThreadId (), obj, ms);
492 mon=obj->synchronisation;
494 mono_raise_exception (mono_get_exception_synchronization_lock ("Not locked"));
497 if(mon->owner!=GetCurrentThreadId ()) {
498 mono_raise_exception (mono_get_exception_synchronization_lock ("Not locked by this thread"));
502 event=CreateEvent (NULL, FALSE, FALSE, NULL);
504 mono_raise_exception (mono_get_exception_synchronization_lock ("Failed to set up wait event"));
508 #ifdef THREAD_LOCK_DEBUG
509 g_message(G_GNUC_PRETTY_FUNCTION ": (%d) queuing handle %p",
510 GetCurrentThreadId (), event);
513 mon->wait_list=g_slist_append (mon->wait_list, event);
515 /* Save the nest count, and release the lock */
518 mono_monitor_exit (obj);
520 #ifdef THREAD_LOCK_DEBUG
521 g_message(G_GNUC_PRETTY_FUNCTION ": (%d) Unlocked %p lock %p",
522 GetCurrentThreadId (), obj, mon);
525 /* There's no race between unlocking mon and waiting for the
526 * event, because auto reset events are sticky, and this event
527 * is private to this thread. Therefore even if the event was
528 * signalled before we wait, we still succeed.
530 ret=WaitForSingleObjectEx (event, ms, TRUE);
532 if (mono_thread_interruption_requested ()) {
537 /* Regain the lock with the previous nest count */
539 regain=mono_monitor_try_enter_internal (obj, INFINITE, TRUE);
541 mono_thread_interruption_checkpoint ();
543 while (regain == -1);
546 /* Something went wrong, so throw a
547 * SynchronizationLockException
550 mono_raise_exception (mono_get_exception_synchronization_lock ("Failed to regain lock"));
556 #ifdef THREAD_LOCK_DEBUG
557 g_message(G_GNUC_PRETTY_FUNCTION ": (%d) Regained %p lock %p",
558 GetCurrentThreadId (), obj, mon);
561 if(ret==WAIT_TIMEOUT) {
562 /* Poll the event again, just in case it was signalled
563 * while we were trying to regain the monitor lock
565 ret=WaitForSingleObjectEx (event, 0, FALSE);
568 /* Pulse will have popped our event from the queue if it signalled
569 * us, so we only do it here if the wait timed out.
571 * This avoids a race condition where the thread holding the
572 * lock can Pulse several times before the WaitForSingleObject
573 * returns. If we popped the queue here then this event might
574 * be signalled more than once, thereby starving another
578 if(ret==WAIT_OBJECT_0) {
579 #ifdef THREAD_LOCK_DEBUG
580 g_message(G_GNUC_PRETTY_FUNCTION ": (%d) Success",
581 GetCurrentThreadId ());
585 #ifdef THREAD_LOCK_DEBUG
586 g_message(G_GNUC_PRETTY_FUNCTION ": (%d) Wait failed",
587 GetCurrentThreadId ());
588 g_message(G_GNUC_PRETTY_FUNCTION ": (%d) dequeuing handle %p",
589 GetCurrentThreadId (), event);
591 /* No pulse, so we have to remove ourself from the
594 mon->wait_list=g_slist_remove (mon->wait_list, event);