mono/metadata/w32handle.c

/**
 * \file
 * Generic and internal operations on handles
 *
 * Author:
 *	Dick Porter (dick@ximian.com)
 *	Ludovic Henry (luhenry@microsoft.com)
 *
 * (C) 2002-2011 Novell, Inc.
 * Copyright 2011 Xamarin Inc
 * Licensed under the MIT license. See LICENSE file in the project root for full license information.
 */

#include <config.h>
#include <glib.h>

#include "w32handle.h"

#include "utils/atomic.h"
#include "utils/mono-logger-internals.h"
#include "utils/mono-proclib.h"
#include "utils/mono-threads.h"
#include "utils/mono-time.h"

#undef DEBUG_REFS

#define SLOT_MAX		(1024 * 32)

/* must be a power of 2 */
#define HANDLE_PER_SLOT	(256)

static MonoW32HandleCapability handle_caps [MONO_W32TYPE_COUNT];
static MonoW32HandleOps *handle_ops [MONO_W32TYPE_COUNT];

/*
 * We can hold SLOT_MAX * HANDLE_PER_SLOT handles.
 * If 4M handles are not enough... Oh, well... we will crash.
 */
#define SLOT_INDEX(x)	(x / HANDLE_PER_SLOT)
#define SLOT_OFFSET(x)	(x % HANDLE_PER_SLOT)

static MonoW32Handle **private_handles;
static guint32 private_handles_size = 0;

/*
 * This is an internal handle which is used for handling waiting for multiple handles.
 * Threads which wait for multiple handles wait on this one handle, and when a handle
 * is signalled, this handle is signalled too.
 */
static MonoCoopMutex global_signal_mutex;
static MonoCoopCond global_signal_cond;

static MonoCoopMutex scan_mutex;

static gboolean shutting_down = FALSE;

static const gchar*
mono_w32handle_ops_typename (MonoW32Type type);

const gchar*
mono_w32handle_get_typename (MonoW32Type type)
{
	return mono_w32handle_ops_typename (type);
}

void
mono_w32handle_set_signal_state (MonoW32Handle *handle_data, gboolean state, gboolean broadcast)
{
#ifdef DEBUG
	g_message ("%s: setting state of %p to %s (broadcast %s)", __func__,
		   handle, state?"TRUE":"FALSE", broadcast?"TRUE":"FALSE");
#endif

	if (state) {
		/* Tell everyone blocking on a single handle */

		/* The condition the global signal cond is waiting on is the signalling of
		 * _any_ handle. So lock it before setting the signalled state.
		 */
		mono_coop_mutex_lock (&global_signal_mutex);

		/* This function _must_ be called with
		 * handle->signal_mutex locked
		 */
		handle_data->signalled = TRUE;

		if (broadcast)
			mono_coop_cond_broadcast (&handle_data->signal_cond);
		else
			mono_coop_cond_signal (&handle_data->signal_cond);

		/* Tell everyone blocking on multiple handles that something
		 * was signalled
		 */
		mono_coop_cond_broadcast (&global_signal_cond);

		mono_coop_mutex_unlock (&global_signal_mutex);
	} else {
		handle_data->signalled = FALSE;
	}
}

gboolean
mono_w32handle_issignalled (MonoW32Handle *handle_data)
{
	return handle_data->signalled;
}

static void
mono_w32handle_set_in_use (MonoW32Handle *handle_data, gboolean in_use)
{
	handle_data->in_use = in_use;
}

static void
mono_w32handle_lock_signal_mutex (void)
{
#ifdef DEBUG
	g_message ("%s: lock global signal mutex", __func__);
#endif

	mono_coop_mutex_lock (&global_signal_mutex);
}

static void
mono_w32handle_unlock_signal_mutex (void)
{
#ifdef DEBUG
	g_message ("%s: unlock global signal mutex", __func__);
#endif

	mono_coop_mutex_unlock (&global_signal_mutex);
}

void
mono_w32handle_lock (MonoW32Handle *handle_data)
{
	mono_coop_mutex_lock (&handle_data->signal_mutex);
}

gboolean
mono_w32handle_trylock (MonoW32Handle *handle_data)
{
	return mono_coop_mutex_trylock (&handle_data->signal_mutex) == 0;
}

void
mono_w32handle_unlock (MonoW32Handle *handle_data)
{
	mono_coop_mutex_unlock (&handle_data->signal_mutex);
}

void
mono_w32handle_init (void)
{
	static gboolean initialized = FALSE;

	if (initialized)
		return;

	mono_coop_mutex_init (&scan_mutex);

	mono_coop_cond_init (&global_signal_cond);
	mono_coop_mutex_init (&global_signal_mutex);

	private_handles = g_new0 (MonoW32Handle*, SLOT_MAX);

	initialized = TRUE;
}

void
mono_w32handle_cleanup (void)
{
	int i;

	g_assert (!shutting_down);
	shutting_down = TRUE;

	for (i = 0; i < SLOT_MAX; ++i)
		g_free (private_handles [i]);

	g_free (private_handles);
}

static gsize
mono_w32handle_ops_typesize (MonoW32Type type);

/*
 * mono_w32handle_new_internal:
 * @type: Init handle to this type
 *
 * Search for a free handle and initialize it. Return the handle on
 * success and 0 on failure.  This is only called from
 * mono_w32handle_new, and scan_mutex must be held.
 */
static MonoW32Handle*
mono_w32handle_new_internal (MonoW32Type type, gpointer handle_specific)
{
	guint32 i, k, count;
	static guint32 last = 0;
	gboolean retry = FALSE;

	/* A linear scan should be fast enough.  Start from the last
	 * allocation, assuming that handles are allocated more often
	 * than they're freed. Leave the space reserved for file
	 * descriptors
	 */

	if (last == 0) {
		/* We need to go from 1 since a handle of value 0 can be considered invalid in managed code */
		last = 1;
	} else {
		retry = TRUE;
	}

again:
	count = last;
	for(i = SLOT_INDEX (count); i < private_handles_size; i++) {
		if (private_handles [i]) {
			for (k = SLOT_OFFSET (count); k < HANDLE_PER_SLOT; k++) {
				MonoW32Handle *handle_data = &private_handles [i][k];

				if (handle_data->type == MONO_W32TYPE_UNUSED) {
					last = count + 1;

					g_assert (handle_data->ref == 0);

					handle_data->type = type;
					handle_data->signalled = FALSE;
					handle_data->ref = 1;

					mono_coop_cond_init (&handle_data->signal_cond);
					mono_coop_mutex_init (&handle_data->signal_mutex);

					if (handle_specific)
						handle_data->specific = g_memdup (handle_specific, mono_w32handle_ops_typesize (type));

					return handle_data;
				}
				count++;
			}
		}
	}

	if (retry) {
		/* Try again from the beginning */
		last = 1;
		retry = FALSE;
		goto again;
	}

	/* Will need to expand the array.  The caller will sort it out */

	return GINT_TO_POINTER (-1);
}

gpointer
mono_w32handle_new (MonoW32Type type, gpointer handle_specific)
{
	MonoW32Handle *handle_data;

	g_assert (!shutting_down);

	mono_coop_mutex_lock (&scan_mutex);

	while ((handle_data = mono_w32handle_new_internal (type, handle_specific)) == GINT_TO_POINTER (-1)) {
		/* Try and expand the array, and have another go */
		if (private_handles_size >= SLOT_MAX) {
			mono_coop_mutex_unlock (&scan_mutex);

			/* We ran out of slots */
			mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: failed to create %s handle", __func__, mono_w32handle_ops_typename (type));
			return INVALID_HANDLE_VALUE;
		}

		private_handles [private_handles_size ++] = g_new0 (MonoW32Handle, HANDLE_PER_SLOT);
	}

	mono_coop_mutex_unlock (&scan_mutex);

	mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: create %s handle %p", __func__, mono_w32handle_ops_typename (type), handle_data);

	return (gpointer) handle_data;
}

static gboolean
mono_w32handle_ref_core (MonoW32Handle *handle_data);

static gboolean
mono_w32handle_unref_core (MonoW32Handle *handle_data);

static void
w32handle_destroy (MonoW32Handle *handle_data);

gpointer
mono_w32handle_duplicate (MonoW32Handle *handle_data)
{
	if (!mono_w32handle_ref_core (handle_data))
		g_error ("%s: unknown handle %p", __func__, handle_data);

	return (gpointer) handle_data;
}

gboolean
mono_w32handle_close (gpointer handle)
{
	MonoW32Handle *handle_data;
	gboolean destroy;

	if (handle == INVALID_HANDLE_VALUE)
		return FALSE;

	handle_data = (MonoW32Handle*) handle;

	if (handle_data->type == MONO_W32TYPE_UNUSED)
		return FALSE;

	destroy = mono_w32handle_unref_core (handle_data);
	if (destroy)
		w32handle_destroy (handle_data);

	return TRUE;
}

gboolean
mono_w32handle_lookup_and_ref (gpointer handle, MonoW32Handle **handle_data)
{
	g_assert (handle_data);

	if (handle == INVALID_HANDLE_VALUE)
		return FALSE;

	*handle_data = (MonoW32Handle*) handle;

	if (!mono_w32handle_ref_core (*handle_data))
		return FALSE;

	if ((*handle_data)->type == MONO_W32TYPE_UNUSED) {
		mono_w32handle_unref_core (*handle_data);
		return FALSE;
	}

	return TRUE;
}

void
mono_w32handle_foreach (gboolean (*on_each)(MonoW32Handle *handle_data, gpointer user_data), gpointer user_data)
{
	GPtrArray *handles_to_destroy;
	guint32 i, k;

	handles_to_destroy = NULL;

	mono_coop_mutex_lock (&scan_mutex);

	for (i = SLOT_INDEX (0); i < private_handles_size; i++) {
		if (!private_handles [i])
			continue;
		for (k = SLOT_OFFSET (0); k < HANDLE_PER_SLOT; k++) {
			MonoW32Handle *handle_data;
			gboolean destroy, finished;

			handle_data = &private_handles [i][k];
			if (handle_data->type == MONO_W32TYPE_UNUSED)
				continue;

			if (!mono_w32handle_ref_core (handle_data)) {
				/* we are racing with mono_w32handle_unref:
				 *  the handle ref has been decremented, but it
				 *  hasn't yet been destroyed. */
				continue;
			}

			finished = on_each (handle_data, user_data);

			/* we might have to destroy the handle here, as
			 * it could have been unrefed in another thread */
			destroy = mono_w32handle_unref_core (handle_data);
			if (destroy) {
				/* we do not destroy it while holding the scan_mutex
				 * lock, because w32handle_destroy also needs to take
				 * the lock, and it calls user code which might lead
				 * to a deadlock */
				if (!handles_to_destroy)
					handles_to_destroy = g_ptr_array_sized_new (4);
				g_ptr_array_add (handles_to_destroy, (gpointer) handle_data);
			}

			if (finished)
				goto done;
		}
	}

done:
	mono_coop_mutex_unlock (&scan_mutex);

	if (handles_to_destroy) {
		for (i = 0; i < handles_to_destroy->len; ++i)
			w32handle_destroy ((MonoW32Handle*) handles_to_destroy->pdata [i]);

		g_ptr_array_free (handles_to_destroy, TRUE);
	}
}

static gboolean
mono_w32handle_ref_core (MonoW32Handle *handle_data)
{
	guint old, new;

	do {
		old = handle_data->ref;
		if (old == 0)
			return FALSE;

		new = old + 1;
	} while (mono_atomic_cas_i32 ((gint32*) &handle_data->ref, (gint32)new, (gint32)old) != (gint32)old);

	mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: ref %s handle %p, ref: %d -> %d",
		__func__, mono_w32handle_ops_typename (handle_data->type), handle_data, old, new);

	return TRUE;
}

static gboolean
mono_w32handle_unref_core (MonoW32Handle *handle_data)
{
	MonoW32Type type;
	guint old, new;

	type = handle_data->type;

	do {
		old = handle_data->ref;
		if (!(old >= 1))
			g_error ("%s: handle %p has ref %d, it should be >= 1", __func__, handle_data, old);

		new = old - 1;
	} while (mono_atomic_cas_i32 ((gint32*) &handle_data->ref, (gint32)new, (gint32)old) != (gint32)old);

	/* handle_data might contain invalid data from now on, if
	 * another thread is unref'ing this handle at the same time */

	mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: unref %s handle %p, ref: %d -> %d destroy: %s",
		__func__, mono_w32handle_ops_typename (type), handle_data, old, new, new == 0 ? "true" : "false");

	return new == 0;
}

static void (*_wapi_handle_ops_get_close_func (MonoW32Type type))(gpointer, gpointer);

static void
w32handle_destroy (MonoW32Handle *handle_data)
{
	/* Need to copy the handle info, reset the slot in the
	 * array, and _only then_ call the close function to
	 * avoid race conditions (eg file descriptors being
	 * closed, and another file being opened getting the
	 * same fd racing the memset())
	 */
	MonoW32Type type;
	gpointer handle_specific;
	void (*close_func)(gpointer, gpointer);

	g_assert (!handle_data->in_use);

	type = handle_data->type;
	handle_specific = handle_data->specific;

	mono_coop_mutex_lock (&scan_mutex);

	mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: destroy %s handle %p", __func__, mono_w32handle_ops_typename (type), handle_data);

	mono_coop_mutex_destroy (&handle_data->signal_mutex);
	mono_coop_cond_destroy (&handle_data->signal_cond);

	memset (handle_data, 0, sizeof (MonoW32Handle));

	mono_coop_mutex_unlock (&scan_mutex);

	close_func = _wapi_handle_ops_get_close_func (type);
	if (close_func != NULL) {
		close_func (handle_data, handle_specific);
	}

	memset (handle_specific, 0, mono_w32handle_ops_typesize (type));

	g_free (handle_specific);
}

/* The handle must not be locked on entry to this function */
void
mono_w32handle_unref (MonoW32Handle *handle_data)
{
	gboolean destroy;

	destroy = mono_w32handle_unref_core (handle_data);
	if (destroy)
		w32handle_destroy (handle_data);
}

void
mono_w32handle_register_ops (MonoW32Type type, MonoW32HandleOps *ops)
{
	handle_ops [type] = ops;
}

void
mono_w32handle_register_capabilities (MonoW32Type type, MonoW32HandleCapability caps)
{
	handle_caps[type] = caps;
}

static gboolean
mono_w32handle_test_capabilities (MonoW32Handle *handle_data, MonoW32HandleCapability caps)
{
	mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: testing 0x%x against 0x%x (%d)", __func__,
		   handle_caps[handle_data->type], caps, handle_caps[handle_data->type] & caps);

	return (handle_caps [handle_data->type] & caps) != 0;
}

static void (*_wapi_handle_ops_get_close_func (MonoW32Type type))(gpointer, gpointer)
{
	if (handle_ops[type] != NULL &&
	    handle_ops[type]->close != NULL) {
		return (handle_ops[type]->close);
	}

	return (NULL);
}

static void
mono_w32handle_ops_details (MonoW32Handle *handle_data)
{
	if (handle_ops [handle_data->type] && handle_ops [handle_data->type]->details != NULL)
		handle_ops [handle_data->type]->details (handle_data);
}

static const gchar*
mono_w32handle_ops_typename (MonoW32Type type)
{
	g_assert (handle_ops [type]);
	g_assert (handle_ops [type]->typename);
	return handle_ops [type]->typename ();
}

static gsize
mono_w32handle_ops_typesize (MonoW32Type type)
{
	g_assert (handle_ops [type]);
	g_assert (handle_ops [type]->typesize);
	return handle_ops [type]->typesize ();
}

static void
mono_w32handle_ops_signal (MonoW32Handle *handle_data)
{
	if (handle_ops [handle_data->type] && handle_ops [handle_data->type]->signal)
		handle_ops [handle_data->type]->signal (handle_data);
}

static gboolean
mono_w32handle_ops_own (MonoW32Handle *handle_data, gboolean *abandoned)
{
	if (handle_ops [handle_data->type] && handle_ops [handle_data->type]->own_handle)
		return handle_ops [handle_data->type]->own_handle (handle_data, abandoned);

	return FALSE;
}

static gboolean
mono_w32handle_ops_isowned (MonoW32Handle *handle_data)
{
	if (handle_ops [handle_data->type] && handle_ops [handle_data->type]->is_owned)
		return handle_ops [handle_data->type]->is_owned (handle_data);

	return FALSE;
}

static MonoW32HandleWaitRet
mono_w32handle_ops_specialwait (MonoW32Handle *handle_data, guint32 timeout, gboolean *alerted)
{
	if (handle_ops [handle_data->type] && handle_ops [handle_data->type]->special_wait)
		return handle_ops [handle_data->type]->special_wait (handle_data, timeout, alerted);

	return MONO_W32HANDLE_WAIT_RET_FAILED;
}

static void
mono_w32handle_ops_prewait (MonoW32Handle *handle_data)
{
	if (handle_ops [handle_data->type] && handle_ops [handle_data->type]->prewait)
		handle_ops [handle_data->type]->prewait (handle_data);
}

static void
mono_w32handle_lock_handles (MonoW32Handle **handles_data, gsize nhandles)
{
	gint i, j, iter = 0;
#ifndef HOST_WIN32
	struct timespec sleepytime;
#endif

	/* Lock all the handles, with backoff */
again:
	for (i = 0; i < nhandles; i++) {
		if (!mono_w32handle_trylock (handles_data [i])) {
			/* Bummer */

			for (j = i - 1; j >= 0; j--)
				mono_w32handle_unlock (handles_data [j]);

			iter += 10;
			if (iter == 1000)
				iter = 10;

#ifdef HOST_WIN32
			SleepEx (iter, TRUE);
#else
			/* If iter ever reaches 1000 the nanosleep will
			 * return EINVAL immediately, but we have a
			 * design flaw if that happens. */
			g_assert (iter < 1000);

			sleepytime.tv_sec = 0;
			sleepytime.tv_nsec = iter * 1000000;
			nanosleep (&sleepytime, NULL);
#endif /* HOST_WIN32 */

			goto again;
		}
	}

	mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: Locked all handles", __func__);
}

static void
mono_w32handle_unlock_handles (MonoW32Handle **handles_data, gsize nhandles)
{
	gint i;

	for (i = nhandles - 1; i >= 0; i--)
		mono_w32handle_unlock (handles_data [i]);
}

static int
mono_w32handle_timedwait_signal_naked (MonoCoopCond *cond, MonoCoopMutex *mutex, guint32 timeout, gboolean poll, gboolean *alerted)
{
	int res;

	if (!poll) {
		res = mono_coop_cond_timedwait (cond, mutex, timeout);
	} else {
		/* This is needed when waiting for process handles */
		if (!alerted) {
			/*
			 * pthread_cond_(timed)wait() can return 0 even if the condition was not
			 * signalled.  This happens at least on Darwin.  We surface this, i.e., we
			 * get spurious wake-ups.
			 *
			 * http://pubs.opengroup.org/onlinepubs/007908775/xsh/pthread_cond_wait.html
			 */
			res = mono_coop_cond_timedwait (cond, mutex, timeout);
		} else {
			if (timeout < 100) {
				/* Real timeout is less than 100ms time */
				res = mono_coop_cond_timedwait (cond, mutex, timeout);
			} else {
				res = mono_coop_cond_timedwait (cond, mutex, 100);

				/* Mask the fake timeout, this will cause
				 * another poll if the cond was not really signaled
				 */
				if (res == -1)
					res = 0;
			}
		}
	}

	return res;
}

static void
signal_global (gpointer unused)
{
	/* If we reach here, then interrupt token is set to the flag value, which
	 * means that the target thread is either
	 * - before the first CAS in timedwait, which means it won't enter the wait.
	 * - it is after the first CAS, so it is already waiting, or it will enter
	 *    the wait, and it will be interrupted by the broadcast. */
	mono_coop_mutex_lock (&global_signal_mutex);
	mono_coop_cond_broadcast (&global_signal_cond);
	mono_coop_mutex_unlock (&global_signal_mutex);
}

static int
mono_w32handle_timedwait_signal (guint32 timeout, gboolean poll, gboolean *alerted)
{
	int res;

	mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: waiting for global", __func__);

	if (alerted)
		*alerted = FALSE;

	if (alerted) {
		mono_thread_info_install_interrupt (signal_global, NULL, alerted);
		if (*alerted)
			return 0;
	}

	res = mono_w32handle_timedwait_signal_naked (&global_signal_cond, &global_signal_mutex, timeout, poll, alerted);

	if (alerted)
		mono_thread_info_uninstall_interrupt (alerted);

	return res;
}

static void
signal_handle_and_unref (gpointer handle_duplicate)
{
	MonoW32Handle *handle_data;
	MonoCoopCond *cond;
	MonoCoopMutex *mutex;

	if (!mono_w32handle_lookup_and_ref (handle_duplicate, &handle_data))
		g_error ("%s: unknown handle %p", __func__, handle_duplicate);

	/* If we reach here, then interrupt token is set to the flag value, which
	 * means that the target thread is either
	 * - before the first CAS in timedwait, which means it won't enter the wait.
	 * - it is after the first CAS, so it is already waiting, or it will enter
	 *    the wait, and it will be interrupted by the broadcast. */
	cond = &handle_data->signal_cond;
	mutex = &handle_data->signal_mutex;

	mono_coop_mutex_lock (mutex);
	mono_coop_cond_broadcast (cond);
	mono_coop_mutex_unlock (mutex);

	mono_w32handle_unref (handle_data);

	mono_w32handle_close (handle_duplicate);
}

static int
mono_w32handle_timedwait_signal_handle (MonoW32Handle *handle_data, guint32 timeout, gboolean poll, gboolean *alerted)
{
	gpointer handle_duplicate;
	int res;

	mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: waiting for %p (type %s)", __func__, handle_data,
		   mono_w32handle_ops_typename (handle_data->type));

	if (alerted)
		*alerted = FALSE;

	if (alerted) {
		mono_thread_info_install_interrupt (signal_handle_and_unref, handle_duplicate = mono_w32handle_duplicate (handle_data), alerted);
		if (*alerted) {
			mono_w32handle_close (handle_duplicate);
			return 0;
		}
	}

	res = mono_w32handle_timedwait_signal_naked (&handle_data->signal_cond, &handle_data->signal_mutex, timeout, poll, alerted);

	if (alerted) {
		mono_thread_info_uninstall_interrupt (alerted);
		if (!*alerted) {
			/* if it is alerted, then the handle_duplicate is closed in the interrupt callback */
			mono_w32handle_close (handle_duplicate);
		}
	}

	return res;
}

static gboolean
dump_callback (MonoW32Handle *handle_data, gpointer user_data)
{
	g_print ("%p [%7s] signalled: %5s ref: %3d ",
		handle_data, mono_w32handle_ops_typename (handle_data->type), handle_data->signalled ? "true" : "false", handle_data->ref - 1 /* foreach increase ref by 1 */);
	mono_w32handle_ops_details (handle_data);
	g_print ("\n");

	return FALSE;
}

void mono_w32handle_dump (void)
{
	mono_w32handle_foreach (dump_callback, NULL);
}

static gboolean
own_if_signalled (MonoW32Handle *handle_data, gboolean *abandoned)
{
	if (!mono_w32handle_issignalled (handle_data))
		return FALSE;

	*abandoned = FALSE;
	mono_w32handle_ops_own (handle_data, abandoned);
	return TRUE;
}

static gboolean
own_if_owned (MonoW32Handle *handle_data, gboolean *abandoned)
{
	if (!mono_w32handle_ops_isowned (handle_data))
		return FALSE;

	*abandoned = FALSE;
	mono_w32handle_ops_own (handle_data, abandoned);
	return TRUE;
}

MonoW32HandleWaitRet
mono_w32handle_wait_one (gpointer handle, guint32 timeout, gboolean alertable)
{
	MonoW32Handle *handle_data;
	MonoW32HandleWaitRet ret;
	gboolean alerted;
	gint64 start;
	gboolean abandoned = FALSE;

	alerted = FALSE;

	if (!mono_w32handle_lookup_and_ref (handle, &handle_data))
		return MONO_W32HANDLE_WAIT_RET_FAILED;

	if (mono_w32handle_test_capabilities (handle_data, MONO_W32HANDLE_CAP_SPECIAL_WAIT)) {
		mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: handle %p has special wait", __func__, handle_data);

		mono_w32handle_unref (handle_data);
		return mono_w32handle_ops_specialwait (handle_data, timeout, alertable ? &alerted : NULL);
	}

	if (!mono_w32handle_test_capabilities (handle_data, MONO_W32HANDLE_CAP_WAIT)) {
		mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: handle %p can't be waited for", __func__, handle_data);

		mono_w32handle_unref (handle_data);
		return MONO_W32HANDLE_WAIT_RET_FAILED;
	}

	mono_w32handle_lock (handle_data);

	if (mono_w32handle_test_capabilities (handle_data, MONO_W32HANDLE_CAP_OWN)) {
		if (own_if_owned (handle_data, &abandoned)) {
			mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: handle %p already owned", __func__, handle_data);

			ret = abandoned ? MONO_W32HANDLE_WAIT_RET_ABANDONED_0 : MONO_W32HANDLE_WAIT_RET_SUCCESS_0;
			goto done;
		}
	}

	if (timeout != MONO_INFINITE_WAIT)
		start = mono_msec_ticks ();

	mono_w32handle_set_in_use (handle_data, TRUE);

	for (;;) {
		gint waited;

		if (own_if_signalled (handle_data, &abandoned)) {
			mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: handle %p signalled", __func__, handle_data);

			ret = abandoned ? MONO_W32HANDLE_WAIT_RET_ABANDONED_0 : MONO_W32HANDLE_WAIT_RET_SUCCESS_0;
			goto done;
		}

		mono_w32handle_ops_prewait (handle_data);

		if (timeout == MONO_INFINITE_WAIT) {
			waited = mono_w32handle_timedwait_signal_handle (handle_data, MONO_INFINITE_WAIT, FALSE, alertable ? &alerted : NULL);
		} else {
			gint64 elapsed;

			elapsed = mono_msec_ticks () - start;
			if (elapsed > timeout) {
				ret = MONO_W32HANDLE_WAIT_RET_TIMEOUT;
				goto done;
			}

			waited = mono_w32handle_timedwait_signal_handle (handle_data, timeout - elapsed, FALSE, alertable ? &alerted : NULL);
		}

		if (alerted) {
			ret = MONO_W32HANDLE_WAIT_RET_ALERTED;
			goto done;
		}

		if (waited != 0) {
			ret = MONO_W32HANDLE_WAIT_RET_TIMEOUT;
			goto done;
		}
	}

done:
	mono_w32handle_set_in_use (handle_data, FALSE);

	mono_w32handle_unlock (handle_data);

	mono_w32handle_unref (handle_data);

	return ret;
}

MonoW32HandleWaitRet
mono_w32handle_wait_multiple (gpointer *handles, gsize nhandles, gboolean waitall, guint32 timeout, gboolean alertable)
{
	MonoW32HandleWaitRet ret;
	gboolean alerted, poll;
	gint i;
	gint64 start;
	MonoW32Handle *handles_data [MONO_W32HANDLE_MAXIMUM_WAIT_OBJECTS], *handles_data_sorted [MONO_W32HANDLE_MAXIMUM_WAIT_OBJECTS];
	gboolean abandoned [MONO_W32HANDLE_MAXIMUM_WAIT_OBJECTS] = {0};

	if (nhandles == 0)
		return MONO_W32HANDLE_WAIT_RET_FAILED;

	if (nhandles == 1)
		return mono_w32handle_wait_one (handles [0], timeout, alertable);

	alerted = FALSE;

	if (nhandles > MONO_W32HANDLE_MAXIMUM_WAIT_OBJECTS) {
		mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: too many handles: %zd",
			__func__, nhandles);

		return MONO_W32HANDLE_WAIT_RET_FAILED;
	}

	for (i = 0; i < nhandles; ++i) {
		if (!mono_w32handle_lookup_and_ref (handles [i], &handles_data [i])) {
			for (; i >= 0; --i)
				mono_w32handle_unref (handles_data [i]);
			return MONO_W32HANDLE_WAIT_RET_FAILED;
		}
	}

	for (i = 0; i < nhandles; ++i) {
		if (!mono_w32handle_test_capabilities (handles_data[i], MONO_W32HANDLE_CAP_WAIT)
			 && !mono_w32handle_test_capabilities (handles_data[i], MONO_W32HANDLE_CAP_SPECIAL_WAIT))
		{
			mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: handle %p can't be waited for", __func__, handles_data [i]);

			for (i = nhandles - 1; i >= 0; --i)
				mono_w32handle_unref (handles_data [i]);

			return MONO_W32HANDLE_WAIT_RET_FAILED;
		}

		handles_data_sorted [i] = handles_data [i];
	}

	qsort (handles_data_sorted, nhandles, sizeof (gpointer), g_direct_equal);
	for (i = 1; i < nhandles; ++i) {
		if (handles_data_sorted [i - 1] == handles_data_sorted [i]) {
			mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: handle %p is duplicated", __func__, handles_data_sorted [i]);

			for (i = nhandles - 1; i >= 0; --i)
				mono_w32handle_unref (handles_data [i]);

			return MONO_W32HANDLE_WAIT_RET_FAILED;
		}
	}

	poll = FALSE;
	for (i = 0; i < nhandles; ++i) {
		if (handles_data [i]->type == MONO_W32TYPE_PROCESS) {
			/* Can't wait for a process handle + another handle without polling */
			poll = TRUE;
		}
	}

	if (timeout != MONO_INFINITE_WAIT)
		start = mono_msec_ticks ();

	for (;;) {
		gsize count, lowest;
		gboolean signalled;
		gint waited;

		count = 0;
		lowest = nhandles;

		mono_w32handle_lock_handles (handles_data, nhandles);

		for (i = 0; i < nhandles; i++) {
			if ((mono_w32handle_test_capabilities (handles_data [i], MONO_W32HANDLE_CAP_OWN) && mono_w32handle_ops_isowned (handles_data [i]))
				 || mono_w32handle_issignalled (handles_data [i]))
			{
				count ++;

				if (i < lowest)
					lowest = i;
			}
		}

		signalled = (waitall && count == nhandles) || (!waitall && count > 0);

		if (signalled) {
			for (i = 0; i < nhandles; i++) {
				if (own_if_signalled (handles_data [i], &abandoned [i]) && !waitall) {
					/* if we are calling WaitHandle.WaitAny, .NET only owns the first one; it matters for Mutex which
					 * throw AbandonedMutexException in case we owned it but didn't release it */
					break;
				}
			}
		}

		mono_w32handle_unlock_handles (handles_data, nhandles);

		if (signalled) {
			ret = MONO_W32HANDLE_WAIT_RET_SUCCESS_0 + lowest;
			for (i = lowest; i < nhandles; i++) {
				if (abandoned [i]) {
					ret = MONO_W32HANDLE_WAIT_RET_ABANDONED_0 + lowest;
					break;
				}
			}
			goto done;
		}

		for (i = 0; i < nhandles; i++) {
			mono_w32handle_ops_prewait (handles_data [i]);

			if (mono_w32handle_test_capabilities (handles_data [i], MONO_W32HANDLE_CAP_SPECIAL_WAIT)
				 && !mono_w32handle_issignalled (handles_data [i]))
			{
				mono_w32handle_ops_specialwait (handles_data [i], 0, alertable ? &alerted : NULL);
			}
		}

		mono_w32handle_lock_signal_mutex ();

		if (waitall) {
			signalled = TRUE;
			for (i = 0; i < nhandles; ++i) {
				if (!mono_w32handle_issignalled (handles_data [i])) {
					signalled = FALSE;
					break;
				}
			}
		} else {
			signalled = FALSE;
			for (i = 0; i < nhandles; ++i) {
				if (mono_w32handle_issignalled (handles_data [i])) {
					signalled = TRUE;
					break;
				}
			}
		}

		waited = 0;

		if (!signalled) {
			if (timeout == MONO_INFINITE_WAIT) {
				waited = mono_w32handle_timedwait_signal (MONO_INFINITE_WAIT, poll, alertable ? &alerted : NULL);
			} else {
				gint64 elapsed;

				elapsed = mono_msec_ticks () - start;
				if (elapsed > timeout) {
					ret = MONO_W32HANDLE_WAIT_RET_TIMEOUT;

					mono_w32handle_unlock_signal_mutex ();

					goto done;
				}

				waited = mono_w32handle_timedwait_signal (timeout - elapsed, poll, alertable ? &alerted : NULL);
			}
		}

		mono_w32handle_unlock_signal_mutex ();

		if (alerted) {
			ret = MONO_W32HANDLE_WAIT_RET_ALERTED;
			goto done;
		}

		if (waited != 0) {
			ret = MONO_W32HANDLE_WAIT_RET_TIMEOUT;
			goto done;
		}
	}

done:
	for (i = nhandles - 1; i >= 0; i--) {
		/* Unref everything we reffed above */
		mono_w32handle_unref (handles_data [i]);
	}

	return ret;
}

MonoW32HandleWaitRet
mono_w32handle_signal_and_wait (gpointer signal_handle, gpointer wait_handle, guint32 timeout, gboolean alertable)
{
	MonoW32Handle *signal_handle_data, *wait_handle_data, *handles_data [2];
	MonoW32HandleWaitRet ret;
	gint64 start;
	gboolean alerted;
	gboolean abandoned = FALSE;

	alerted = FALSE;

	if (!mono_w32handle_lookup_and_ref (signal_handle, &signal_handle_data)) {
		return MONO_W32HANDLE_WAIT_RET_FAILED;
	}
	if (!mono_w32handle_lookup_and_ref (wait_handle, &wait_handle_data)) {
		mono_w32handle_unref (signal_handle_data);
		return MONO_W32HANDLE_WAIT_RET_FAILED;
	}

	if (!mono_w32handle_test_capabilities (signal_handle_data, MONO_W32HANDLE_CAP_SIGNAL)) {
		mono_w32handle_unref (wait_handle_data);
		mono_w32handle_unref (signal_handle_data);
		return MONO_W32HANDLE_WAIT_RET_FAILED;
	}
	if (!mono_w32handle_test_capabilities (wait_handle_data, MONO_W32HANDLE_CAP_WAIT)) {
		mono_w32handle_unref (wait_handle_data);
		mono_w32handle_unref (signal_handle_data);
		return MONO_W32HANDLE_WAIT_RET_FAILED;
	}

	if (mono_w32handle_test_capabilities (wait_handle_data, MONO_W32HANDLE_CAP_SPECIAL_WAIT)) {
		g_warning ("%s: handle %p has special wait, implement me!!", __func__, wait_handle_data);
		mono_w32handle_unref (wait_handle_data);
		mono_w32handle_unref (signal_handle_data);
		return MONO_W32HANDLE_WAIT_RET_FAILED;
	}

	handles_data [0] = wait_handle_data;
	handles_data [1] = signal_handle_data;

	mono_w32handle_lock_handles (handles_data, 2);

	mono_w32handle_ops_signal (signal_handle_data);

	mono_w32handle_unlock (signal_handle_data);

	if (mono_w32handle_test_capabilities (wait_handle_data, MONO_W32HANDLE_CAP_OWN)) {
		if (own_if_owned (wait_handle_data, &abandoned)) {
			mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: handle %p already owned", __func__, wait_handle_data);

			ret = abandoned ? MONO_W32HANDLE_WAIT_RET_ABANDONED_0 : MONO_W32HANDLE_WAIT_RET_SUCCESS_0;
			goto done;
		}
	}

	if (timeout != MONO_INFINITE_WAIT)
		start = mono_msec_ticks ();

	for (;;) {
		gint waited;

		if (own_if_signalled (wait_handle_data, &abandoned)) {
			mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_IO_LAYER_HANDLE, "%s: handle %p signalled", __func__, wait_handle_data);

			ret = abandoned ? MONO_W32HANDLE_WAIT_RET_ABANDONED_0 : MONO_W32HANDLE_WAIT_RET_SUCCESS_0;
			goto done;
		}

		mono_w32handle_ops_prewait (wait_handle_data);

		if (timeout == MONO_INFINITE_WAIT) {
			waited = mono_w32handle_timedwait_signal_handle (wait_handle_data, MONO_INFINITE_WAIT, FALSE, alertable ? &alerted : NULL);
		} else {
			gint64 elapsed;

			elapsed = mono_msec_ticks () - start;
			if (elapsed > timeout) {
				ret = MONO_W32HANDLE_WAIT_RET_TIMEOUT;
				goto done;
			}

			waited = mono_w32handle_timedwait_signal_handle (wait_handle_data, timeout - elapsed, FALSE, alertable ? &alerted : NULL);
		}

		if (alerted) {
			ret = MONO_W32HANDLE_WAIT_RET_ALERTED;
			goto done;
		}

		if (waited != 0) {
			ret = MONO_W32HANDLE_WAIT_RET_TIMEOUT;
			goto done;
		}
	}

done:
	mono_w32handle_unlock (wait_handle_data);

	mono_w32handle_unref (wait_handle_data);
	mono_w32handle_unref (signal_handle_data);

	return ret;
}