Skip to content
Find file
Fetching contributors…
Cannot retrieve contributors at this time
1354 lines (1155 sloc) 37.3 KB
/*
* monitor.c: Monitor locking functions
*
* Author:
* Dick Porter (dick@ximian.com)
*
* Copyright 2003 Ximian, Inc (http://www.ximian.com)
* Copyright 2004-2009 Novell, Inc (http://www.novell.com)
* Licensed under the MIT license. See LICENSE file in the project root for full license information.
*/
#include <config.h>
#include <glib.h>
#include <string.h>
#include <mono/metadata/abi-details.h>
#include <mono/metadata/monitor.h>
#include <mono/metadata/threads-types.h>
#include <mono/metadata/exception.h>
#include <mono/metadata/threads.h>
#include <mono/io-layer/io-layer.h>
#include <mono/metadata/object-internals.h>
#include <mono/metadata/class-internals.h>
#include <mono/metadata/gc-internals.h>
#include <mono/metadata/method-builder.h>
#include <mono/metadata/debug-helpers.h>
#include <mono/metadata/tabledefs.h>
#include <mono/metadata/marshal.h>
#include <mono/utils/mono-threads.h>
#include <mono/metadata/profiler-private.h>
#include <mono/utils/mono-time.h>
#include <mono/utils/atomic.h>
/*
* Pull the list of opcodes
*/
#define OPDEF(a,b,c,d,e,f,g,h,i,j) \
a = i,
enum {
#include "mono/cil/opcode.def"
LAST = 0xff
};
#undef OPDEF
/*#define LOCK_DEBUG(a) do { a; } while (0)*/
#define LOCK_DEBUG(a)
/*
* The monitor implementation here is based on
* http://www.usenix.org/events/jvm01/full_papers/dice/dice.pdf and
* http://www.research.ibm.com/people/d/dfb/papers/Bacon98Thin.ps
*
* The Dice paper describes a technique for saving lock record space
* by returning records to a free list when they become unused. That
* sounds like unnecessary complexity to me, though if it becomes
* clear that unused lock records are taking up lots of space or we
* need to shave more time off by avoiding a malloc then we can always
* implement the free list idea later. The timeout parameter to
* try_enter voids some of the assumptions about the reference count
* field in Dice's implementation too. In his version, the thread
* attempting to lock a contended object will block until it succeeds,
* so the reference count will never be decremented while an object is
* locked.
*
* Bacon's thin locks have a fast path that doesn't need a lock record
* for the common case of locking an unlocked or shallow-nested
* object.
*/
typedef struct _MonitorArray MonitorArray;
struct _MonitorArray {
MonitorArray *next;
int num_monitors;
MonoThreadsSync monitors [MONO_ZERO_LEN_ARRAY];
};
#define mono_monitor_allocator_lock() mono_os_mutex_lock (&monitor_mutex)
#define mono_monitor_allocator_unlock() mono_os_mutex_unlock (&monitor_mutex)
static mono_mutex_t monitor_mutex;
static MonoThreadsSync *monitor_freelist;
static MonitorArray *monitor_allocated;
static int array_size = 16;
/* MonoThreadsSync status helpers */
static inline guint32
mon_status_get_owner (guint32 status)
{
return status & OWNER_MASK;
}
static inline guint32
mon_status_set_owner (guint32 status, guint32 owner)
{
return (status & ENTRY_COUNT_MASK) | owner;
}
static inline gint32
mon_status_get_entry_count (guint32 status)
{
gint32 entry_count = (gint32)((status & ENTRY_COUNT_MASK) >> ENTRY_COUNT_SHIFT);
gint32 zero = (gint32)(((guint32)ENTRY_COUNT_ZERO) >> ENTRY_COUNT_SHIFT);
return entry_count - zero;
}
static inline guint32
mon_status_init_entry_count (guint32 status)
{
return (status & OWNER_MASK) | ENTRY_COUNT_ZERO;
}
static inline guint32
mon_status_increment_entry_count (guint32 status)
{
return status + (1 << ENTRY_COUNT_SHIFT);
}
static inline guint32
mon_status_decrement_entry_count (guint32 status)
{
return status - (1 << ENTRY_COUNT_SHIFT);
}
static inline gboolean
mon_status_have_waiters (guint32 status)
{
return status & ENTRY_COUNT_WAITERS;
}
/* LockWord helpers */
static inline MonoThreadsSync*
lock_word_get_inflated_lock (LockWord lw)
{
lw.lock_word &= (~LOCK_WORD_STATUS_MASK);
return lw.sync;
}
static inline gboolean
lock_word_is_inflated (LockWord lw)
{
return lw.lock_word & LOCK_WORD_INFLATED;
}
static inline gboolean
lock_word_has_hash (LockWord lw)
{
return lw.lock_word & LOCK_WORD_HAS_HASH;
}
static inline LockWord
lock_word_set_has_hash (LockWord lw)
{
LockWord nlw;
nlw.lock_word = lw.lock_word | LOCK_WORD_HAS_HASH;
return nlw;
}
static inline gboolean
lock_word_is_free (LockWord lw)
{
return !lw.lock_word;
}
static inline gboolean
lock_word_is_flat (LockWord lw)
{
/* Return whether the lock is flat or free */
return (lw.lock_word & LOCK_WORD_STATUS_MASK) == LOCK_WORD_FLAT;
}
static inline gint32
lock_word_get_hash (LockWord lw)
{
return (gint32) (lw.lock_word >> LOCK_WORD_HASH_SHIFT);
}
static inline gint32
lock_word_get_nest (LockWord lw)
{
if (lock_word_is_free (lw))
return 0;
/* Inword nest count starts from 0 */
return ((lw.lock_word & LOCK_WORD_NEST_MASK) >> LOCK_WORD_NEST_SHIFT) + 1;
}
static inline gboolean
lock_word_is_nested (LockWord lw)
{
return lw.lock_word & LOCK_WORD_NEST_MASK;
}
static inline gboolean
lock_word_is_max_nest (LockWord lw)
{
return (lw.lock_word & LOCK_WORD_NEST_MASK) == LOCK_WORD_NEST_MASK;
}
static inline LockWord
lock_word_increment_nest (LockWord lw)
{
lw.lock_word += 1 << LOCK_WORD_NEST_SHIFT;
return lw;
}
static inline LockWord
lock_word_decrement_nest (LockWord lw)
{
lw.lock_word -= 1 << LOCK_WORD_NEST_SHIFT;
return lw;
}
static inline gint32
lock_word_get_owner (LockWord lw)
{
return lw.lock_word >> LOCK_WORD_OWNER_SHIFT;
}
static inline LockWord
lock_word_new_thin_hash (gint32 hash)
{
LockWord lw;
lw.lock_word = (guint32)hash;
lw.lock_word = (lw.lock_word << LOCK_WORD_HASH_SHIFT) | LOCK_WORD_HAS_HASH;
return lw;
}
static inline LockWord
lock_word_new_inflated (MonoThreadsSync *mon)
{
LockWord lw;
lw.sync = mon;
lw.lock_word |= LOCK_WORD_INFLATED;
return lw;
}
static inline LockWord
lock_word_new_flat (gint32 owner)
{
LockWord lw;
lw.lock_word = owner;
lw.lock_word <<= LOCK_WORD_OWNER_SHIFT;
return lw;
}
void
mono_monitor_init (void)
{
mono_os_mutex_init_recursive (&monitor_mutex);
}
void
mono_monitor_cleanup (void)
{
MonoThreadsSync *mon;
/* MonitorArray *marray, *next = NULL; */
/*mono_os_mutex_destroy (&monitor_mutex);*/
/* The monitors on the freelist don't have weak links - mark them */
for (mon = monitor_freelist; mon; mon = (MonoThreadsSync *)mon->data)
mon->wait_list = (GSList *)-1;
/*
* FIXME: This still crashes with sgen (async_read.exe)
*
* In mini_cleanup() we first call mono_runtime_cleanup(), which calls
* mono_monitor_cleanup(), which is supposed to free all monitor memory.
*
* Later in mini_cleanup(), we call mono_domain_free(), which calls
* mono_gc_clear_domain(), which frees all weak links associated with objects.
* Those weak links reside in the monitor structures, which we've freed earlier.
*
* Unless we fix this dependency in the shutdown sequence this code has to remain
* disabled, or at least the call to g_free().
*/
/*
for (marray = monitor_allocated; marray; marray = next) {
int i;
for (i = 0; i < marray->num_monitors; ++i) {
mon = &marray->monitors [i];
if (mon->wait_list != (gpointer)-1)
mono_gc_weak_link_remove (&mon->data);
}
next = marray->next;
g_free (marray);
}
*/
}
static int
monitor_is_on_freelist (MonoThreadsSync *mon)
{
MonitorArray *marray;
for (marray = monitor_allocated; marray; marray = marray->next) {
if (mon >= marray->monitors && mon < &marray->monitors [marray->num_monitors])
return TRUE;
}
return FALSE;
}
/**
* mono_locks_dump:
* @include_untaken:
*
* Print a report on stdout of the managed locks currently held by
* threads. If @include_untaken is specified, list also inflated locks
* which are unheld.
* This is supposed to be used in debuggers like gdb.
*/
void
mono_locks_dump (gboolean include_untaken)
{
int i;
int used = 0, on_freelist = 0, to_recycle = 0, total = 0, num_arrays = 0;
MonoThreadsSync *mon;
MonitorArray *marray;
for (mon = monitor_freelist; mon; mon = (MonoThreadsSync *)mon->data)
on_freelist++;
for (marray = monitor_allocated; marray; marray = marray->next) {
total += marray->num_monitors;
num_arrays++;
for (i = 0; i < marray->num_monitors; ++i) {
mon = &marray->monitors [i];
if (mon->data == NULL) {
if (i < marray->num_monitors - 1)
to_recycle++;
} else {
if (!monitor_is_on_freelist ((MonoThreadsSync *)mon->data)) {
MonoObject *holder = (MonoObject *)mono_gchandle_get_target ((guint32)mon->data);
if (mon_status_get_owner (mon->status)) {
g_print ("Lock %p in object %p held by thread %d, nest level: %d\n",
mon, holder, mon_status_get_owner (mon->status), mon->nest);
if (mon->entry_sem)
g_print ("\tWaiting on semaphore %p: %d\n", mon->entry_sem, mon_status_get_entry_count (mon->status));
} else if (include_untaken) {
g_print ("Lock %p in object %p untaken\n", mon, holder);
}
used++;
}
}
}
}
g_print ("Total locks (in %d array(s)): %d, used: %d, on freelist: %d, to recycle: %d\n",
num_arrays, total, used, on_freelist, to_recycle);
}
/* LOCKING: this is called with monitor_mutex held */
static void
mon_finalize (MonoThreadsSync *mon)
{
LOCK_DEBUG (g_message ("%s: Finalizing sync %p", __func__, mon));
if (mon->entry_sem != NULL) {
CloseHandle (mon->entry_sem);
mon->entry_sem = NULL;
}
/* If this isn't empty then something is seriously broken - it
* means a thread is still waiting on the object that owned
* this lock, but the object has been finalized.
*/
g_assert (mon->wait_list == NULL);
/* owner and nest are set in mon_new, no need to zero them out */
mon->data = monitor_freelist;
monitor_freelist = mon;
#ifndef DISABLE_PERFCOUNTERS
mono_perfcounters->gc_sync_blocks--;
#endif
}
/* LOCKING: this is called with monitor_mutex held */
static MonoThreadsSync *
mon_new (gsize id)
{
MonoThreadsSync *new_;
if (!monitor_freelist) {
MonitorArray *marray;
int i;
/* see if any sync block has been collected */
new_ = NULL;
for (marray = monitor_allocated; marray; marray = marray->next) {
for (i = 0; i < marray->num_monitors; ++i) {
if (mono_gchandle_get_target ((guint32)marray->monitors [i].data) == NULL) {
new_ = &marray->monitors [i];
if (new_->wait_list) {
/* Orphaned events left by aborted threads */
while (new_->wait_list) {
LOCK_DEBUG (g_message (G_GNUC_PRETTY_FUNCTION ": (%d): Closing orphaned event %d", mono_thread_info_get_small_id (), new_->wait_list->data));
CloseHandle (new_->wait_list->data);
new_->wait_list = g_slist_remove (new_->wait_list, new_->wait_list->data);
}
}
mono_gchandle_free ((guint32)new_->data);
new_->data = monitor_freelist;
monitor_freelist = new_;
}
}
/* small perf tweak to avoid scanning all the blocks */
if (new_)
break;
}
/* need to allocate a new array of monitors */
if (!monitor_freelist) {
MonitorArray *last;
LOCK_DEBUG (g_message ("%s: allocating more monitors: %d", __func__, array_size));
marray = (MonitorArray *)g_malloc0 (MONO_SIZEOF_MONO_ARRAY + array_size * sizeof (MonoThreadsSync));
marray->num_monitors = array_size;
array_size *= 2;
/* link into the freelist */
for (i = 0; i < marray->num_monitors - 1; ++i) {
marray->monitors [i].data = &marray->monitors [i + 1];
}
marray->monitors [i].data = NULL; /* the last one */
monitor_freelist = &marray->monitors [0];
/* we happend the marray instead of prepending so that
* the collecting loop above will need to scan smaller arrays first
*/
if (!monitor_allocated) {
monitor_allocated = marray;
} else {
last = monitor_allocated;
while (last->next)
last = last->next;
last->next = marray;
}
}
}
new_ = monitor_freelist;
monitor_freelist = (MonoThreadsSync *)new_->data;
new_->status = mon_status_set_owner (0, id);
new_->status = mon_status_init_entry_count (new_->status);
new_->nest = 1;
new_->data = NULL;
#ifndef DISABLE_PERFCOUNTERS
mono_perfcounters->gc_sync_blocks++;
#endif
return new_;
}
static MonoThreadsSync*
alloc_mon (MonoObject *obj, gint32 id)
{
MonoThreadsSync *mon;
mono_monitor_allocator_lock ();
mon = mon_new (id);
mon->data = (void *)(size_t)mono_gchandle_new_weakref (obj, TRUE);
mono_monitor_allocator_unlock ();
return mon;
}
static void
discard_mon (MonoThreadsSync *mon)
{
mono_monitor_allocator_lock ();
mono_gchandle_free ((guint32)mon->data);
mon_finalize (mon);
mono_monitor_allocator_unlock ();
}
static void
mono_monitor_inflate_owned (MonoObject *obj, int id)
{
MonoThreadsSync *mon;
LockWord nlw, old_lw, tmp_lw;
guint32 nest;
old_lw.sync = obj->synchronisation;
LOCK_DEBUG (g_message ("%s: (%d) Inflating owned lock object %p; LW = %p", __func__, id, obj, old_lw.sync));
if (lock_word_is_inflated (old_lw)) {
/* Someone else inflated the lock in the meantime */
return;
}
mon = alloc_mon (obj, id);
nest = lock_word_get_nest (old_lw);
mon->nest = nest;
nlw = lock_word_new_inflated (mon);
mono_memory_write_barrier ();
tmp_lw.sync = (MonoThreadsSync *)InterlockedCompareExchangePointer ((gpointer*)&obj->synchronisation, nlw.sync, old_lw.sync);
if (tmp_lw.sync != old_lw.sync) {
/* Someone else inflated the lock in the meantime */
discard_mon (mon);
}
}
static void
mono_monitor_inflate (MonoObject *obj)
{
MonoThreadsSync *mon;
LockWord nlw, old_lw;
LOCK_DEBUG (g_message ("%s: (%d) Inflating lock object %p; LW = %p", __func__, mono_thread_info_get_small_id (), obj, obj->synchronisation));
mon = alloc_mon (obj, 0);
nlw = lock_word_new_inflated (mon);
old_lw.sync = obj->synchronisation;
for (;;) {
LockWord tmp_lw;
if (lock_word_is_inflated (old_lw)) {
break;
}
#ifdef HAVE_MOVING_COLLECTOR
else if (lock_word_has_hash (old_lw)) {
mon->hash_code = lock_word_get_hash (old_lw);
mon->status = mon_status_set_owner (mon->status, 0);
nlw = lock_word_set_has_hash (nlw);
}
#endif
else if (lock_word_is_free (old_lw)) {
mon->status = mon_status_set_owner (mon->status, 0);
mon->nest = 1;
} else {
/* Lock is flat */
mon->status = mon_status_set_owner (mon->status, lock_word_get_owner (old_lw));
mon->nest = lock_word_get_nest (old_lw);
}
mono_memory_write_barrier ();
tmp_lw.sync = (MonoThreadsSync *)InterlockedCompareExchangePointer ((gpointer*)&obj->synchronisation, nlw.sync, old_lw.sync);
if (tmp_lw.sync == old_lw.sync) {
/* Successfully inflated the lock */
return;
}
old_lw.sync = tmp_lw.sync;
}
/* Someone else inflated the lock before us */
discard_mon (mon);
}
#define MONO_OBJECT_ALIGNMENT_SHIFT 3
/*
* mono_object_hash:
* @obj: an object
*
* Calculate a hash code for @obj that is constant while @obj is alive.
*/
int
mono_object_hash (MonoObject* obj)
{
#ifdef HAVE_MOVING_COLLECTOR
LockWord lw;
unsigned int hash;
if (!obj)
return 0;
lw.sync = obj->synchronisation;
LOCK_DEBUG (g_message("%s: (%d) Get hash for object %p; LW = %p", __func__, mono_thread_info_get_small_id (), obj, obj->synchronisation));
if (lock_word_has_hash (lw)) {
if (lock_word_is_inflated (lw)) {
return lock_word_get_inflated_lock (lw)->hash_code;
} else {
return lock_word_get_hash (lw);
}
}
/*
* while we are inside this function, the GC will keep this object pinned,
* since we are in the unmanaged stack. Thanks to this and to the hash
* function that depends only on the address, we can ignore the races if
* another thread computes the hash at the same time, because it'll end up
* with the same value.
*/
hash = (GPOINTER_TO_UINT (obj) >> MONO_OBJECT_ALIGNMENT_SHIFT) * 2654435761u;
#if SIZEOF_VOID_P == 4
/* clear the top bits as they can be discarded */
hash &= ~(LOCK_WORD_STATUS_MASK << (32 - LOCK_WORD_STATUS_BITS));
#endif
if (lock_word_is_free (lw)) {
LockWord old_lw;
lw = lock_word_new_thin_hash (hash);
old_lw.sync = (MonoThreadsSync *)InterlockedCompareExchangePointer ((gpointer*)&obj->synchronisation, lw.sync, NULL);
if (old_lw.sync == NULL) {
return hash;
}
if (lock_word_has_hash (old_lw)) {
/* Done by somebody else */
return hash;
}
mono_monitor_inflate (obj);
lw.sync = obj->synchronisation;
} else if (lock_word_is_flat (lw)) {
int id = mono_thread_info_get_small_id ();
if (lock_word_get_owner (lw) == id)
mono_monitor_inflate_owned (obj, id);
else
mono_monitor_inflate (obj);
lw.sync = obj->synchronisation;
}
/* At this point, the lock is inflated */
lock_word_get_inflated_lock (lw)->hash_code = hash;
lw = lock_word_set_has_hash (lw);
mono_memory_write_barrier ();
obj->synchronisation = lw.sync;
return hash;
#else
/*
* Wang's address-based hash function:
* http://www.concentric.net/~Ttwang/tech/addrhash.htm
*/
return (GPOINTER_TO_UINT (obj) >> MONO_OBJECT_ALIGNMENT_SHIFT) * 2654435761u;
#endif
}
static void
mono_monitor_ensure_owned (LockWord lw, guint32 id)
{
if (lock_word_is_flat (lw)) {
if (lock_word_get_owner (lw) == id)
return;
} else if (lock_word_is_inflated (lw)) {
if (mon_status_get_owner (lock_word_get_inflated_lock (lw)->status) == id)
return;
}
mono_set_pending_exception (mono_get_exception_synchronization_lock ("Object synchronization method was called from an unsynchronized block of code."));
}
/*
* When this function is called it has already been established that the
* current thread owns the monitor.
*/
static void
mono_monitor_exit_inflated (MonoObject *obj)
{
LockWord lw;
MonoThreadsSync *mon;
guint32 nest;
lw.sync = obj->synchronisation;
mon = lock_word_get_inflated_lock (lw);
nest = mon->nest - 1;
if (nest == 0) {
guint32 new_status, old_status, tmp_status;
old_status = mon->status;
/*
* Release lock and do the wakeup stuff. It's possible that
* the last blocking thread gave up waiting just before we
* release the semaphore resulting in a negative entry count
* and a futile wakeup next time there's contention for this
* object.
*/
for (;;) {
gboolean have_waiters = mon_status_have_waiters (old_status);
new_status = mon_status_set_owner (old_status, 0);
if (have_waiters)
new_status = mon_status_decrement_entry_count (new_status);
tmp_status = InterlockedCompareExchange ((gint32*)&mon->status, new_status, old_status);
if (tmp_status == old_status) {
if (have_waiters)
ReleaseSemaphore (mon->entry_sem, 1, NULL);
break;
}
old_status = tmp_status;
}
LOCK_DEBUG (g_message ("%s: (%d) Object %p is now unlocked", __func__, mono_thread_info_get_small_id (), obj));
/* object is now unlocked, leave nest==1 so we don't
* need to set it when the lock is reacquired
*/
} else {
LOCK_DEBUG (g_message ("%s: (%d) Object %p is now locked %d times", __func__, mono_thread_info_get_small_id (), obj, nest));
mon->nest = nest;
}
}
/*
* When this function is called it has already been established that the
* current thread owns the monitor.
*/
static void
mono_monitor_exit_flat (MonoObject *obj, LockWord old_lw)
{
LockWord new_lw, tmp_lw;
if (G_UNLIKELY (lock_word_is_nested (old_lw)))
new_lw = lock_word_decrement_nest (old_lw);
else
new_lw.lock_word = 0;
tmp_lw.sync = (MonoThreadsSync *)InterlockedCompareExchangePointer ((gpointer*)&obj->synchronisation, new_lw.sync, old_lw.sync);
if (old_lw.sync != tmp_lw.sync) {
/* Someone inflated the lock in the meantime */
mono_monitor_exit_inflated (obj);
}
LOCK_DEBUG (g_message ("%s: (%d) Object %p is now locked %d times; LW = %p", __func__, mono_thread_info_get_small_id (), obj, lock_word_get_nest (new_lw), obj->synchronisation));
}
static void
mon_decrement_entry_count (MonoThreadsSync *mon)
{
guint32 old_status, tmp_status, new_status;
/* Decrement entry count */
old_status = mon->status;
for (;;) {
new_status = mon_status_decrement_entry_count (old_status);
tmp_status = InterlockedCompareExchange ((gint32*)&mon->status, new_status, old_status);
if (tmp_status == old_status) {
break;
}
old_status = tmp_status;
}
}
/* If allow_interruption==TRUE, the method will be interrumped if abort or suspend
* is requested. In this case it returns -1.
*/
static inline gint32
mono_monitor_try_enter_inflated (MonoObject *obj, guint32 ms, gboolean allow_interruption, guint32 id)
{
LockWord lw;
MonoThreadsSync *mon;
HANDLE sem;
gint64 then = 0, now, delta;
guint32 waitms;
guint32 ret;
guint32 new_status, old_status, tmp_status;
MonoInternalThread *thread;
gboolean interrupted = FALSE;
LOCK_DEBUG (g_message("%s: (%d) Trying to lock object %p (%d ms)", __func__, id, obj, ms));
if (G_UNLIKELY (!obj)) {
mono_set_pending_exception (mono_get_exception_argument_null ("obj"));
return FALSE;
}
lw.sync = obj->synchronisation;
mon = lock_word_get_inflated_lock (lw);
retry:
/* This case differs from Dice's case 3 because we don't
* deflate locks or cache unused lock records
*/
old_status = mon->status;
if (G_LIKELY (mon_status_get_owner (old_status) == 0)) {
/* Try to install our ID in the owner field, nest
* should have been left at 1 by the previous unlock
* operation
*/
new_status = mon_status_set_owner (old_status, id);
tmp_status = InterlockedCompareExchange ((gint32*)&mon->status, new_status, old_status);
if (G_LIKELY (tmp_status == old_status)) {
/* Success */
g_assert (mon->nest == 1);
return 1;
} else {
/* Trumped again! */
goto retry;
}
}
/* If the object is currently locked by this thread... */
if (mon_status_get_owner (old_status) == id) {
mon->nest++;
return 1;
}
/* The object must be locked by someone else... */
#ifndef DISABLE_PERFCOUNTERS
mono_perfcounters->thread_contentions++;
#endif
/* If ms is 0 we don't block, but just fail straight away */
if (ms == 0) {
LOCK_DEBUG (g_message ("%s: (%d) timed out, returning FALSE", __func__, id));
return 0;
}
mono_profiler_monitor_event (obj, MONO_PROFILER_MONITOR_CONTENTION);
/* The slow path begins here. */
retry_contended:
/* a small amount of duplicated code, but it allows us to insert the profiler
* callbacks without impacting the fast path: from here on we don't need to go back to the
* retry label, but to retry_contended. At this point mon is already installed in the object
* header.
*/
/* This case differs from Dice's case 3 because we don't
* deflate locks or cache unused lock records
*/
old_status = mon->status;
if (G_LIKELY (mon_status_get_owner (old_status) == 0)) {
/* Try to install our ID in the owner field, nest
* should have been left at 1 by the previous unlock
* operation
*/
new_status = mon_status_set_owner (old_status, id);
tmp_status = InterlockedCompareExchange ((gint32*)&mon->status, new_status, old_status);
if (G_LIKELY (tmp_status == old_status)) {
/* Success */
g_assert (mon->nest == 1);
mono_profiler_monitor_event (obj, MONO_PROFILER_MONITOR_DONE);
return 1;
}
}
/* If the object is currently locked by this thread... */
if (mon_status_get_owner (old_status) == id) {
mon->nest++;
mono_profiler_monitor_event (obj, MONO_PROFILER_MONITOR_DONE);
return 1;
}
/* We need to make sure there's a semaphore handle (creating it if
* necessary), and block on it
*/
if (mon->entry_sem == NULL) {
/* Create the semaphore */
sem = CreateSemaphore (NULL, 0, 0x7fffffff, NULL);
g_assert (sem != NULL);
if (InterlockedCompareExchangePointer ((gpointer*)&mon->entry_sem, sem, NULL) != NULL) {
/* Someone else just put a handle here */
CloseHandle (sem);
}
}
/*
* We need to register ourselves as waiting if it is the first time we are waiting,
* of if we were signaled and failed to acquire the lock.
*/
if (!interrupted) {
old_status = mon->status;
for (;;) {
if (mon_status_get_owner (old_status) == 0)
goto retry_contended;
new_status = mon_status_increment_entry_count (old_status);
tmp_status = InterlockedCompareExchange ((gint32*)&mon->status, new_status, old_status);
if (tmp_status == old_status) {
break;
}
old_status = tmp_status;
}
}
if (ms != INFINITE) {
then = mono_msec_ticks ();
}
waitms = ms;
#ifndef DISABLE_PERFCOUNTERS
mono_perfcounters->thread_queue_len++;
mono_perfcounters->thread_queue_max++;
#endif
thread = mono_thread_internal_current ();
mono_thread_set_state (thread, ThreadState_WaitSleepJoin);
/*
* We pass TRUE instead of allow_interruption since we have to check for the
* StopRequested case below.
*/
MONO_ENTER_GC_SAFE;
ret = WaitForSingleObjectEx (mon->entry_sem, waitms, TRUE);
MONO_EXIT_GC_SAFE;
mono_thread_clr_state (thread, ThreadState_WaitSleepJoin);
#ifndef DISABLE_PERFCOUNTERS
mono_perfcounters->thread_queue_len--;
#endif
if (ret == WAIT_IO_COMPLETION && !allow_interruption) {
interrupted = TRUE;
/*
* We have to obey a stop/suspend request even if
* allow_interruption is FALSE to avoid hangs at shutdown.
*/
if (!mono_thread_test_state (mono_thread_internal_current (), (MonoThreadState)(ThreadState_StopRequested | ThreadState_SuspendRequested | ThreadState_AbortRequested))) {
if (ms != INFINITE) {
now = mono_msec_ticks ();
/* it should not overflow before ~30k years */
g_assert (now >= then);
delta = now - then;
if (delta >= ms) {
ms = 0;
} else {
ms -= delta;
}
}
/* retry from the top */
goto retry_contended;
}
} else if (ret == WAIT_OBJECT_0) {
interrupted = FALSE;
/* retry from the top */
goto retry_contended;
} else if (ret == WAIT_TIMEOUT) {
/* we're done */
}
/* Timed out or interrupted */
mon_decrement_entry_count (mon);
mono_profiler_monitor_event (obj, MONO_PROFILER_MONITOR_FAIL);
if (ret == WAIT_IO_COMPLETION) {
LOCK_DEBUG (g_message ("%s: (%d) interrupted waiting, returning -1", __func__, id));
return -1;
} else if (ret == WAIT_TIMEOUT) {
LOCK_DEBUG (g_message ("%s: (%d) timed out waiting, returning FALSE", __func__, id));
return 0;
} else {
g_assert_not_reached ();
return 0;
}
}
/*
* If allow_interruption == TRUE, the method will be interrupted if abort or suspend
* is requested. In this case it returns -1.
*/
static inline gint32
mono_monitor_try_enter_internal (MonoObject *obj, guint32 ms, gboolean allow_interruption)
{
LockWord lw;
int id = mono_thread_info_get_small_id ();
LOCK_DEBUG (g_message("%s: (%d) Trying to lock object %p (%d ms)", __func__, id, obj, ms));
lw.sync = obj->synchronisation;
if (G_LIKELY (lock_word_is_free (lw))) {
LockWord nlw = lock_word_new_flat (id);
if (InterlockedCompareExchangePointer ((gpointer*)&obj->synchronisation, nlw.sync, NULL) == NULL) {
return 1;
} else {
/* Someone acquired it in the meantime or put a hash */
mono_monitor_inflate (obj);
return mono_monitor_try_enter_inflated (obj, ms, allow_interruption, id);
}
} else if (lock_word_is_inflated (lw)) {
return mono_monitor_try_enter_inflated (obj, ms, allow_interruption, id);
} else if (lock_word_is_flat (lw)) {
if (lock_word_get_owner (lw) == id) {
if (lock_word_is_max_nest (lw)) {
mono_monitor_inflate_owned (obj, id);
return mono_monitor_try_enter_inflated (obj, ms, allow_interruption, id);
} else {
LockWord nlw, old_lw;
nlw = lock_word_increment_nest (lw);
old_lw.sync = (MonoThreadsSync *)InterlockedCompareExchangePointer ((gpointer*)&obj->synchronisation, nlw.sync, lw.sync);
if (old_lw.sync != lw.sync) {
/* Someone else inflated it in the meantime */
g_assert (lock_word_is_inflated (old_lw));
return mono_monitor_try_enter_inflated (obj, ms, allow_interruption, id);
}
return 1;
}
} else {
mono_monitor_inflate (obj);
return mono_monitor_try_enter_inflated (obj, ms, allow_interruption, id);
}
} else if (lock_word_has_hash (lw)) {
mono_monitor_inflate (obj);
return mono_monitor_try_enter_inflated (obj, ms, allow_interruption, id);
}
g_assert_not_reached ();
return -1;
}
gboolean
mono_monitor_enter (MonoObject *obj)
{
if (G_UNLIKELY (!obj)) {
mono_set_pending_exception (mono_get_exception_argument_null ("obj"));
return FALSE;
}
return mono_monitor_try_enter_internal (obj, INFINITE, FALSE) == 1;
}
gboolean
mono_monitor_enter_fast (MonoObject *obj)
{
if (G_UNLIKELY (!obj)) {
/* don't set pending exn on the fast path, just return
* FALSE and let the slow path take care of it. */
return FALSE;
}
return mono_monitor_try_enter_internal (obj, 0, FALSE) == 1;
}
gboolean
mono_monitor_try_enter (MonoObject *obj, guint32 ms)
{
if (G_UNLIKELY (!obj)) {
mono_set_pending_exception (mono_get_exception_argument_null ("obj"));
return FALSE;
}
return mono_monitor_try_enter_internal (obj, ms, FALSE) == 1;
}
void
mono_monitor_exit (MonoObject *obj)
{
LockWord lw;
LOCK_DEBUG (g_message ("%s: (%d) Unlocking %p", __func__, mono_thread_info_get_small_id (), obj));
if (G_UNLIKELY (!obj)) {
mono_set_pending_exception (mono_get_exception_argument_null ("obj"));
return;
}
lw.sync = obj->synchronisation;
mono_monitor_ensure_owned (lw, mono_thread_info_get_small_id ());
if (G_UNLIKELY (lock_word_is_inflated (lw)))
mono_monitor_exit_inflated (obj);
else
mono_monitor_exit_flat (obj, lw);
}
guint32
mono_monitor_get_object_monitor_gchandle (MonoObject *object)
{
LockWord lw;
lw.sync = object->synchronisation;
if (lock_word_is_inflated (lw)) {
MonoThreadsSync *mon = lock_word_get_inflated_lock (lw);
return (guint32)mon->data;
}
return 0;
}
/*
* mono_monitor_threads_sync_member_offset:
* @status_offset: returns size and offset of the "status" member
* @nest_offset: returns size and offset of the "nest" member
*
* Returns the offsets and sizes of two members of the
* MonoThreadsSync struct. The Monitor ASM fastpaths need this.
*/
void
mono_monitor_threads_sync_members_offset (int *status_offset, int *nest_offset)
{
MonoThreadsSync ts;
#define ENCODE_OFF_SIZE(o,s) (((o) << 8) | ((s) & 0xff))
*status_offset = ENCODE_OFF_SIZE (MONO_STRUCT_OFFSET (MonoThreadsSync, status), sizeof (ts.status));
*nest_offset = ENCODE_OFF_SIZE (MONO_STRUCT_OFFSET (MonoThreadsSync, nest), sizeof (ts.nest));
}
void
ves_icall_System_Threading_Monitor_Monitor_try_enter_with_atomic_var (MonoObject *obj, guint32 ms, char *lockTaken)
{
gint32 res;
if (G_UNLIKELY (!obj)) {
mono_set_pending_exception (mono_get_exception_argument_null ("obj"));
return;
}
do {
res = mono_monitor_try_enter_internal (obj, ms, TRUE);
/*This means we got interrupted during the wait and didn't got the monitor.*/
if (res == -1) {
MonoException *exc = mono_thread_interruption_checkpoint ();
if (exc) {
mono_set_pending_exception (exc);
return;
}
}
} while (res == -1);
/*It's safe to do it from here since interruption would happen only on the wrapper.*/
*lockTaken = res == 1;
}
void
mono_monitor_enter_v4 (MonoObject *obj, char *lock_taken)
{
if (*lock_taken == 1) {
mono_set_pending_exception (mono_get_exception_argument ("lockTaken", "lockTaken is already true"));
return;
}
ves_icall_System_Threading_Monitor_Monitor_try_enter_with_atomic_var (obj, INFINITE, lock_taken);
}
/*
* mono_monitor_enter_v4_fast:
*
* Same as mono_monitor_enter_v4, but return immediately if the
* monitor cannot be acquired.
* Returns TRUE if the lock was acquired, FALSE otherwise.
*/
gboolean
mono_monitor_enter_v4_fast (MonoObject *obj, char *lock_taken)
{
if (*lock_taken == 1)
return FALSE;
if (G_UNLIKELY (!obj))
return FALSE;
gint32 res = mono_monitor_try_enter_internal (obj, 0, TRUE);
*lock_taken = res == 1;
return res == 1;
}
gboolean
ves_icall_System_Threading_Monitor_Monitor_test_owner (MonoObject *obj)
{
LockWord lw;
LOCK_DEBUG (g_message ("%s: Testing if %p is owned by thread %d", __func__, obj, mono_thread_info_get_small_id()));
lw.sync = obj->synchronisation;
if (lock_word_is_flat (lw)) {
return lock_word_get_owner (lw) == mono_thread_info_get_small_id ();
} else if (lock_word_is_inflated (lw)) {
return mon_status_get_owner (lock_word_get_inflated_lock (lw)->status) == mono_thread_info_get_small_id ();
}
return(FALSE);
}
gboolean
ves_icall_System_Threading_Monitor_Monitor_test_synchronised (MonoObject *obj)
{
LockWord lw;
LOCK_DEBUG (g_message("%s: (%d) Testing if %p is owned by any thread", __func__, mono_thread_info_get_small_id (), obj));
lw.sync = obj->synchronisation;
if (lock_word_is_flat (lw)) {
return !lock_word_is_free (lw);
} else if (lock_word_is_inflated (lw)) {
return mon_status_get_owner (lock_word_get_inflated_lock (lw)->status) != 0;
}
return FALSE;
}
/* All wait list manipulation in the pulse, pulseall and wait
* functions happens while the monitor lock is held, so we don't need
* any extra struct locking
*/
void
ves_icall_System_Threading_Monitor_Monitor_pulse (MonoObject *obj)
{
int id;
LockWord lw;
MonoThreadsSync *mon;
LOCK_DEBUG (g_message ("%s: (%d) Pulsing %p", __func__, mono_thread_info_get_small_id (), obj));
id = mono_thread_info_get_small_id ();
lw.sync = obj->synchronisation;
mono_monitor_ensure_owned (lw, id);
if (!lock_word_is_inflated (lw)) {
/* No threads waiting. A wait would have inflated the lock */
return;
}
mon = lock_word_get_inflated_lock (lw);
LOCK_DEBUG (g_message ("%s: (%d) %d threads waiting", __func__, mono_thread_info_get_small_id (), g_slist_length (mon->wait_list)));
if (mon->wait_list != NULL) {
LOCK_DEBUG (g_message ("%s: (%d) signalling and dequeuing handle %p", __func__, mono_thread_info_get_small_id (), mon->wait_list->data));
SetEvent (mon->wait_list->data);
mon->wait_list = g_slist_remove (mon->wait_list, mon->wait_list->data);
}
}
void
ves_icall_System_Threading_Monitor_Monitor_pulse_all (MonoObject *obj)
{
int id;
LockWord lw;
MonoThreadsSync *mon;
LOCK_DEBUG (g_message("%s: (%d) Pulsing all %p", __func__, mono_thread_info_get_small_id (), obj));
id = mono_thread_info_get_small_id ();
lw.sync = obj->synchronisation;
mono_monitor_ensure_owned (lw, id);
if (!lock_word_is_inflated (lw)) {
/* No threads waiting. A wait would have inflated the lock */
return;
}
mon = lock_word_get_inflated_lock (lw);
LOCK_DEBUG (g_message ("%s: (%d) %d threads waiting", __func__, mono_thread_info_get_small_id (), g_slist_length (mon->wait_list)));
while (mon->wait_list != NULL) {
LOCK_DEBUG (g_message ("%s: (%d) signalling and dequeuing handle %p", __func__, mono_thread_info_get_small_id (), mon->wait_list->data));
SetEvent (mon->wait_list->data);
mon->wait_list = g_slist_remove (mon->wait_list, mon->wait_list->data);
}
}
gboolean
ves_icall_System_Threading_Monitor_Monitor_wait (MonoObject *obj, guint32 ms)
{
LockWord lw;
MonoThreadsSync *mon;
HANDLE event;
guint32 nest;
guint32 ret;
gboolean success = FALSE;
gint32 regain;
MonoInternalThread *thread = mono_thread_internal_current ();
int id = mono_thread_info_get_small_id ();
LOCK_DEBUG (g_message ("%s: (%d) Trying to wait for %p with timeout %dms", __func__, mono_thread_info_get_small_id (), obj, ms));
lw.sync = obj->synchronisation;
mono_monitor_ensure_owned (lw, id);
if (!lock_word_is_inflated (lw)) {
mono_monitor_inflate_owned (obj, id);
lw.sync = obj->synchronisation;
}
mon = lock_word_get_inflated_lock (lw);
/* Do this WaitSleepJoin check before creating the event handle */
if (mono_thread_current_check_pending_interrupt ())
return FALSE;
event = CreateEvent (NULL, FALSE, FALSE, NULL);
if (event == NULL) {
mono_set_pending_exception (mono_get_exception_synchronization_lock ("Failed to set up wait event"));
return FALSE;
}
LOCK_DEBUG (g_message ("%s: (%d) queuing handle %p", __func__, mono_thread_info_get_small_id (), event));
/* This looks superfluous */
if (mono_thread_current_check_pending_interrupt ()) {
CloseHandle (event);
return FALSE;
}
mono_thread_set_state (thread, ThreadState_WaitSleepJoin);
mon->wait_list = g_slist_append (mon->wait_list, event);
/* Save the nest count, and release the lock */
nest = mon->nest;
mon->nest = 1;
mono_memory_write_barrier ();
mono_monitor_exit_inflated (obj);
LOCK_DEBUG (g_message ("%s: (%d) Unlocked %p lock %p", __func__, mono_thread_info_get_small_id (), obj, mon));
/* There's no race between unlocking mon and waiting for the
* event, because auto reset events are sticky, and this event
* is private to this thread. Therefore even if the event was
* signalled before we wait, we still succeed.
*/
MONO_ENTER_GC_SAFE;
ret = WaitForSingleObjectEx (event, ms, TRUE);
MONO_EXIT_GC_SAFE;
/* Reset the thread state fairly early, so we don't have to worry
* about the monitor error checking
*/
mono_thread_clr_state (thread, ThreadState_WaitSleepJoin);
/* Regain the lock with the previous nest count */
do {
regain = mono_monitor_try_enter_inflated (obj, INFINITE, TRUE, id);
/* We must regain the lock before handling interruption requests */
} while (regain == -1);
g_assert (regain == 1);
mon->nest = nest;
LOCK_DEBUG (g_message ("%s: (%d) Regained %p lock %p", __func__, mono_thread_info_get_small_id (), obj, mon));
if (ret == WAIT_TIMEOUT) {
/* Poll the event again, just in case it was signalled
* while we were trying to regain the monitor lock
*/
MONO_ENTER_GC_SAFE;
ret = WaitForSingleObjectEx (event, 0, FALSE);
MONO_EXIT_GC_SAFE;
}
/* Pulse will have popped our event from the queue if it signalled
* us, so we only do it here if the wait timed out.
*
* This avoids a race condition where the thread holding the
* lock can Pulse several times before the WaitForSingleObject
* returns. If we popped the queue here then this event might
* be signalled more than once, thereby starving another
* thread.
*/
if (ret == WAIT_OBJECT_0) {
LOCK_DEBUG (g_message ("%s: (%d) Success", __func__, mono_thread_info_get_small_id ()));
success = TRUE;
} else {
LOCK_DEBUG (g_message ("%s: (%d) Wait failed, dequeuing handle %p", __func__, mono_thread_info_get_small_id (), event));
/* No pulse, so we have to remove ourself from the
* wait queue
*/
mon->wait_list = g_slist_remove (mon->wait_list, event);
}
CloseHandle (event);
return success;
}
Something went wrong with that request. Please try again.