6 * Rodrigo Kumpera (kumpera@gmail.com)
8 * Copyright 2011 Novell, Inc (http://www.novell.com)
9 * Copyright 2011 Xamarin, Inc (http://www.xamarin.com)
10 * Licensed under the MIT license. See LICENSE file in the project root for full license information.
15 /* enable pthread extensions */
17 #define _DARWIN_C_SOURCE
20 #include <mono/utils/mono-compiler.h>
21 #include <mono/utils/mono-os-semaphore.h>
22 #include <mono/utils/mono-threads.h>
23 #include <mono/utils/mono-tls.h>
24 #include <mono/utils/hazard-pointer.h>
25 #include <mono/utils/mono-memory-model.h>
26 #include <mono/utils/mono-mmap.h>
27 #include <mono/utils/atomic.h>
28 #include <mono/utils/mono-time.h>
29 #include <mono/utils/mono-lazy-init.h>
30 #include <mono/utils/mono-coop-mutex.h>
31 #include <mono/utils/mono-coop-semaphore.h>
32 #include <mono/utils/mono-threads-coop.h>
33 #include <mono/utils/mono-threads-debug.h>
34 #include <mono/utils/os-event.h>
35 #include <mono/utils/w32api.h>
40 #include <mono/utils/mach-support.h>
44 Mutex that makes sure only a single thread can be suspending others.
45 Suspend is a very racy operation since it requires restarting until
46 the target thread is not on an unsafe region.
48 We could implement this using critical regions, but would be much much
49 harder for an operation that is hardly performance critical.
51 The GC has to acquire this lock before starting a STW to make sure
52 a runtime suspend won't make it wronly see a thread in a safepoint
53 when it is in fact not.
55 This has to be a naked locking primitive, and not a coop aware one, as
56 it needs to be usable when destroying thread_info_key, the TLS key for
57 the current MonoThreadInfo. In this case, mono_thread_info_current_unchecked,
58 (which is used inside MONO_ENTER_GC_SAFE), would return NULL, leading
59 to an assertion error. We then simply switch state manually in
60 mono_thread_info_suspend_lock_with_info.
62 static MonoSemType global_suspend_semaphore;
64 static size_t thread_info_size;
65 static MonoThreadInfoCallbacks threads_callbacks;
66 static MonoThreadInfoRuntimeCallbacks runtime_callbacks;
67 static MonoNativeTlsKey thread_info_key, thread_exited_key;
69 static __thread guint32 tls_small_id;
71 static MonoNativeTlsKey small_id_key;
73 static MonoLinkedListSet thread_list;
74 static gboolean mono_threads_inited = FALSE;
76 static MonoSemType suspend_semaphore;
77 static size_t pending_suspends;
79 static mono_mutex_t join_mutex;
81 #define mono_thread_info_run_state(info) (((MonoThreadInfo*)info)->thread_state & THREAD_STATE_MASK)
84 #define SLEEP_DURATION_BEFORE_WARNING (50)
86 #define SLEEP_DURATION_BEFORE_ABORT MONO_INFINITE_WAIT
88 static guint32 sleepWarnDuration = SLEEP_DURATION_BEFORE_WARNING,
89 sleepAbortDuration = SLEEP_DURATION_BEFORE_ABORT;
91 static int suspend_posts, resume_posts, abort_posts, waits_done, pending_ops;
94 mono_threads_notify_initiator_of_abort (MonoThreadInfo* info)
96 THREADS_SUSPEND_DEBUG ("[INITIATOR-NOTIFY-ABORT] %p\n", mono_thread_info_get_tid (info));
97 InterlockedIncrement (&abort_posts);
98 mono_os_sem_post (&suspend_semaphore);
102 mono_threads_notify_initiator_of_suspend (MonoThreadInfo* info)
104 THREADS_SUSPEND_DEBUG ("[INITIATOR-NOTIFY-SUSPEND] %p\n", mono_thread_info_get_tid (info));
105 InterlockedIncrement (&suspend_posts);
106 mono_os_sem_post (&suspend_semaphore);
110 mono_threads_notify_initiator_of_resume (MonoThreadInfo* info)
112 THREADS_SUSPEND_DEBUG ("[INITIATOR-NOTIFY-RESUME] %p\n", mono_thread_info_get_tid (info));
113 InterlockedIncrement (&resume_posts);
114 mono_os_sem_post (&suspend_semaphore);
118 begin_async_suspend (MonoThreadInfo *info, gboolean interrupt_kernel)
120 if (mono_threads_is_coop_enabled ()) {
121 /* There's nothing else to do after we async request the thread to suspend */
122 mono_threads_add_to_pending_operation_set (info);
126 return mono_threads_suspend_begin_async_suspend (info, interrupt_kernel);
130 check_async_suspend (MonoThreadInfo *info)
132 if (mono_threads_is_coop_enabled ()) {
133 /* Async suspend can't async fail on coop */
137 return mono_threads_suspend_check_suspend_result (info);
141 resume_async_suspended (MonoThreadInfo *info)
143 if (mono_threads_is_coop_enabled ())
144 g_assert_not_reached ();
146 g_assert (mono_threads_suspend_begin_async_resume (info));
150 resume_self_suspended (MonoThreadInfo* info)
152 THREADS_SUSPEND_DEBUG ("**BEGIN self-resume %p\n", mono_thread_info_get_tid (info));
153 mono_os_sem_post (&info->resume_semaphore);
157 mono_thread_info_wait_for_resume (MonoThreadInfo* info)
160 THREADS_SUSPEND_DEBUG ("**WAIT self-resume %p\n", mono_thread_info_get_tid (info));
161 res = mono_os_sem_wait (&info->resume_semaphore, MONO_SEM_FLAGS_NONE);
162 g_assert (res != -1);
166 resume_blocking_suspended (MonoThreadInfo* info)
168 THREADS_SUSPEND_DEBUG ("**BEGIN blocking-resume %p\n", mono_thread_info_get_tid (info));
169 mono_os_sem_post (&info->resume_semaphore);
173 mono_threads_add_to_pending_operation_set (MonoThreadInfo* info)
175 THREADS_SUSPEND_DEBUG ("added %p to pending suspend\n", mono_thread_info_get_tid (info));
177 InterlockedIncrement (&pending_ops);
181 mono_threads_begin_global_suspend (void)
183 size_t ps = pending_suspends;
184 if (G_UNLIKELY (ps != 0))
185 g_error ("pending_suspends = %d, but must be 0", ps);
186 THREADS_SUSPEND_DEBUG ("------ BEGIN GLOBAL OP sp %d rp %d ap %d wd %d po %d (sp + rp + ap == wd) (wd == po)\n", suspend_posts, resume_posts,
187 abort_posts, waits_done, pending_ops);
188 g_assert ((suspend_posts + resume_posts + abort_posts) == waits_done);
189 mono_threads_coop_begin_global_suspend ();
193 mono_threads_end_global_suspend (void)
195 size_t ps = pending_suspends;
196 if (G_UNLIKELY (ps != 0))
197 g_error ("pending_suspends = %d, but must be 0", ps);
198 THREADS_SUSPEND_DEBUG ("------ END GLOBAL OP sp %d rp %d ap %d wd %d po %d\n", suspend_posts, resume_posts,
199 abort_posts, waits_done, pending_ops);
200 g_assert ((suspend_posts + resume_posts + abort_posts) == waits_done);
201 mono_threads_coop_end_global_suspend ();
207 MonoThreadInfo *cur = mono_thread_info_current ();
209 MOSTLY_ASYNC_SAFE_PRINTF ("STATE CUE CARD: (? means a positive number, usually 1 or 2, * means any number)\n");
210 MOSTLY_ASYNC_SAFE_PRINTF ("\t0x0\t- starting (GOOD, unless the thread is running managed code)\n");
211 MOSTLY_ASYNC_SAFE_PRINTF ("\t0x1\t- running (BAD, unless it's the gc thread)\n");
212 MOSTLY_ASYNC_SAFE_PRINTF ("\t0x2\t- detached (GOOD, unless the thread is running managed code)\n");
213 MOSTLY_ASYNC_SAFE_PRINTF ("\t0x?03\t- async suspended (GOOD)\n");
214 MOSTLY_ASYNC_SAFE_PRINTF ("\t0x?04\t- self suspended (GOOD)\n");
215 MOSTLY_ASYNC_SAFE_PRINTF ("\t0x?05\t- async suspend requested (BAD)\n");
216 MOSTLY_ASYNC_SAFE_PRINTF ("\t0x?06\t- self suspend requested (BAD)\n");
217 MOSTLY_ASYNC_SAFE_PRINTF ("\t0x*07\t- blocking (GOOD)\n");
218 MOSTLY_ASYNC_SAFE_PRINTF ("\t0x?08\t- blocking with pending suspend (GOOD)\n");
220 FOREACH_THREAD_SAFE (info) {
222 char thread_name [256] = { 0 };
223 pthread_getname_np (mono_thread_info_get_tid (info), thread_name, 255);
225 MOSTLY_ASYNC_SAFE_PRINTF ("--thread %p id %p [%p] (%s) state %x %s\n", info, (void *) mono_thread_info_get_tid (info), (void*)(size_t)info->native_handle, thread_name, info->thread_state, info == cur ? "GC INITIATOR" : "" );
227 MOSTLY_ASYNC_SAFE_PRINTF ("--thread %p id %p [%p] state %x %s\n", info, (void *) mono_thread_info_get_tid (info), (void*)(size_t)info->native_handle, info->thread_state, info == cur ? "GC INITIATOR" : "" );
229 } FOREACH_THREAD_SAFE_END
233 mono_threads_wait_pending_operations (void)
236 int c = pending_suspends;
238 /* Wait threads to park */
239 THREADS_SUSPEND_DEBUG ("[INITIATOR-WAIT-COUNT] %d\n", c);
240 if (pending_suspends) {
241 MonoStopwatch suspension_time;
242 mono_stopwatch_start (&suspension_time);
243 for (i = 0; i < pending_suspends; ++i) {
244 THREADS_SUSPEND_DEBUG ("[INITIATOR-WAIT-WAITING]\n");
245 InterlockedIncrement (&waits_done);
246 if (mono_os_sem_timedwait (&suspend_semaphore, sleepAbortDuration, MONO_SEM_FLAGS_NONE) == MONO_SEM_TIMEDWAIT_RET_SUCCESS)
248 mono_stopwatch_stop (&suspension_time);
252 MOSTLY_ASYNC_SAFE_PRINTF ("WAITING for %d threads, got %d suspended\n", (int)pending_suspends, i);
253 g_error ("suspend_thread suspend took %d ms, which is more than the allowed %d ms", (int)mono_stopwatch_elapsed_ms (&suspension_time), sleepAbortDuration);
255 mono_stopwatch_stop (&suspension_time);
256 THREADS_SUSPEND_DEBUG ("Suspending %d threads took %d ms.\n", (int)pending_suspends, (int)mono_stopwatch_elapsed_ms (&suspension_time));
260 pending_suspends = 0;
266 //Thread initialization code
269 mono_hazard_pointer_clear_all (MonoThreadHazardPointers *hp, int retain)
272 mono_hazard_pointer_clear (hp, 0);
274 mono_hazard_pointer_clear (hp, 1);
276 mono_hazard_pointer_clear (hp, 2);
280 If return non null Hazard Pointer 1 holds the return value.
283 mono_thread_info_lookup (MonoNativeThreadId id)
285 MonoThreadHazardPointers *hp = mono_hazard_pointer_get ();
287 if (!mono_lls_find (&thread_list, hp, (uintptr_t)id)) {
288 mono_hazard_pointer_clear_all (hp, -1);
292 mono_hazard_pointer_clear_all (hp, 1);
293 return (MonoThreadInfo *) mono_hazard_pointer_get_val (hp, 1);
297 mono_thread_info_insert (MonoThreadInfo *info)
299 MonoThreadHazardPointers *hp = mono_hazard_pointer_get ();
301 if (!mono_lls_insert (&thread_list, hp, (MonoLinkedListSetNode*)info)) {
302 mono_hazard_pointer_clear_all (hp, -1);
306 mono_hazard_pointer_clear_all (hp, -1);
311 mono_thread_info_remove (MonoThreadInfo *info)
313 MonoThreadHazardPointers *hp = mono_hazard_pointer_get ();
316 THREADS_DEBUG ("removing info %p\n", info);
317 res = mono_lls_remove (&thread_list, hp, (MonoLinkedListSetNode*)info);
318 mono_hazard_pointer_clear_all (hp, -1);
323 free_thread_info (gpointer mem)
325 MonoThreadInfo *info = (MonoThreadInfo *) mem;
327 mono_os_sem_destroy (&info->resume_semaphore);
328 mono_threads_suspend_free (info);
334 mono_thread_info_register_small_id (void)
336 int small_id = mono_thread_small_id_alloc ();
337 #ifdef HAVE_KW_THREAD
338 tls_small_id = small_id;
340 mono_native_tls_set_value (small_id_key, GUINT_TO_POINTER (small_id + 1));
346 thread_handle_destroy (gpointer data)
348 MonoThreadHandle *thread_handle;
350 thread_handle = (MonoThreadHandle*) data;
352 mono_os_event_destroy (&thread_handle->event);
353 g_free (thread_handle);
357 register_thread (MonoThreadInfo *info, gpointer baseptr)
360 guint8 *staddr = NULL;
361 int small_id = mono_thread_info_register_small_id ();
363 mono_thread_info_set_tid (info, mono_native_thread_id_get ());
364 info->small_id = small_id;
366 info->handle = g_new0 (MonoThreadHandle, 1);
367 mono_refcount_init (info->handle, thread_handle_destroy);
368 mono_os_event_init (&info->handle->event, FALSE);
370 mono_os_sem_init (&info->resume_semaphore, 0);
372 /*set TLS early so SMR works */
373 mono_native_tls_set_value (thread_info_key, info);
375 THREADS_DEBUG ("registering info %p tid %p small id %x\n", info, mono_thread_info_get_tid (info), info->small_id);
377 if (threads_callbacks.thread_register) {
378 if (threads_callbacks.thread_register (info, baseptr) == NULL) {
379 // g_warning ("thread registation failed\n");
380 mono_native_tls_set_value (thread_info_key, NULL);
386 mono_thread_info_get_stack_bounds (&staddr, &stsize);
389 info->stack_start_limit = staddr;
390 info->stack_end = staddr + stsize;
392 info->stackdata = g_byte_array_new ();
394 mono_threads_suspend_register (info);
397 Transition it before taking any locks or publishing itself to reduce the chance
398 of others witnessing a detached thread.
399 We can reasonably expect that until this thread gets published, no other thread will
400 try to manipulate it.
402 mono_threads_transition_attach (info);
403 mono_thread_info_suspend_lock ();
404 /*If this fail it means a given thread has been registered twice, which doesn't make sense. */
405 result = mono_thread_info_insert (info);
407 mono_thread_info_suspend_unlock ();
412 mono_thread_info_suspend_lock_with_info (MonoThreadInfo *info);
415 mono_threads_signal_thread_handle (MonoThreadHandle* thread_handle);
418 unregister_thread (void *arg)
420 gpointer gc_unsafe_stackdata;
421 MonoThreadInfo *info;
426 info = (MonoThreadInfo *) arg;
428 g_assert (mono_thread_info_is_current (info));
429 g_assert (mono_thread_info_is_live (info));
431 /* Pump the HP queue while the thread is alive.*/
432 mono_thread_hazardous_try_free_some ();
434 small_id = info->small_id;
436 /* We only enter the GC unsafe region, as when exiting this function, the thread
437 * will be detached, and the current MonoThreadInfo* will be destroyed. */
438 mono_threads_enter_gc_unsafe_region_unbalanced_with_info (info, &gc_unsafe_stackdata);
440 THREADS_DEBUG ("unregistering info %p\n", info);
442 mono_native_tls_set_value (thread_exited_key, GUINT_TO_POINTER (1));
445 * TLS destruction order is not reliable so small_id might be cleaned up
448 #ifndef HAVE_KW_THREAD
449 mono_native_tls_set_value (small_id_key, GUINT_TO_POINTER (info->small_id + 1));
452 /* we need to duplicate it, as the info->handle is going
453 * to be closed when unregistering from the platform */
454 handle = mono_threads_open_thread_handle (info->handle);
457 First perform the callback that requires no locks.
458 This callback has the potential of taking other locks, so we do it before.
459 After it completes, the thread remains functional.
461 if (threads_callbacks.thread_detach)
462 threads_callbacks.thread_detach (info);
464 mono_thread_info_suspend_lock_with_info (info);
467 Now perform the callback that must be done under locks.
468 This will render the thread useless and non-suspendable, so it must
469 be done while holding the suspend lock to give no other thread chance
472 if (threads_callbacks.thread_unregister)
473 threads_callbacks.thread_unregister (info);
475 /* The thread is no longer active, so unref its handle */
476 mono_threads_close_thread_handle (info->handle);
479 result = mono_thread_info_remove (info);
481 mono_threads_transition_detach (info);
483 mono_thread_info_suspend_unlock ();
485 g_byte_array_free (info->stackdata, /*free_segment=*/TRUE);
487 /*now it's safe to free the thread info.*/
488 mono_thread_hazardous_try_free (info, free_thread_info);
490 mono_thread_small_id_free (small_id);
492 mono_threads_signal_thread_handle (handle);
494 mono_threads_close_thread_handle (handle);
498 thread_exited_dtor (void *arg)
500 #if defined(__MACH__)
502 * Since we use pthread dtors to clean up thread data, if a thread
503 * is attached to the runtime by another pthread dtor after our dtor
504 * has ran, it will never be detached, leading to various problems
505 * since the thread ids etc. will be reused while they are still in
506 * the threads hashtables etc.
507 * Dtors are called in a loop until all user tls entries are 0,
508 * but the loop has a maximum count (4), so if we set the tls
509 * variable every time, it will remain set when system tls dtors
510 * are ran. This allows mono_thread_info_is_exiting () to detect
511 * whenever the thread is exiting, even if it is executed from a
512 * system tls dtor (i.e. obj-c dealloc methods).
514 mono_native_tls_set_value (thread_exited_key, GUINT_TO_POINTER (1));
519 mono_thread_info_current_unchecked (void)
521 return mono_threads_inited ? (MonoThreadInfo*)mono_native_tls_get_value (thread_info_key) : NULL;
526 mono_thread_info_current (void)
528 MonoThreadInfo *info = (MonoThreadInfo*)mono_native_tls_get_value (thread_info_key);
532 info = mono_thread_info_lookup (mono_native_thread_id_get ()); /*info on HP1*/
535 We might be called during thread cleanup, but we cannot be called after cleanup as happened.
536 The way to distinguish between before, during and after cleanup is the following:
538 -If the TLS key is set, cleanup has not begun;
539 -If the TLS key is clean, but the thread remains registered, cleanup is in progress;
540 -If the thread is nowhere to be found, cleanup has finished.
542 We cannot function after cleanup since there's no way to ensure what will happen.
546 /*We're looking up the current thread which will not be freed until we finish running, so no need to keep it on a HP */
547 mono_hazard_pointer_clear (mono_hazard_pointer_get (), 1);
553 mono_thread_info_get_small_id (void)
555 #ifdef HAVE_KW_THREAD
558 gpointer val = mono_native_tls_get_value (small_id_key);
561 return GPOINTER_TO_INT (val) - 1;
566 mono_thread_info_list_head (void)
572 * mono_threads_attach_tools_thread
574 * Attach the current thread as a tool thread. DON'T USE THIS FUNCTION WITHOUT READING ALL DISCLAIMERS.
576 * A tools thread is a very special kind of thread that needs access to core runtime facilities but should
577 * not be counted as a regular thread for high order facilities such as executing managed code or accessing
580 * This is intended only to tools such as a profiler than needs to be able to use our lock-free support when
581 * doing things like resolving backtraces in their background processing thread.
584 mono_threads_attach_tools_thread (void)
587 MonoThreadInfo *info;
589 /* Must only be called once */
590 g_assert (!mono_native_tls_get_value (thread_info_key));
592 while (!mono_threads_inited) {
593 mono_thread_info_usleep (10);
596 info = mono_thread_info_attach (&dummy);
599 info->tools_thread = TRUE;
603 mono_thread_info_attach (void *baseptr)
605 MonoThreadInfo *info;
606 if (!mono_threads_inited)
609 /* This can happen from DllMain(DLL_THREAD_ATTACH) on Windows, if a
610 * thread is created before an embedding API user initialized Mono. */
611 THREADS_DEBUG ("mono_thread_info_attach called before mono_threads_init\n");
614 g_assert (mono_threads_inited);
617 info = (MonoThreadInfo *) mono_native_tls_get_value (thread_info_key);
619 info = (MonoThreadInfo *) g_malloc0 (thread_info_size);
620 THREADS_DEBUG ("attaching %p\n", info);
621 if (!register_thread (info, baseptr))
623 } else if (threads_callbacks.thread_attach) {
624 threads_callbacks.thread_attach (info);
630 mono_thread_info_detach (void)
632 MonoThreadInfo *info;
633 if (!mono_threads_inited)
635 /* This can happen from DllMain(THREAD_DETACH) on Windows, if a thread
636 * is created before an embedding API user initialized Mono. */
637 THREADS_DEBUG ("mono_thread_info_detach called before mono_threads_init\n");
640 info = (MonoThreadInfo *) mono_native_tls_get_value (thread_info_key);
642 THREADS_DEBUG ("detaching %p\n", info);
643 unregister_thread (info);
644 mono_native_tls_set_value (thread_info_key, NULL);
649 * mono_thread_info_is_exiting:
651 * Return whenever the current thread is exiting, i.e. it is running pthread
655 mono_thread_info_is_exiting (void)
657 #if defined(__MACH__)
658 if (mono_native_tls_get_value (thread_exited_key) == GUINT_TO_POINTER (1))
666 thread_info_key_dtor (void *arg)
668 /* Put the MonoThreadInfo back for the duration of the
669 * unregister code. In some circumstances the thread needs to
670 * take the GC lock which may block which requires a coop
671 * state transition. */
672 mono_native_tls_set_value (thread_info_key, arg);
673 unregister_thread (arg);
674 mono_native_tls_set_value (thread_info_key, NULL);
679 mono_threads_init (MonoThreadInfoCallbacks *callbacks, size_t info_size)
682 threads_callbacks = *callbacks;
683 thread_info_size = info_size;
686 res = mono_native_tls_alloc (&thread_info_key, NULL);
687 res = mono_native_tls_alloc (&thread_exited_key, NULL);
689 res = mono_native_tls_alloc (&thread_info_key, (void *) thread_info_key_dtor);
690 res = mono_native_tls_alloc (&thread_exited_key, (void *) thread_exited_dtor);
695 #ifndef HAVE_KW_THREAD
696 res = mono_native_tls_alloc (&small_id_key, NULL);
700 if ((sleepLimit = g_getenv ("MONO_SLEEP_ABORT_LIMIT")) != NULL) {
702 long threshold = strtol(sleepLimit, NULL, 10);
703 if ((errno == 0) && (threshold >= 40)) {
704 sleepAbortDuration = threshold;
705 sleepWarnDuration = threshold / 20;
707 g_warning("MONO_SLEEP_ABORT_LIMIT must be a number >= 40");
711 mono_os_sem_init (&global_suspend_semaphore, 1);
712 mono_os_sem_init (&suspend_semaphore, 0);
713 mono_os_mutex_init (&join_mutex);
715 mono_lls_init (&thread_list, NULL);
716 mono_thread_smr_init ();
717 mono_threads_suspend_init ();
718 mono_threads_coop_init ();
719 mono_threads_platform_init ();
721 #if defined(__MACH__)
722 mono_mach_init (thread_info_key);
725 mono_threads_inited = TRUE;
727 g_assert (sizeof (MonoNativeThreadId) <= sizeof (uintptr_t));
731 mono_threads_signals_init (void)
733 mono_threads_suspend_init_signals ();
737 mono_threads_runtime_init (MonoThreadInfoRuntimeCallbacks *callbacks)
739 runtime_callbacks = *callbacks;
742 MonoThreadInfoRuntimeCallbacks *
743 mono_threads_get_runtime_callbacks (void)
745 return &runtime_callbacks;
749 mono_thread_info_core_resume (MonoThreadInfo *info)
751 gboolean res = FALSE;
753 switch (mono_threads_transition_request_resume (info)) {
760 case ResumeInitSelfResume:
761 resume_self_suspended (info);
764 case ResumeInitAsyncResume:
765 resume_async_suspended (info);
768 case ResumeInitBlockingResume:
769 resume_blocking_suspended (info);
778 mono_thread_info_resume (MonoNativeThreadId tid)
780 gboolean result; /* don't initialize it so the compiler can catch unitilized paths. */
781 MonoThreadHazardPointers *hp = mono_hazard_pointer_get ();
782 MonoThreadInfo *info;
784 THREADS_SUSPEND_DEBUG ("RESUMING tid %p\n", (void*)tid);
786 mono_thread_info_suspend_lock ();
788 info = mono_thread_info_lookup (tid); /*info on HP1*/
794 result = mono_thread_info_core_resume (info);
796 //Wait for the pending resume to finish
797 mono_threads_wait_pending_operations ();
800 mono_thread_info_suspend_unlock ();
801 mono_hazard_pointer_clear (hp, 1);
806 mono_thread_info_begin_suspend (MonoThreadInfo *info)
808 switch (mono_threads_transition_request_async_suspension (info)) {
809 case AsyncSuspendAlreadySuspended:
810 case AsyncSuspendBlocking:
812 case AsyncSuspendWait:
813 mono_threads_add_to_pending_operation_set (info);
815 case AsyncSuspendInitSuspend:
816 return begin_async_suspend (info, FALSE);
818 g_assert_not_reached ();
823 mono_thread_info_begin_resume (MonoThreadInfo *info)
825 return mono_thread_info_core_resume (info);
829 FIXME fix cardtable WB to be out of line and check with the runtime if the target is not the
830 WB trampoline. Another option is to encode wb ranges in MonoJitInfo, but that is somewhat hard.
833 is_thread_in_critical_region (MonoThreadInfo *info)
837 gpointer stack_start;
838 MonoThreadUnwindState *state;
840 if (mono_threads_platform_in_critical_region (mono_thread_info_get_tid (info)))
843 /* Are we inside a system critical region? */
844 if (info->inside_critical_region)
847 /* Are we inside a GC critical region? */
848 if (threads_callbacks.mono_thread_in_critical_region && threads_callbacks.mono_thread_in_critical_region (info)) {
852 /* The target thread might be shutting down and the domain might be null, which means no managed code left to run. */
853 state = mono_thread_info_get_suspend_state (info);
854 if (!state->unwind_data [MONO_UNWIND_DATA_DOMAIN])
857 stack_start = MONO_CONTEXT_GET_SP (&state->ctx);
858 /* altstack signal handler, sgen can't handle them, so we treat them as critical */
859 if (stack_start < info->stack_start_limit || stack_start >= info->stack_end)
862 if (threads_callbacks.ip_in_critical_region)
863 return threads_callbacks.ip_in_critical_region ((MonoDomain *) state->unwind_data [MONO_UNWIND_DATA_DOMAIN], (char *) MONO_CONTEXT_GET_IP (&state->ctx));
865 ji = mono_jit_info_table_find (
866 (MonoDomain *) state->unwind_data [MONO_UNWIND_DATA_DOMAIN],
867 (char *) MONO_CONTEXT_GET_IP (&state->ctx));
872 method = mono_jit_info_get_method (ji);
874 return threads_callbacks.mono_method_is_critical (method);
878 mono_thread_info_in_critical_location (MonoThreadInfo *info)
880 return is_thread_in_critical_region (info);
884 The return value is only valid until a matching mono_thread_info_resume is called
886 static MonoThreadInfo*
887 suspend_sync (MonoNativeThreadId tid, gboolean interrupt_kernel)
889 MonoThreadHazardPointers *hp = mono_hazard_pointer_get ();
890 MonoThreadInfo *info = mono_thread_info_lookup (tid); /*info on HP1*/
894 switch (mono_threads_transition_request_async_suspension (info)) {
895 case AsyncSuspendAlreadySuspended:
896 mono_hazard_pointer_clear (hp, 1); //XXX this is questionable we got to clean the suspend/resume nonsense of critical sections
898 case AsyncSuspendWait:
899 mono_threads_add_to_pending_operation_set (info);
901 case AsyncSuspendInitSuspend:
902 if (!begin_async_suspend (info, interrupt_kernel)) {
903 mono_hazard_pointer_clear (hp, 1);
907 case AsyncSuspendBlocking:
908 if (interrupt_kernel)
909 mono_threads_suspend_abort_syscall (info);
913 g_assert_not_reached ();
916 //Wait for the pending suspend to finish
917 mono_threads_wait_pending_operations ();
919 if (!check_async_suspend (info)) {
920 mono_thread_info_core_resume (info);
921 mono_threads_wait_pending_operations ();
922 mono_hazard_pointer_clear (hp, 1);
928 static MonoThreadInfo*
929 suspend_sync_nolock (MonoNativeThreadId id, gboolean interrupt_kernel)
931 MonoThreadInfo *info = NULL;
932 int sleep_duration = 0;
934 if (!(info = suspend_sync (id, interrupt_kernel))) {
935 mono_hazard_pointer_clear (mono_hazard_pointer_get (), 1);
939 /*WARNING: We now are in interrupt context until we resume the thread. */
940 if (!is_thread_in_critical_region (info))
943 if (!mono_thread_info_core_resume (info)) {
944 mono_hazard_pointer_clear (mono_hazard_pointer_get (), 1);
947 THREADS_SUSPEND_DEBUG ("RESTARTED thread tid %p\n", (void*)id);
949 /* Wait for the pending resume to finish */
950 mono_threads_wait_pending_operations ();
952 if (sleep_duration == 0)
953 mono_thread_info_yield ();
955 g_usleep (sleep_duration);
957 sleep_duration += 10;
963 mono_thread_info_safe_suspend_and_run (MonoNativeThreadId id, gboolean interrupt_kernel, MonoSuspendThreadCallback callback, gpointer user_data)
966 MonoThreadInfo *info = NULL;
967 MonoThreadHazardPointers *hp = mono_hazard_pointer_get ();
969 THREADS_SUSPEND_DEBUG ("SUSPENDING tid %p\n", (void*)id);
970 /*FIXME: unify this with self-suspend*/
971 g_assert (id != mono_native_thread_id_get ());
973 /* This can block during stw */
974 mono_thread_info_suspend_lock ();
975 mono_threads_begin_global_suspend ();
977 info = suspend_sync_nolock (id, interrupt_kernel);
981 switch (result = callback (info, user_data)) {
982 case MonoResumeThread:
983 mono_hazard_pointer_set (hp, 1, info);
984 mono_thread_info_core_resume (info);
985 mono_threads_wait_pending_operations ();
988 g_assert (!mono_threads_is_coop_enabled ());
991 g_error ("Invalid suspend_and_run callback return value %d", result);
995 mono_hazard_pointer_clear (hp, 1);
996 mono_threads_end_global_suspend ();
997 mono_thread_info_suspend_unlock ();
1001 Inject an assynchronous call into the target thread. The target thread must be suspended and
1002 only a single async call can be setup for a given suspend cycle.
1003 This async call must cause stack unwinding as the current implementation doesn't save enough state
1004 to resume execution of the top-of-stack function. It's an acceptable limitation since this is
1005 currently used only to deliver exceptions.
1008 mono_thread_info_setup_async_call (MonoThreadInfo *info, void (*target_func)(void*), void *user_data)
1010 if (!mono_threads_is_coop_enabled ()) {
1011 /* In non-coop mode, an async call can only be setup on an async suspended thread, but in coop mode, a thread
1012 * may be in blocking state, and will execute the async call when leaving the safepoint, leaving a gc safe
1013 * region or entering a gc unsafe region */
1014 g_assert (mono_thread_info_run_state (info) == STATE_ASYNC_SUSPENDED);
1016 /*FIXME this is a bad assert, we probably should do proper locking and fail if one is already set*/
1017 g_assert (!info->async_target);
1018 info->async_target = target_func;
1019 /* This is not GC tracked */
1020 info->user_data = user_data;
1024 The suspend lock is held during any suspend in progress.
1025 A GC that has safepoints must take this lock as part of its
1026 STW to make sure no unsafe pending suspend is in progress.
1030 mono_thread_info_suspend_lock_with_info (MonoThreadInfo *info)
1033 g_assert (mono_thread_info_is_current (info));
1034 g_assert (mono_thread_info_is_live (info));
1036 MONO_ENTER_GC_SAFE_WITH_INFO(info);
1038 int res = mono_os_sem_wait (&global_suspend_semaphore, MONO_SEM_FLAGS_NONE);
1039 g_assert (res != -1);
1041 MONO_EXIT_GC_SAFE_WITH_INFO;
1045 mono_thread_info_suspend_lock (void)
1047 mono_thread_info_suspend_lock_with_info (mono_thread_info_current_unchecked ());
1051 mono_thread_info_suspend_unlock (void)
1053 mono_os_sem_post (&global_suspend_semaphore);
1057 * This is a very specific function whose only purpose is to
1058 * break a given thread from socket syscalls.
1060 * This only exists because linux won't fail a call to connect
1061 * if the underlying is closed.
1063 * TODO We should cleanup and unify this with the other syscall abort
1067 mono_thread_info_abort_socket_syscall_for_close (MonoNativeThreadId tid)
1069 MonoThreadHazardPointers *hp;
1070 MonoThreadInfo *info;
1072 if (tid == mono_native_thread_id_get ())
1075 hp = mono_hazard_pointer_get ();
1076 info = mono_thread_info_lookup (tid);
1080 if (mono_thread_info_run_state (info) == STATE_DETACHED) {
1081 mono_hazard_pointer_clear (hp, 1);
1085 mono_thread_info_suspend_lock ();
1086 mono_threads_begin_global_suspend ();
1088 mono_threads_suspend_abort_syscall (info);
1089 mono_threads_wait_pending_operations ();
1091 mono_hazard_pointer_clear (hp, 1);
1093 mono_threads_end_global_suspend ();
1094 mono_thread_info_suspend_unlock ();
1098 * mono_thread_info_set_is_async_context:
1100 * Set whenever the current thread is in an async context. Some runtime functions might behave
1101 * differently while in an async context in order to be async safe.
1104 mono_thread_info_set_is_async_context (gboolean async_context)
1106 MonoThreadInfo *info = mono_thread_info_current ();
1109 info->is_async_context = async_context;
1113 mono_thread_info_is_async_context (void)
1115 MonoThreadInfo *info = mono_thread_info_current ();
1118 return info->is_async_context;
1124 * mono_thread_info_get_stack_bounds:
1126 * Return the address and size of the current threads stack. Return NULL as the
1127 * stack address if the stack address cannot be determined.
1130 mono_thread_info_get_stack_bounds (guint8 **staddr, size_t *stsize)
1132 guint8 *current = (guint8 *)&stsize;
1133 mono_threads_platform_get_stack_bounds (staddr, stsize);
1137 /* Sanity check the result */
1138 g_assert ((current > *staddr) && (current < *staddr + *stsize));
1140 /* When running under emacs, sometimes staddr is not aligned to a page size */
1141 *staddr = (guint8*)((gssize)*staddr & ~(mono_pagesize () - 1));
1145 mono_thread_info_yield (void)
1147 return mono_threads_platform_yield ();
1150 static mono_lazy_init_t sleep_init = MONO_LAZY_INIT_STATUS_NOT_INITIALIZED;
1151 static MonoCoopMutex sleep_mutex;
1152 static MonoCoopCond sleep_cond;
1155 sleep_initialize (void)
1157 mono_coop_mutex_init (&sleep_mutex);
1158 mono_coop_cond_init (&sleep_cond);
1162 sleep_interrupt (gpointer data)
1164 mono_coop_mutex_lock (&sleep_mutex);
1165 mono_coop_cond_broadcast (&sleep_cond);
1166 mono_coop_mutex_unlock (&sleep_mutex);
1169 static inline guint32
1170 sleep_interruptable (guint32 ms, gboolean *alerted)
1174 g_assert (MONO_INFINITE_WAIT == G_MAXUINT32);
1179 if (ms != MONO_INFINITE_WAIT)
1180 end = mono_msec_ticks() + ms;
1182 mono_lazy_initialize (&sleep_init, sleep_initialize);
1184 mono_coop_mutex_lock (&sleep_mutex);
1187 if (ms != MONO_INFINITE_WAIT) {
1188 now = mono_msec_ticks();
1193 mono_thread_info_install_interrupt (sleep_interrupt, NULL, alerted);
1195 mono_coop_mutex_unlock (&sleep_mutex);
1196 return WAIT_IO_COMPLETION;
1199 if (ms != MONO_INFINITE_WAIT)
1200 mono_coop_cond_timedwait (&sleep_cond, &sleep_mutex, end - now);
1202 mono_coop_cond_wait (&sleep_cond, &sleep_mutex);
1204 mono_thread_info_uninstall_interrupt (alerted);
1206 mono_coop_mutex_unlock (&sleep_mutex);
1207 return WAIT_IO_COMPLETION;
1211 mono_coop_mutex_unlock (&sleep_mutex);
1217 mono_thread_info_sleep (guint32 ms, gboolean *alerted)
1220 MonoThreadInfo *info;
1222 mono_thread_info_yield ();
1224 info = mono_thread_info_current ();
1225 if (info && mono_thread_info_is_interrupt_state (info))
1226 return WAIT_IO_COMPLETION;
1232 return sleep_interruptable (ms, alerted);
1236 if (ms == MONO_INFINITE_WAIT) {
1239 Sleep (G_MAXUINT32);
1241 sleep (G_MAXUINT32);
1246 #if defined (__linux__) && !defined(PLATFORM_ANDROID)
1247 struct timespec start, target;
1249 /* Use clock_nanosleep () to prevent time drifting problems when nanosleep () is interrupted by signals */
1250 ret = clock_gettime (CLOCK_MONOTONIC, &start);
1251 g_assert (ret == 0);
1254 target.tv_sec += ms / 1000;
1255 target.tv_nsec += (ms % 1000) * 1000000;
1256 if (target.tv_nsec > 999999999) {
1257 target.tv_nsec -= 999999999;
1262 ret = clock_nanosleep (CLOCK_MONOTONIC, TIMER_ABSTIME, &target, NULL);
1267 struct timespec req, rem;
1269 req.tv_sec = ms / 1000;
1270 req.tv_nsec = (ms % 1000) * 1000000;
1273 memset (&rem, 0, sizeof (rem));
1274 ret = nanosleep (&req, &rem);
1276 #endif /* __linux__ */
1285 mono_thread_info_usleep (guint64 us)
1294 mono_thread_info_tls_get (THREAD_INFO_TYPE *info, MonoTlsKey key)
1296 return ((MonoThreadInfo*)info)->tls [key];
1300 * mono_threads_info_tls_set:
1302 * Set the TLS key to VALUE in the info structure. This can be used to obtain
1303 * values of TLS variables for threads other than the current thread.
1304 * This should only be used for infrequently changing TLS variables, and it should
1305 * be paired with setting the real TLS variable since this provides no GC tracking.
1308 mono_thread_info_tls_set (THREAD_INFO_TYPE *info, MonoTlsKey key, gpointer value)
1310 ((MonoThreadInfo*)info)->tls [key] = value;
1313 #if defined(__native_client__)
1314 void nacl_shutdown_gc_thread(void);
1318 * mono_thread_info_exit:
1320 * Exit the current thread.
1321 * This function doesn't return.
1324 mono_thread_info_exit (gsize exit_code)
1326 #if defined(__native_client__)
1327 nacl_shutdown_gc_thread();
1330 mono_thread_info_detach ();
1332 mono_threads_platform_exit (0);
1336 * mono_threads_open_thread_handle:
1338 * Duplicate the handle. The handle needs to be closed by calling
1339 * mono_threads_close_thread_handle () when it is no longer needed.
1342 mono_threads_open_thread_handle (MonoThreadHandle *thread_handle)
1344 return mono_refcount_inc (thread_handle);
1348 mono_threads_close_thread_handle (MonoThreadHandle *thread_handle)
1350 mono_refcount_dec (thread_handle);
1354 mono_threads_signal_thread_handle (MonoThreadHandle* thread_handle)
1356 mono_os_event_set (&thread_handle->event);
1359 #define INTERRUPT_STATE ((MonoThreadInfoInterruptToken*) (size_t) -1)
1361 struct _MonoThreadInfoInterruptToken {
1362 void (*callback) (gpointer data);
1367 * mono_thread_info_install_interrupt: install an interruption token for the current thread.
1369 * - @callback: must be able to be called from another thread and always cancel the wait
1370 * - @data: passed to the callback
1371 * - @interrupted: will be set to TRUE if a token is already installed, FALSE otherwise
1372 * if set to TRUE, it must mean that the thread is in interrupted state
1375 mono_thread_info_install_interrupt (void (*callback) (gpointer data), gpointer data, gboolean *interrupted)
1377 MonoThreadInfo *info;
1378 MonoThreadInfoInterruptToken *previous_token, *token;
1380 g_assert (callback);
1382 g_assert (interrupted);
1383 *interrupted = FALSE;
1385 info = mono_thread_info_current ();
1388 /* The memory of this token can be freed at 2 places:
1389 * - if the token is not interrupted: it will be freed in uninstall, as info->interrupt_token has not been replaced
1390 * by the INTERRUPT_STATE flag value, and it still contains the pointer to the memory location
1391 * - if the token is interrupted: it will be freed in finish, as the token is now owned by the prepare/finish
1392 * functions, and info->interrupt_token does not contains a pointer to the memory anymore */
1393 token = g_new0 (MonoThreadInfoInterruptToken, 1);
1394 token->callback = callback;
1397 previous_token = (MonoThreadInfoInterruptToken *)InterlockedCompareExchangePointer ((gpointer*) &info->interrupt_token, token, NULL);
1399 if (previous_token) {
1400 if (previous_token != INTERRUPT_STATE)
1401 g_error ("mono_thread_info_install_interrupt: previous_token should be INTERRUPT_STATE (%p), but it was %p", INTERRUPT_STATE, previous_token);
1405 *interrupted = TRUE;
1408 THREADS_INTERRUPT_DEBUG ("interrupt install tid %p token %p previous_token %p interrupted %s\n",
1409 mono_thread_info_get_tid (info), token, previous_token, *interrupted ? "TRUE" : "FALSE");
1413 mono_thread_info_uninstall_interrupt (gboolean *interrupted)
1415 MonoThreadInfo *info;
1416 MonoThreadInfoInterruptToken *previous_token;
1418 g_assert (interrupted);
1419 *interrupted = FALSE;
1421 info = mono_thread_info_current ();
1424 previous_token = (MonoThreadInfoInterruptToken *)InterlockedExchangePointer ((gpointer*) &info->interrupt_token, NULL);
1426 /* only the installer can uninstall the token */
1427 g_assert (previous_token);
1429 if (previous_token == INTERRUPT_STATE) {
1430 /* if it is interrupted, then it is going to be freed in finish interrupt */
1431 *interrupted = TRUE;
1433 g_free (previous_token);
1436 THREADS_INTERRUPT_DEBUG ("interrupt uninstall tid %p previous_token %p interrupted %s\n",
1437 mono_thread_info_get_tid (info), previous_token, *interrupted ? "TRUE" : "FALSE");
1440 static MonoThreadInfoInterruptToken*
1441 set_interrupt_state (MonoThreadInfo *info)
1443 MonoThreadInfoInterruptToken *token, *previous_token;
1447 /* Atomically obtain the token the thread is
1448 * waiting on, and change it to a flag value. */
1451 previous_token = info->interrupt_token;
1453 /* Already interrupted */
1454 if (previous_token == INTERRUPT_STATE) {
1459 token = previous_token;
1460 } while (InterlockedCompareExchangePointer ((gpointer*) &info->interrupt_token, INTERRUPT_STATE, previous_token) != previous_token);
1466 * mono_thread_info_prepare_interrupt:
1468 * The state of the thread info interrupt token is set to 'interrupted' which means that :
1469 * - if the thread calls one of the WaitFor functions, the function will return with
1470 * WAIT_IO_COMPLETION instead of waiting
1471 * - if the thread was waiting when this function was called, the wait will be broken
1473 * It is possible that the wait functions return WAIT_IO_COMPLETION, but the target thread
1474 * didn't receive the interrupt signal yet, in this case it should call the wait function
1475 * again. This essentially means that the target thread will busy wait until it is ready to
1476 * process the interruption.
1478 MonoThreadInfoInterruptToken*
1479 mono_thread_info_prepare_interrupt (MonoThreadInfo *info)
1481 MonoThreadInfoInterruptToken *token;
1483 token = set_interrupt_state (info);
1485 THREADS_INTERRUPT_DEBUG ("interrupt prepare tid %p token %p\n",
1486 mono_thread_info_get_tid (info), token);
1492 mono_thread_info_finish_interrupt (MonoThreadInfoInterruptToken *token)
1494 THREADS_INTERRUPT_DEBUG ("interrupt finish token %p\n", token);
1499 g_assert (token->callback);
1501 token->callback (token->data);
1507 mono_thread_info_self_interrupt (void)
1509 MonoThreadInfo *info;
1510 MonoThreadInfoInterruptToken *token;
1512 info = mono_thread_info_current ();
1515 token = set_interrupt_state (info);
1518 THREADS_INTERRUPT_DEBUG ("interrupt self tid %p\n",
1519 mono_thread_info_get_tid (info));
1522 /* Clear the interrupted flag of the current thread, set with
1523 * mono_thread_info_self_interrupt, so it can wait again */
1525 mono_thread_info_clear_self_interrupt ()
1527 MonoThreadInfo *info;
1528 MonoThreadInfoInterruptToken *previous_token;
1530 info = mono_thread_info_current ();
1533 previous_token = (MonoThreadInfoInterruptToken *)InterlockedCompareExchangePointer ((gpointer*) &info->interrupt_token, NULL, INTERRUPT_STATE);
1534 g_assert (previous_token == NULL || previous_token == INTERRUPT_STATE);
1536 THREADS_INTERRUPT_DEBUG ("interrupt clear self tid %p previous_token %p\n", mono_thread_info_get_tid (info), previous_token);
1540 mono_thread_info_is_interrupt_state (MonoThreadInfo *info)
1543 return InterlockedReadPointer ((gpointer*) &info->interrupt_token) == INTERRUPT_STATE;
1547 mono_thread_info_describe_interrupt_token (MonoThreadInfo *info, GString *text)
1551 if (!InterlockedReadPointer ((gpointer*) &info->interrupt_token))
1552 g_string_append_printf (text, "not waiting");
1553 else if (InterlockedReadPointer ((gpointer*) &info->interrupt_token) == INTERRUPT_STATE)
1554 g_string_append_printf (text, "interrupted state");
1556 g_string_append_printf (text, "waiting");
1560 mono_thread_info_is_current (MonoThreadInfo *info)
1562 return mono_thread_info_get_tid (info) == mono_native_thread_id_get ();
1565 MonoThreadInfoWaitRet
1566 mono_thread_info_wait_one_handle (MonoThreadHandle *thread_handle, guint32 timeout, gboolean alertable)
1568 MonoOSEventWaitRet res;
1570 res = mono_os_event_wait_one (&thread_handle->event, timeout, alertable);
1571 if (res == MONO_OS_EVENT_WAIT_RET_SUCCESS_0)
1572 return MONO_THREAD_INFO_WAIT_RET_SUCCESS_0;
1573 else if (res == MONO_OS_EVENT_WAIT_RET_ALERTED)
1574 return MONO_THREAD_INFO_WAIT_RET_ALERTED;
1575 else if (res == MONO_OS_EVENT_WAIT_RET_TIMEOUT)
1576 return MONO_THREAD_INFO_WAIT_RET_TIMEOUT;
1578 g_error ("%s: unknown res value %d", __func__, res);
1581 MonoThreadInfoWaitRet
1582 mono_thread_info_wait_multiple_handle (MonoThreadHandle **thread_handles, gsize nhandles, MonoOSEvent *background_change_event, gboolean waitall, guint32 timeout, gboolean alertable)
1584 MonoOSEventWaitRet res;
1585 MonoOSEvent *thread_events [MONO_OS_EVENT_WAIT_MAXIMUM_OBJECTS];
1588 g_assert (nhandles <= MONO_OS_EVENT_WAIT_MAXIMUM_OBJECTS);
1589 if (background_change_event)
1590 g_assert (nhandles <= MONO_OS_EVENT_WAIT_MAXIMUM_OBJECTS - 1);
1592 for (i = 0; i < nhandles; ++i)
1593 thread_events [i] = &thread_handles [i]->event;
1595 if (background_change_event)
1596 thread_events [nhandles ++] = background_change_event;
1598 res = mono_os_event_wait_multiple (thread_events, nhandles, waitall, timeout, alertable);
1599 if (res >= MONO_OS_EVENT_WAIT_RET_SUCCESS_0 && res <= MONO_OS_EVENT_WAIT_RET_SUCCESS_0 + nhandles - 1)
1600 return MONO_THREAD_INFO_WAIT_RET_SUCCESS_0 + (res - MONO_OS_EVENT_WAIT_RET_SUCCESS_0);
1601 else if (res == MONO_OS_EVENT_WAIT_RET_ALERTED)
1602 return MONO_THREAD_INFO_WAIT_RET_ALERTED;
1603 else if (res == MONO_OS_EVENT_WAIT_RET_TIMEOUT)
1604 return MONO_THREAD_INFO_WAIT_RET_TIMEOUT;
1606 g_error ("%s: unknown res value %d", __func__, res);
1610 * mono_threads_join_mutex:
1612 * This mutex is used to avoid races between pthread_create () and pthread_join () on osx, see
1613 * https://bugzilla.xamarin.com/show_bug.cgi?id=50529
1614 * The code inside the lock should not block.
1617 mono_threads_join_lock (void)
1620 mono_os_mutex_lock (&join_mutex);
1625 mono_threads_join_unlock (void)
1628 mono_os_mutex_unlock (&join_mutex);