gc.c

/*
 * metadata/gc.c: GC icalls.
 *
 * Author: Paolo Molaro <lupus@ximian.com>
 *
 * Copyright 2002-2003 Ximian, Inc (http://www.ximian.com)
 * Copyright 2004-2009 Novell, Inc (http://www.novell.com)
 * Copyright 2012 Xamarin Inc (http://www.xamarin.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/gc-internals.h>
#include <mono/metadata/mono-gc.h>
#include <mono/metadata/threads.h>
#include <mono/metadata/tabledefs.h>
#include <mono/metadata/exception.h>
#include <mono/metadata/profiler-private.h>
#include <mono/metadata/domain-internals.h>
#include <mono/metadata/class-internals.h>
#include <mono/metadata/metadata-internals.h>
#include <mono/metadata/mono-mlist.h>
#include <mono/metadata/threads-types.h>
#include <mono/metadata/threadpool-ms.h>
#include <mono/sgen/sgen-conf.h>
#include <mono/sgen/sgen-gc.h>
#include <mono/utils/mono-logger-internals.h>
#include <mono/metadata/gc-internals.h>
#include <mono/metadata/marshal.h> /* for mono_delegate_free_ftnptr () */
#include <mono/metadata/attach.h>
#include <mono/metadata/console-io.h>
#include <mono/utils/mono-os-semaphore.h>
#include <mono/utils/mono-memory-model.h>
#include <mono/utils/mono-counters.h>
#include <mono/utils/mono-time.h>
#include <mono/utils/dtrace.h>
#include <mono/utils/mono-threads.h>
#include <mono/utils/mono-threads-coop.h>
#include <mono/utils/atomic.h>
#include <mono/utils/mono-coop-semaphore.h>
#include <mono/utils/hazard-pointer.h>

#ifndef HOST_WIN32
#include <pthread.h>
#endif

typedef struct DomainFinalizationReq {
	gint32 ref;
	MonoDomain *domain;
	MonoCoopSem done;
} DomainFinalizationReq;

static gboolean gc_disabled;

static gboolean finalizing_root_domain;

gboolean log_finalizers;
gboolean mono_do_not_finalize;
volatile gboolean suspend_finalizers;
gchar **mono_do_not_finalize_class_names ;

#define mono_finalizer_lock() mono_coop_mutex_lock (&finalizer_mutex)
#define mono_finalizer_unlock() mono_coop_mutex_unlock (&finalizer_mutex)
static MonoCoopMutex finalizer_mutex;
static MonoCoopMutex reference_queue_mutex;

static GSList *domains_to_finalize;
static MonoMList *threads_to_finalize;

static gboolean finalizer_thread_exited;
/* Uses finalizer_mutex */
static MonoCoopCond exited_cond;

static MonoInternalThread *gc_thread;

#ifdef TARGET_WIN32
static HANDLE pending_done_event;
#else
static gboolean pending_done;
static MonoCoopCond pending_done_cond;
static MonoCoopMutex pending_done_mutex;
#endif

static void object_register_finalizer (MonoObject *obj, void (*callback)(void *, void*));

static void reference_queue_proccess_all (void);
static void mono_reference_queue_cleanup (void);
static void reference_queue_clear_for_domain (MonoDomain *domain);


static guint32
guarded_wait (HANDLE handle, guint32 timeout, gboolean alertable)
{
	guint32 result;

	MONO_ENTER_GC_SAFE;
	result = WaitForSingleObjectEx (handle, timeout, alertable);
	MONO_EXIT_GC_SAFE;

	return result;
}

typedef struct {
	MonoCoopCond *cond;
	MonoCoopMutex *mutex;
} BreakCoopAlertableWaitUD;

static inline void
break_coop_alertable_wait (gpointer user_data)
{
	BreakCoopAlertableWaitUD *ud = (BreakCoopAlertableWaitUD*)user_data;

	mono_coop_mutex_lock (ud->mutex);
	mono_coop_cond_signal (ud->cond);
	mono_coop_mutex_unlock (ud->mutex);

	g_free (ud);
}

/*
 * coop_cond_timedwait_alertable:
 *
 *   Wait on COND/MUTEX. If ALERTABLE is non-null, the wait can be interrupted.
 * In that case, *ALERTABLE will be set to TRUE, and 0 is returned.
 */
static inline gint
coop_cond_timedwait_alertable (MonoCoopCond *cond, MonoCoopMutex *mutex, guint32 timeout_ms, gboolean *alertable)
{
	BreakCoopAlertableWaitUD *ud;
	int res;

	if (alertable) {
		ud = g_new0 (BreakCoopAlertableWaitUD, 1);
		ud->cond = cond;
		ud->mutex = mutex;

		mono_thread_info_install_interrupt (break_coop_alertable_wait, ud, alertable);
		if (*alertable) {
			g_free (ud);
			return 0;
		}
	}
	res = mono_coop_cond_timedwait (cond, mutex, timeout_ms);
	if (alertable) {
		mono_thread_info_uninstall_interrupt (alertable);
		if (*alertable)
			return 0;
		else {
			/* the interrupt token has not been taken by another
			 * thread, so it's our responsability to free it up. */
			g_free (ud);
		}
	}
	return res;
}

static gboolean
add_thread_to_finalize (MonoInternalThread *thread, MonoError *error)
{
	mono_error_init (error);
	mono_finalizer_lock ();
	if (!threads_to_finalize)
		MONO_GC_REGISTER_ROOT_SINGLE (threads_to_finalize, MONO_ROOT_SOURCE_FINALIZER_QUEUE, "finalizable threads list");
	threads_to_finalize = mono_mlist_append_checked (threads_to_finalize, (MonoObject*)thread, error);
	mono_finalizer_unlock ();
	return is_ok (error);
}

/* 
 * actually, we might want to queue the finalize requests in a separate thread,
 * but we need to be careful about the execution domain of the thread...
 */
void
mono_gc_run_finalize (void *obj, void *data)
{
	MonoError error;
	MonoObject *exc = NULL;
	MonoObject *o;
#ifndef HAVE_SGEN_GC
	MonoObject *o2;
#endif
	MonoMethod* finalizer = NULL;
	MonoDomain *caller_domain = mono_domain_get ();
	MonoDomain *domain;
	RuntimeInvokeFunction runtime_invoke;

	// This function is called from the innards of the GC, so our best alternative for now is to do polling here
	mono_threads_safepoint ();

	o = (MonoObject*)((char*)obj + GPOINTER_TO_UINT (data));

	if (mono_do_not_finalize) {
		if (!mono_do_not_finalize_class_names)
			return;

		size_t namespace_len = strlen (o->vtable->klass->name_space);
		for (int i = 0; mono_do_not_finalize_class_names [i]; ++i) {
			const char *name = mono_do_not_finalize_class_names [i];
			if (strncmp (name, o->vtable->klass->name_space, namespace_len))
				break;
			if (name [namespace_len] != '.')
				break;
			if (strcmp (name + namespace_len + 1, o->vtable->klass->name))
				break;
			return;
		}
	}

	if (log_finalizers)
		g_log ("mono-gc-finalizers", G_LOG_LEVEL_DEBUG, "<%s at %p> Starting finalizer checks.", o->vtable->klass->name, o);

	if (suspend_finalizers)
		return;

	domain = o->vtable->domain;

#ifndef HAVE_SGEN_GC
	mono_domain_finalizers_lock (domain);

	o2 = (MonoObject *)g_hash_table_lookup (domain->finalizable_objects_hash, o);

	mono_domain_finalizers_unlock (domain);

	if (!o2)
		/* Already finalized somehow */
		return;
#endif

	/* make sure the finalizer is not called again if the object is resurrected */
	object_register_finalizer ((MonoObject *)obj, NULL);

	if (log_finalizers)
		g_log ("mono-gc-finalizers", G_LOG_LEVEL_MESSAGE, "<%s at %p> Registered finalizer as processed.", o->vtable->klass->name, o);

	if (o->vtable->klass == mono_defaults.internal_thread_class) {
		MonoInternalThread *t = (MonoInternalThread*)o;

		if (mono_gc_is_finalizer_internal_thread (t))
			/* Avoid finalizing ourselves */
			return;

		if (t->threadpool_thread && finalizing_root_domain) {
			/* Don't finalize threadpool threads when
			   shutting down - they're finalized when the
			   threadpool shuts down. */
			if (!add_thread_to_finalize (t, &error))
				goto unhandled_error;
			return;
		}
	}

	if (o->vtable->klass->image == mono_defaults.corlib && !strcmp (o->vtable->klass->name, "DynamicMethod") && finalizing_root_domain) {
		/*
		 * These can't be finalized during unloading/shutdown, since that would
		 * free the native code which can still be referenced by other
		 * finalizers.
		 * FIXME: This is not perfect, objects dying at the same time as 
		 * dynamic methods can still reference them even when !shutdown.
		 */
		return;
	}

	if (mono_runtime_get_no_exec ())
		return;

	/* speedup later... and use a timeout */
	/* g_print ("Finalize run on %p %s.%s\n", o, mono_object_class (o)->name_space, mono_object_class (o)->name); */

	/* Use _internal here, since this thread can enter a doomed appdomain */
	mono_domain_set_internal (mono_object_domain (o));

	/* delegates that have a native function pointer allocated are
	 * registered for finalization, but they don't have a Finalize
	 * method, because in most cases it's not needed and it's just a waste.
	 */
	if (o->vtable->klass->delegate) {
		MonoDelegate* del = (MonoDelegate*)o;
		if (del->delegate_trampoline)
			mono_delegate_free_ftnptr ((MonoDelegate*)o);
		mono_domain_set_internal (caller_domain);
		return;
	}

	finalizer = mono_class_get_finalizer (o->vtable->klass);

	/* If object has a CCW but has no finalizer, it was only
	 * registered for finalization in order to free the CCW.
	 * Else it needs the regular finalizer run.
	 * FIXME: what to do about ressurection and suppression
	 * of finalizer on object with CCW.
	 */
	if (mono_marshal_free_ccw (o) && !finalizer) {
		mono_domain_set_internal (caller_domain);
		return;
	}

	/* 
	 * To avoid the locking plus the other overhead of mono_runtime_invoke_checked (),
	 * create and precompile a wrapper which calls the finalize method using
	 * a CALLVIRT.
	 */
	if (log_finalizers)
		g_log ("mono-gc-finalizers", G_LOG_LEVEL_MESSAGE, "<%s at %p> Compiling finalizer.", o->vtable->klass->name, o);

	if (!domain->finalize_runtime_invoke) {
		MonoMethod *invoke = mono_marshal_get_runtime_invoke (mono_class_get_method_from_name_flags (mono_defaults.object_class, "Finalize", 0, 0), TRUE);

		domain->finalize_runtime_invoke = mono_compile_method_checked (invoke, &error);
		mono_error_assert_ok (&error); /* expect this not to fail */
	}

	runtime_invoke = (RuntimeInvokeFunction)domain->finalize_runtime_invoke;

	mono_runtime_class_init_full (o->vtable, &error);
	if (!is_ok (&error))
		goto unhandled_error;

	if (G_UNLIKELY (MONO_GC_FINALIZE_INVOKE_ENABLED ())) {
		MONO_GC_FINALIZE_INVOKE ((unsigned long)o, mono_object_get_size (o),
				o->vtable->klass->name_space, o->vtable->klass->name);
	}

	if (log_finalizers)
		g_log ("mono-gc-finalizers", G_LOG_LEVEL_MESSAGE, "<%s at %p> Calling finalizer.", o->vtable->klass->name, o);

	mono_profiler_gc_finalize_object_begin (o);

	runtime_invoke (o, NULL, &exc, NULL);

	mono_profiler_gc_finalize_object_end (o);

	if (log_finalizers)
		g_log ("mono-gc-finalizers", G_LOG_LEVEL_MESSAGE, "<%s at %p> Returned from finalizer.", o->vtable->klass->name, o);

unhandled_error:
	if (!is_ok (&error))
		exc = (MonoObject*)mono_error_convert_to_exception (&error);
	if (exc)
		mono_thread_internal_unhandled_exception (exc);

	mono_domain_set_internal (caller_domain);
}

void
mono_gc_finalize_threadpool_threads (void)
{
	while (threads_to_finalize) {
		MonoInternalThread *thread = (MonoInternalThread*) mono_mlist_get_data (threads_to_finalize);

		/* Force finalization of the thread. */
		thread->threadpool_thread = FALSE;
		mono_object_register_finalizer ((MonoObject*)thread);

		mono_gc_run_finalize (thread, NULL);

		threads_to_finalize = mono_mlist_next (threads_to_finalize);
	}
}

gpointer
mono_gc_out_of_memory (size_t size)
{
	/* 
	 * we could allocate at program startup some memory that we could release 
	 * back to the system at this point if we're really low on memory (ie, size is
	 * lower than the memory we set apart)
	 */
	mono_raise_exception (mono_domain_get ()->out_of_memory_ex);

	return NULL;
}

/*
 * Some of our objects may point to a different address than the address returned by GC_malloc()
 * (because of the GetHashCode hack), but we need to pass the real address to register_finalizer.
 * This also means that in the callback we need to adjust the pointer to get back the real
 * MonoObject*.
 * We also need to be consistent in the use of the GC_debug* variants of malloc and register_finalizer, 
 * since that, too, can cause the underlying pointer to be offset.
 */
static void
object_register_finalizer (MonoObject *obj, void (*callback)(void *, void*))
{
	MonoDomain *domain;

	g_assert (obj != NULL);

	domain = obj->vtable->domain;

#if HAVE_BOEHM_GC
	if (mono_domain_is_unloading (domain) && (callback != NULL))
		/*
		 * Can't register finalizers in a dying appdomain, since they
		 * could be invoked after the appdomain has been unloaded.
		 */
		return;

	mono_domain_finalizers_lock (domain);

	if (callback)
		g_hash_table_insert (domain->finalizable_objects_hash, obj, obj);
	else
		g_hash_table_remove (domain->finalizable_objects_hash, obj);

	mono_domain_finalizers_unlock (domain);

	mono_gc_register_for_finalization (obj, callback);
#elif defined(HAVE_SGEN_GC)
	/*
	 * If we register finalizers for domains that are unloading we might
	 * end up running them while or after the domain is being cleared, so
	 * the objects will not be valid anymore.
	 */
	if (!mono_domain_is_unloading (domain))
		mono_gc_register_for_finalization (obj, callback);
#endif
}

/**
 * mono_object_register_finalizer:
 * @obj: object to register
 *
 * Records that object @obj has a finalizer, this will call the
 * Finalize method when the garbage collector disposes the object.
 * 
 */
void
mono_object_register_finalizer (MonoObject *obj)
{
	/* g_print ("Registered finalizer on %p %s.%s\n", obj, mono_object_class (obj)->name_space, mono_object_class (obj)->name); */
	object_register_finalizer (obj, mono_gc_run_finalize);
}

/**
 * mono_domain_finalize:
 * @domain: the domain to finalize
 * @timeout: msects to wait for the finalization to complete, -1 to wait indefinitely
 *
 *  Request finalization of all finalizable objects inside @domain. Wait
 * @timeout msecs for the finalization to complete.
 *
 * Returns: TRUE if succeeded, FALSE if there was a timeout
 */

gboolean
mono_domain_finalize (MonoDomain *domain, guint32 timeout) 
{
	DomainFinalizationReq *req;
	MonoInternalThread *thread = mono_thread_internal_current ();
	gint res;
	gboolean ret;
	gint64 start;

#if defined(__native_client__)
	return FALSE;
#endif

	if (mono_thread_internal_current () == gc_thread)
		/* We are called from inside a finalizer, not much we can do here */
		return FALSE;

	/* 
	 * No need to create another thread 'cause the finalizer thread
	 * is still working and will take care of running the finalizers
	 */ 
	
	if (gc_disabled)
		return TRUE;

	/* We don't support domain finalization without a GC */
	if (mono_gc_is_null ())
		return FALSE;

	mono_gc_collect (mono_gc_max_generation ());

	req = g_new0 (DomainFinalizationReq, 1);
	req->ref = 2;
	req->domain = domain;
	mono_coop_sem_init (&req->done, 0);

	if (domain == mono_get_root_domain ())
		finalizing_root_domain = TRUE;
	
	mono_finalizer_lock ();

	domains_to_finalize = g_slist_append (domains_to_finalize, req);

	mono_finalizer_unlock ();

	/* Tell the finalizer thread to finalize this appdomain */
	mono_gc_finalize_notify ();

	if (timeout == -1)
		timeout = INFINITE;
	if (timeout != INFINITE)
		start = mono_msec_ticks ();

	ret = TRUE;

	for (;;) {
		if (timeout == INFINITE) {
			res = mono_coop_sem_wait (&req->done, MONO_SEM_FLAGS_ALERTABLE);
		} else {
			gint64 elapsed = mono_msec_ticks () - start;
			if (elapsed >= timeout) {
				ret = FALSE;
				break;
			}

			res = mono_coop_sem_timedwait (&req->done, timeout - elapsed, MONO_SEM_FLAGS_ALERTABLE);
		}

		if (res == MONO_SEM_TIMEDWAIT_RET_SUCCESS) {
			break;
		} else if (res == MONO_SEM_TIMEDWAIT_RET_ALERTED) {
			if ((thread->state & (ThreadState_StopRequested | ThreadState_SuspendRequested)) != 0) {
				ret = FALSE;
				break;
			}
		} else if (res == MONO_SEM_TIMEDWAIT_RET_TIMEDOUT) {
			ret = FALSE;
			break;
		} else {
			g_error ("%s: unknown result %d", __func__, res);
		}
	}

	if (!ret) {
		/* Try removing the req from domains_to_finalize:
		 *  - if it's not found: the domain is being finalized,
		 *     so we the ref count is already decremented
		 *  - if it's found: the domain is not yet being finalized,
		 *     so we can safely decrement the ref */

		gboolean found;

		mono_finalizer_lock ();

		found = g_slist_index (domains_to_finalize, req) != -1;
		if (found)
			domains_to_finalize = g_slist_remove (domains_to_finalize, req);

		mono_finalizer_unlock ();

		if (found) {
			/* We have to decrement it wherever we
			 * remove it from domains_to_finalize */
			if (InterlockedDecrement (&req->ref) != 1)
				g_error ("%s: req->ref should be 1, as we are the first one to decrement it", __func__);
		}

		goto done;
	}

	if (domain == mono_get_root_domain ()) {
		mono_threadpool_ms_cleanup ();
		mono_gc_finalize_threadpool_threads ();
	}

done:
	if (InterlockedDecrement (&req->ref) == 0) {
		mono_coop_sem_destroy (&req->done);
		g_free (req);
	}

	return ret;
}

void
ves_icall_System_GC_InternalCollect (int generation)
{
	mono_gc_collect (generation);
}

gint64
ves_icall_System_GC_GetTotalMemory (MonoBoolean forceCollection)
{
	if (forceCollection)
		mono_gc_collect (mono_gc_max_generation ());
	return mono_gc_get_used_size ();
}

void
ves_icall_System_GC_KeepAlive (MonoObject *obj)
{
	/*
	 * Does nothing.
	 */
}

void
ves_icall_System_GC_ReRegisterForFinalize (MonoObject *obj)
{
	MONO_CHECK_ARG_NULL (obj,);

	object_register_finalizer (obj, mono_gc_run_finalize);
}

void
ves_icall_System_GC_SuppressFinalize (MonoObject *obj)
{
	MONO_CHECK_ARG_NULL (obj,);

	/* delegates have no finalizers, but we register them to deal with the
	 * unmanaged->managed trampoline. We don't let the user suppress it
	 * otherwise we'd leak it.
	 */
	if (obj->vtable->klass->delegate)
		return;

	/* FIXME: Need to handle case where obj has COM Callable Wrapper
	 * generated for it that needs cleaned up, but user wants to suppress
	 * their derived object finalizer. */

	object_register_finalizer (obj, NULL);
}

void
ves_icall_System_GC_WaitForPendingFinalizers (void)
{
	if (mono_gc_is_null ())
		return;

	if (!mono_gc_pending_finalizers ())
		return;

	if (mono_thread_internal_current () == gc_thread)
		/* Avoid deadlocks */
		return;

	/*
	If the finalizer thread is not live, lets pretend no finalizers are pending since the current thread might
	be the one responsible for starting it up.
	*/
	if (gc_thread == NULL)
		return;

#ifdef TARGET_WIN32
	ResetEvent (pending_done_event);
	mono_gc_finalize_notify ();
	/* g_print ("Waiting for pending finalizers....\n"); */
	guarded_wait (pending_done_event, INFINITE, TRUE);
	/* g_print ("Done pending....\n"); */
#else
	gboolean alerted = FALSE;
	mono_coop_mutex_lock (&pending_done_mutex);
	pending_done = FALSE;
	mono_gc_finalize_notify ();
	while (!pending_done) {
		coop_cond_timedwait_alertable (&pending_done_cond, &pending_done_mutex, INFINITE, &alerted);
		if (alerted)
			break;
	}
	mono_coop_mutex_unlock (&pending_done_mutex);
#endif
}

void
ves_icall_System_GC_register_ephemeron_array (MonoObject *array)
{
#ifdef HAVE_SGEN_GC
	if (!mono_gc_ephemeron_array_add (array)) {
		mono_set_pending_exception (mono_object_domain (array)->out_of_memory_ex);
		return;
	}
#endif
}

MonoObject*
ves_icall_System_GC_get_ephemeron_tombstone (void)
{
	return mono_domain_get ()->ephemeron_tombstone;
}

MonoObject *
ves_icall_System_GCHandle_GetTarget (guint32 handle)
{
	return mono_gchandle_get_target (handle);
}

/*
 * if type == -1, change the target of the handle, otherwise allocate a new handle.
 */
guint32
ves_icall_System_GCHandle_GetTargetHandle (MonoObject *obj, guint32 handle, gint32 type)
{
	if (type == -1) {
		mono_gchandle_set_target (handle, obj);
		/* the handle doesn't change */
		return handle;
	}
	switch (type) {
	case HANDLE_WEAK:
		return mono_gchandle_new_weakref (obj, FALSE);
	case HANDLE_WEAK_TRACK:
		return mono_gchandle_new_weakref (obj, TRUE);
	case HANDLE_NORMAL:
		return mono_gchandle_new (obj, FALSE);
	case HANDLE_PINNED:
		return mono_gchandle_new (obj, TRUE);
	default:
		g_assert_not_reached ();
	}
	return 0;
}

void
ves_icall_System_GCHandle_FreeHandle (guint32 handle)
{
	mono_gchandle_free (handle);
}

gpointer
ves_icall_System_GCHandle_GetAddrOfPinnedObject (guint32 handle)
{
	MonoObject *obj;

	if (MONO_GC_HANDLE_TYPE (handle) != HANDLE_PINNED)
		return (gpointer)-2;
	obj = mono_gchandle_get_target (handle);
	if (obj) {
		MonoClass *klass = mono_object_class (obj);
		if (klass == mono_defaults.string_class) {
			return mono_string_chars ((MonoString*)obj);
		} else if (klass->rank) {
			return mono_array_addr ((MonoArray*)obj, char, 0);
		} else {
			/* the C# code will check and throw the exception */
			/* FIXME: missing !klass->blittable test, see bug #61134 */
			if ((klass->flags & TYPE_ATTRIBUTE_LAYOUT_MASK) == TYPE_ATTRIBUTE_AUTO_LAYOUT)
				return (gpointer)-1;
			return (char*)obj + sizeof (MonoObject);
		}
	}
	return NULL;
}

MonoBoolean
mono_gc_GCHandle_CheckCurrentDomain (guint32 gchandle)
{
	return mono_gchandle_is_in_domain (gchandle, mono_domain_get ());
}

static MonoCoopSem finalizer_sem;
static volatile gboolean finished;

/*
 * mono_gc_finalize_notify:
 *
 *   Notify the finalizer thread that finalizers etc.
 * are available to be processed.
 */
void
mono_gc_finalize_notify (void)
{
#ifdef DEBUG
	g_message ( "%s: prodding finalizer", __func__);
#endif

	if (mono_gc_is_null ())
		return;

	mono_coop_sem_post (&finalizer_sem);
}

/*
This is the number of entries allowed in the hazard free queue before
we explicitly cycle the finalizer thread to trigger pumping the queue.

It was picked empirically by running the corlib test suite in a stress
scenario where all hazard entries are queued.

In this extreme scenario we double the number of times we cycle the finalizer
thread compared to just GC calls.

Entries are usually in the order of 100's of bytes each, so we're limiting
floating garbage to be in the order of a dozen kb.
*/
static gboolean finalizer_thread_pulsed;
#define HAZARD_QUEUE_OVERFLOW_SIZE 20

static void
hazard_free_queue_is_too_big (size_t size)
{
	if (size < HAZARD_QUEUE_OVERFLOW_SIZE)
		return;

	if (finalizer_thread_pulsed || InterlockedCompareExchange (&finalizer_thread_pulsed, TRUE, FALSE))
		return;

	mono_gc_finalize_notify ();
}

static void
hazard_free_queue_pump (void)
{
	mono_thread_hazardous_try_free_all ();
	finalizer_thread_pulsed = FALSE;
}

#ifdef HAVE_BOEHM_GC

static void
collect_objects (gpointer key, gpointer value, gpointer user_data)
{
	GPtrArray *arr = (GPtrArray*)user_data;
	g_ptr_array_add (arr, key);
}

#endif

/*
 * finalize_domain_objects:
 *
 *  Run the finalizers of all finalizable objects in req->domain.
 */
static void
finalize_domain_objects (void)
{
	DomainFinalizationReq *req = NULL;
	MonoDomain *domain;

	if (domains_to_finalize) {
		mono_finalizer_lock ();
		if (domains_to_finalize) {
			req = (DomainFinalizationReq *)domains_to_finalize->data;
			domains_to_finalize = g_slist_remove (domains_to_finalize, req);
		}
		mono_finalizer_unlock ();
	}

	if (!req)
		return;

	domain = req->domain;

	/* Process finalizers which are already in the queue */
	mono_gc_invoke_finalizers ();

#ifdef HAVE_BOEHM_GC
	while (g_hash_table_size (domain->finalizable_objects_hash) > 0) {
		int i;
		GPtrArray *objs;
		/* 
		 * Since the domain is unloading, nobody is allowed to put
		 * new entries into the hash table. But finalize_object might
		 * remove entries from the hash table, so we make a copy.
		 */
		objs = g_ptr_array_new ();
		g_hash_table_foreach (domain->finalizable_objects_hash, collect_objects, objs);
		/* printf ("FINALIZING %d OBJECTS.\n", objs->len); */

		for (i = 0; i < objs->len; ++i) {
			MonoObject *o = (MonoObject*)g_ptr_array_index (objs, i);
			/* FIXME: Avoid finalizing threads, etc */
			mono_gc_run_finalize (o, 0);
		}

		g_ptr_array_free (objs, TRUE);
	}
#elif defined(HAVE_SGEN_GC)
	mono_gc_finalize_domain (domain);
	mono_gc_invoke_finalizers ();
#endif

	/* cleanup the reference queue */
	reference_queue_clear_for_domain (domain);
	
	/* printf ("DONE.\n"); */
	mono_coop_sem_post (&req->done);

	if (InterlockedDecrement (&req->ref) == 0) {
		/* mono_domain_finalize already returned, and
		 * doesn't hold a reference to req anymore. */
		mono_coop_sem_destroy (&req->done);
		g_free (req);
	}
}

static guint32
finalizer_thread (gpointer unused)
{
	MonoError error;
	gboolean wait = TRUE;

	mono_thread_set_name_internal (mono_thread_internal_current (), mono_string_new (mono_get_root_domain (), "Finalizer"), FALSE, &error);
	mono_error_assert_ok (&error);

	/* Register a hazard free queue pump callback */
	mono_hazard_pointer_install_free_queue_size_callback (hazard_free_queue_is_too_big);

	while (!finished) {
		/* Wait to be notified that there's at least one
		 * finaliser to run
		 */

		g_assert (mono_domain_get () == mono_get_root_domain ());
		mono_gc_set_skip_thread (TRUE);

		if (wait) {
			/* An alertable wait is required so this thread can be suspended on windows */
			mono_coop_sem_wait (&finalizer_sem, MONO_SEM_FLAGS_ALERTABLE);
		}
		wait = TRUE;

		mono_gc_set_skip_thread (FALSE);

		mono_threads_perform_thread_dump ();

		mono_console_handle_async_ops ();

		mono_attach_maybe_start ();

		finalize_domain_objects ();

		mono_profiler_gc_finalize_begin ();

		/* If finished == TRUE, mono_gc_cleanup has been called (from mono_runtime_cleanup),
		 * before the domain is unloaded.
		 */
		mono_gc_invoke_finalizers ();

		mono_profiler_gc_finalize_end ();

		mono_threads_join_threads ();

		reference_queue_proccess_all ();

		hazard_free_queue_pump ();

		/* Avoid posting the pending done event until there are pending finalizers */
		if (mono_coop_sem_timedwait (&finalizer_sem, 0, MONO_SEM_FLAGS_NONE) == MONO_SEM_TIMEDWAIT_RET_SUCCESS) {
			/* Don't wait again at the start of the loop */
			wait = FALSE;
		} else {
#ifdef TARGET_WIN32
			SetEvent (pending_done_event);
#else
			mono_coop_mutex_lock (&pending_done_mutex);
			pending_done = TRUE;
			mono_coop_cond_signal (&pending_done_cond);
			mono_coop_mutex_unlock (&pending_done_mutex);
#endif
		}
	}

	mono_finalizer_lock ();
	finalizer_thread_exited = TRUE;
	mono_coop_cond_signal (&exited_cond);
	mono_finalizer_unlock ();

	return 0;
}

#ifndef LAZY_GC_THREAD_CREATION
static
#endif
void
mono_gc_init_finalizer_thread (void)
{
	MonoError error;
	gc_thread = mono_thread_create_internal (mono_domain_get (), finalizer_thread, NULL, FALSE, 0, &error);
	mono_error_assert_ok (&error);
}

void
mono_gc_init (void)
{
	mono_coop_mutex_init_recursive (&finalizer_mutex);
	mono_coop_mutex_init_recursive (&reference_queue_mutex);

	mono_counters_register ("Minor GC collections", MONO_COUNTER_GC | MONO_COUNTER_UINT, &gc_stats.minor_gc_count);
	mono_counters_register ("Major GC collections", MONO_COUNTER_GC | MONO_COUNTER_UINT, &gc_stats.major_gc_count);
	mono_counters_register ("Minor GC time", MONO_COUNTER_GC | MONO_COUNTER_ULONG | MONO_COUNTER_TIME, &gc_stats.minor_gc_time);
	mono_counters_register ("Major GC time", MONO_COUNTER_GC | MONO_COUNTER_ULONG | MONO_COUNTER_TIME, &gc_stats.major_gc_time);
	mono_counters_register ("Major GC time concurrent", MONO_COUNTER_GC | MONO_COUNTER_ULONG | MONO_COUNTER_TIME, &gc_stats.major_gc_time_concurrent);

	mono_gc_base_init ();

	if (mono_gc_is_disabled ()) {
		gc_disabled = TRUE;
		return;
	}

#ifdef TARGET_WIN32
	pending_done_event = CreateEvent (NULL, TRUE, FALSE, NULL);
	g_assert (pending_done_event);
#else
	mono_coop_cond_init (&pending_done_cond);
	mono_coop_mutex_init (&pending_done_mutex);
#endif

	mono_coop_cond_init (&exited_cond);
	mono_coop_sem_init (&finalizer_sem, 0);

#ifndef LAZY_GC_THREAD_CREATION
	mono_gc_init_finalizer_thread ();
#endif
}

void
mono_gc_cleanup (void)
{
#ifdef DEBUG
	g_message ("%s: cleaning up finalizer", __func__);
#endif

	if (mono_gc_is_null ())
		return;

	if (!gc_disabled) {
		finished = TRUE;
		if (mono_thread_internal_current () != gc_thread) {
			gint64 start_ticks = mono_msec_ticks ();
			gint64 end_ticks = start_ticks + 2000;

			mono_gc_finalize_notify ();
			/* Finishing the finalizer thread, so wait a little bit... */
			/* MS seems to wait for about 2 seconds */
			while (!finalizer_thread_exited) {
				gint64 current_ticks = mono_msec_ticks ();
				guint32 timeout;

				if (current_ticks >= end_ticks)
					break;
				else
					timeout = end_ticks - current_ticks;
				mono_finalizer_lock ();
				if (!finalizer_thread_exited)
					mono_coop_cond_timedwait (&exited_cond, &finalizer_mutex, timeout);
				mono_finalizer_unlock ();
			}

			if (!finalizer_thread_exited) {
				int ret;

				/* Set a flag which the finalizer thread can check */
				suspend_finalizers = TRUE;
				mono_gc_suspend_finalizers ();

				/* Try to abort the thread, in the hope that it is running managed code */
				mono_thread_internal_abort (gc_thread);

				/* Wait for it to stop */
				ret = guarded_wait (gc_thread->handle, 100, TRUE);

				if (ret == WAIT_TIMEOUT) {
					/*
					 * The finalizer thread refused to exit. Make it stop.
					 */
					mono_thread_internal_stop (gc_thread);
					ret = guarded_wait (gc_thread->handle, 100, TRUE);
					g_assert (ret != WAIT_TIMEOUT);
					/* The thread can't set this flag */
					finalizer_thread_exited = TRUE;
				}
			}

			int ret;

			/* Wait for the thread to actually exit */
			ret = guarded_wait (gc_thread->handle, INFINITE, TRUE);
			g_assert (ret == WAIT_OBJECT_0);

			mono_thread_join (GUINT_TO_POINTER (gc_thread->tid));
			g_assert (finalizer_thread_exited);
		}
		gc_thread = NULL;
		mono_gc_base_cleanup ();
	}

	mono_reference_queue_cleanup ();

	mono_coop_mutex_destroy (&finalizer_mutex);
	mono_coop_mutex_destroy (&reference_queue_mutex);
}

gboolean
mono_gc_is_finalizer_internal_thread (MonoInternalThread *thread)
{
	return thread == gc_thread;
}

/**
 * mono_gc_is_finalizer_thread:
 * @thread: the thread to test.
 *
 * In Mono objects are finalized asynchronously on a separate thread.
 * This routine tests whether the @thread argument represents the
 * finalization thread.
 * 
 * Returns: TRUE if @thread is the finalization thread.
 */
gboolean
mono_gc_is_finalizer_thread (MonoThread *thread)
{
	return mono_gc_is_finalizer_internal_thread (thread->internal_thread);
}

#if defined(__MACH__)
static pthread_t mach_exception_thread;

void
mono_gc_register_mach_exception_thread (pthread_t thread)
{
	mach_exception_thread = thread;
}

pthread_t
mono_gc_get_mach_exception_thread (void)
{
	return mach_exception_thread;
}
#endif

static MonoReferenceQueue *ref_queues;

static void
ref_list_remove_element (RefQueueEntry **prev, RefQueueEntry *element)
{
	do {
		/* Guard if head is changed concurrently. */
		while (*prev != element)
			prev = &(*prev)->next;
	} while (prev && InterlockedCompareExchangePointer ((volatile gpointer *)prev, element->next, element) != element);
}

static void
ref_list_push (RefQueueEntry **head, RefQueueEntry *value)
{
	RefQueueEntry *current;
	do {
		current = *head;
		value->next = current;
		STORE_STORE_FENCE; /*Must make sure the previous store is visible before the CAS. */
	} while (InterlockedCompareExchangePointer ((volatile gpointer *)head, value, current) != current);
}

static void
reference_queue_proccess (MonoReferenceQueue *queue)
{
	RefQueueEntry **iter = &queue->queue;
	RefQueueEntry *entry;
	while ((entry = *iter)) {
		if (queue->should_be_deleted || !mono_gchandle_get_target (entry->gchandle)) {
			mono_gchandle_free ((guint32)entry->gchandle);
			ref_list_remove_element (iter, entry);
			queue->callback (entry->user_data);
			g_free (entry);
		} else {
			iter = &entry->next;
		}
	}
}

static void
reference_queue_proccess_all (void)
{
	MonoReferenceQueue **iter;
	MonoReferenceQueue *queue = ref_queues;
	for (; queue; queue = queue->next)
		reference_queue_proccess (queue);

restart:
	mono_coop_mutex_lock (&reference_queue_mutex);
	for (iter = &ref_queues; *iter;) {
		queue = *iter;
		if (!queue->should_be_deleted) {
			iter = &queue->next;
			continue;
		}
		if (queue->queue) {
			mono_coop_mutex_unlock (&reference_queue_mutex);
			reference_queue_proccess (queue);
			goto restart;
		}
		*iter = queue->next;
		g_free (queue);
	}
	mono_coop_mutex_unlock (&reference_queue_mutex);
}

static void
mono_reference_queue_cleanup (void)
{
	MonoReferenceQueue *queue = ref_queues;
	for (; queue; queue = queue->next)
		queue->should_be_deleted = TRUE;
	reference_queue_proccess_all ();
}

static void
reference_queue_clear_for_domain (MonoDomain *domain)
{
	MonoReferenceQueue *queue = ref_queues;
	for (; queue; queue = queue->next) {
		RefQueueEntry **iter = &queue->queue;
		RefQueueEntry *entry;
		while ((entry = *iter)) {
			if (entry->domain == domain) {
				mono_gchandle_free ((guint32)entry->gchandle);
				ref_list_remove_element (iter, entry);
				queue->callback (entry->user_data);
				g_free (entry);
			} else {
				iter = &entry->next;
			}
		}
	}
}
/**
 * mono_gc_reference_queue_new:
 * @callback callback used when processing collected entries.
 *
 * Create a new reference queue used to process collected objects.
 * A reference queue let you add a pair of (managed object, user data)
 * using the mono_gc_reference_queue_add method.
 *
 * Once the managed object is collected @callback will be called
 * in the finalizer thread with 'user data' as argument.
 *
 * The callback is called from the finalizer thread without any locks held.
 * When a AppDomain is unloaded, all callbacks for objects belonging to it
 * will be invoked.
 *
 * @returns the new queue.
 */
MonoReferenceQueue*
mono_gc_reference_queue_new (mono_reference_queue_callback callback)
{
	MonoReferenceQueue *res = g_new0 (MonoReferenceQueue, 1);
	res->callback = callback;

	mono_coop_mutex_lock (&reference_queue_mutex);
	res->next = ref_queues;
	ref_queues = res;
	mono_coop_mutex_unlock (&reference_queue_mutex);

	return res;
}

/**
 * mono_gc_reference_queue_add:
 * @queue the queue to add the reference to.
 * @obj the object to be watched for collection
 * @user_data parameter to be passed to the queue callback
 *
 * Queue an object to be watched for collection, when the @obj is
 * collected, the callback that was registered for the @queue will
 * be invoked with @user_data as argument.
 *
 * @returns false if the queue is scheduled to be freed.
 */
gboolean
mono_gc_reference_queue_add (MonoReferenceQueue *queue, MonoObject *obj, void *user_data)
{
	RefQueueEntry *entry;
	if (queue->should_be_deleted)
		return FALSE;

	g_assert (obj != NULL);

	entry = g_new0 (RefQueueEntry, 1);
	entry->user_data = user_data;
	entry->domain = mono_object_domain (obj);

	entry->gchandle = mono_gchandle_new_weakref (obj, TRUE);
	mono_object_register_finalizer (obj);

	ref_list_push (&queue->queue, entry);
	return TRUE;
}

/**
 * mono_gc_reference_queue_free:
 * @queue the queue that should be freed.
 *
 * This operation signals that @queue should be freed. This operation is deferred
 * as it happens on the finalizer thread.
 *
 * After this call, no further objects can be queued. It's the responsibility of the
 * caller to make sure that no further attempt to access queue will be made.
 */
void
mono_gc_reference_queue_free (MonoReferenceQueue *queue)
{
	queue->should_be_deleted = TRUE;
}