lib/thread/thread.c

/*-
 *   BSD LICENSE
 *
 *   Copyright (c) Intel Corporation.
 *   All rights reserved.
 *
 *   Redistribution and use in source and binary forms, with or without
 *   modification, are permitted provided that the following conditions
 *   are met:
 *
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in
 *       the documentation and/or other materials provided with the
 *       distribution.
 *     * Neither the name of Intel Corporation nor the names of its
 *       contributors may be used to endorse or promote products derived
 *       from this software without specific prior written permission.
 *
 *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 *   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 *   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 *   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 *   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 *   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 *   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 *   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 *   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 *   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 *   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "spdk/stdinc.h"

#include "spdk/env.h"
#include "spdk/queue.h"
#include "spdk/string.h"
#include "spdk/thread.h"
#include "spdk/util.h"

#include "spdk_internal/log.h"
#include "spdk_internal/thread.h"

#ifdef __linux__
#include <sys/prctl.h>
#endif

#ifdef __FreeBSD__
#include <pthread_np.h>
#endif

#define SPDK_MSG_BATCH_SIZE		8

static pthread_mutex_t g_devlist_mutex = PTHREAD_MUTEX_INITIALIZER;

struct io_device {
	void				*io_device;
	char				*name;
	spdk_io_channel_create_cb	create_cb;
	spdk_io_channel_destroy_cb	destroy_cb;
	spdk_io_device_unregister_cb	unregister_cb;
	struct spdk_thread		*unregister_thread;
	uint32_t			ctx_size;
	uint32_t			for_each_count;
	TAILQ_ENTRY(io_device)		tailq;

	uint32_t			refcnt;

	bool				unregistered;
};

static TAILQ_HEAD(, io_device) g_io_devices = TAILQ_HEAD_INITIALIZER(g_io_devices);

struct spdk_msg {
	spdk_msg_fn		fn;
	void			*arg;
};

static struct spdk_mempool *g_spdk_msg_mempool = NULL;

enum spdk_poller_state {
	/* The poller is registered with a thread but not currently executing its fn. */
	SPDK_POLLER_STATE_WAITING,

	/* The poller is currently running its fn. */
	SPDK_POLLER_STATE_RUNNING,

	/* The poller was unregistered during the execution of its fn. */
	SPDK_POLLER_STATE_UNREGISTERED,
};

struct spdk_poller {
	TAILQ_ENTRY(spdk_poller)	tailq;

	/* Current state of the poller; should only be accessed from the poller's thread. */
	enum spdk_poller_state		state;

	uint64_t			period_ticks;
	uint64_t			next_run_tick;
	spdk_poller_fn			fn;
	void				*arg;
};

struct spdk_thread {
	pthread_t			thread_id;
	spdk_thread_pass_msg		msg_fn;
	spdk_start_poller		start_poller_fn;
	spdk_stop_poller		stop_poller_fn;
	void				*thread_ctx;
	TAILQ_HEAD(, spdk_io_channel)	io_channels;
	TAILQ_ENTRY(spdk_thread)	tailq;
	char				*name;

	/*
	 * Contains pollers actively running on this thread.  Pollers
	 *  are run round-robin. The thread takes one poller from the head
	 *  of the ring, executes it, then puts it back at the tail of
	 *  the ring.
	 */
	TAILQ_HEAD(, spdk_poller)	active_pollers;

	/**
	 * Contains pollers running on this thread with a periodic timer.
	 */
	TAILQ_HEAD(timer_pollers_head, spdk_poller) timer_pollers;

	struct spdk_ring		*messages;
};

static TAILQ_HEAD(, spdk_thread) g_threads = TAILQ_HEAD_INITIALIZER(g_threads);
static uint32_t g_thread_count = 0;

static __thread struct spdk_thread *tls_thread = NULL;

static inline struct spdk_thread *
_get_thread(void)
{
	return tls_thread;
}

static void
_set_thread_name(const char *thread_name)
{
#if defined(__linux__)
	prctl(PR_SET_NAME, thread_name, 0, 0, 0);
#elif defined(__FreeBSD__)
	pthread_set_name_np(pthread_self(), thread_name);
#else
#error missing platform support for thread name
#endif
}

int
spdk_thread_lib_init(void)
{
	char mempool_name[SPDK_MAX_MEMZONE_NAME_LEN];

	snprintf(mempool_name, sizeof(mempool_name), "msgpool_%d", getpid());
	g_spdk_msg_mempool = spdk_mempool_create(mempool_name,
			     262144 - 1, /* Power of 2 minus 1 is optimal for memory consumption */
			     sizeof(struct spdk_msg),
			     SPDK_MEMPOOL_DEFAULT_CACHE_SIZE,
			     SPDK_ENV_SOCKET_ID_ANY);

	if (!g_spdk_msg_mempool) {
		return -1;
	}

	return 0;
}

void
spdk_thread_lib_fini(void)
{
	struct io_device *dev;

	TAILQ_FOREACH(dev, &g_io_devices, tailq) {
		SPDK_ERRLOG("io_device %s not unregistered\n", dev->name);
	}

	if (g_spdk_msg_mempool) {
		spdk_mempool_free(g_spdk_msg_mempool);
	}
}

struct spdk_thread *
spdk_allocate_thread(spdk_thread_pass_msg msg_fn,
		     spdk_start_poller start_poller_fn,
		     spdk_stop_poller stop_poller_fn,
		     void *thread_ctx, const char *name)
{
	struct spdk_thread *thread;

	thread = _get_thread();
	if (thread) {
		SPDK_ERRLOG("Double allocated SPDK thread\n");
		return NULL;
	}

	if ((start_poller_fn != NULL && stop_poller_fn == NULL) ||
	    (start_poller_fn == NULL && stop_poller_fn != NULL)) {
		SPDK_ERRLOG("start_poller_fn and stop_poller_fn must either both be NULL or both be non-NULL\n");
		return NULL;
	}

	thread = calloc(1, sizeof(*thread));
	if (!thread) {
		SPDK_ERRLOG("Unable to allocate memory for thread\n");
		return NULL;
	}

	thread->thread_id = pthread_self();
	thread->msg_fn = msg_fn;
	thread->start_poller_fn = start_poller_fn;
	thread->stop_poller_fn = stop_poller_fn;
	thread->thread_ctx = thread_ctx;
	TAILQ_INIT(&thread->io_channels);
	TAILQ_INIT(&thread->active_pollers);
	TAILQ_INIT(&thread->timer_pollers);

	thread->messages = spdk_ring_create(SPDK_RING_TYPE_MP_SC, 65536, SPDK_ENV_SOCKET_ID_ANY);
	if (!thread->messages) {
		SPDK_ERRLOG("Unable to allocate memory for message ring\n");
		free(thread);
		return NULL;
	}

	if (name) {
		_set_thread_name(name);
		thread->name = strdup(name);
	} else {
		thread->name = spdk_sprintf_alloc("%p", thread);
	}

	SPDK_DEBUGLOG(SPDK_LOG_THREAD, "Allocating new thread %s\n", thread->name);

	pthread_mutex_lock(&g_devlist_mutex);
	TAILQ_INSERT_TAIL(&g_threads, thread, tailq);
	g_thread_count++;
	pthread_mutex_unlock(&g_devlist_mutex);

	return thread;
}

void
spdk_set_thread(struct spdk_thread *thread)
{
	tls_thread = thread;
}

void
spdk_free_thread(void)
{
	struct spdk_thread *thread;
	struct spdk_io_channel *ch;

	thread = _get_thread();
	if (!thread) {
		SPDK_ERRLOG("No thread allocated\n");
		return;
	}

	SPDK_DEBUGLOG(SPDK_LOG_THREAD, "Freeing thread %s\n", thread->name);

	TAILQ_FOREACH(ch, &thread->io_channels, tailq) {
		SPDK_ERRLOG("thread %s still has channel for io_device %s\n",
			    thread->name, ch->dev->name);
	}

	pthread_mutex_lock(&g_devlist_mutex);
	assert(g_thread_count > 0);
	g_thread_count--;
	TAILQ_REMOVE(&g_threads, thread, tailq);
	pthread_mutex_unlock(&g_devlist_mutex);

	free(thread->name);

	if (thread->messages) {
		spdk_ring_free(thread->messages);
	}

	free(thread);

	tls_thread = NULL;
}

static inline uint32_t
_spdk_msg_queue_run_batch(struct spdk_thread *thread, uint32_t max_msgs)
{
	unsigned count, i;
	void *messages[SPDK_MSG_BATCH_SIZE];

#ifdef DEBUG
	/*
	 * spdk_ring_dequeue() fills messages and returns how many entries it wrote,
	 * so we will never actually read uninitialized data from events, but just to be sure
	 * (and to silence a static analyzer false positive), initialize the array to NULL pointers.
	 */
	memset(messages, 0, sizeof(messages));
#endif

	if (max_msgs > 0) {
		max_msgs = spdk_min(max_msgs, SPDK_MSG_BATCH_SIZE);
	} else {
		max_msgs = SPDK_MSG_BATCH_SIZE;
	}

	count = spdk_ring_dequeue(thread->messages, messages, max_msgs);
	if (count == 0) {
		return 0;
	}

	for (i = 0; i < count; i++) {
		struct spdk_msg *msg = messages[i];

		assert(msg != NULL);
		msg->fn(msg->arg);
	}

	spdk_mempool_put_bulk(g_spdk_msg_mempool, messages, count);

	return count;
}

static void
_spdk_poller_insert_timer(struct spdk_thread *thread, struct spdk_poller *poller, uint64_t now)
{
	struct spdk_poller *iter;

	poller->next_run_tick = now + poller->period_ticks;

	/*
	 * Insert poller in the thread's timer_pollers list in sorted order by next scheduled
	 * run time.
	 */
	TAILQ_FOREACH_REVERSE(iter, &thread->timer_pollers, timer_pollers_head, tailq) {
		if (iter->next_run_tick <= poller->next_run_tick) {
			TAILQ_INSERT_AFTER(&thread->timer_pollers, iter, poller, tailq);
			return;
		}
	}

	/* No earlier pollers were found, so this poller must be the new head */
	TAILQ_INSERT_HEAD(&thread->timer_pollers, poller, tailq);
}

int
spdk_thread_poll(struct spdk_thread *thread, uint32_t max_msgs)
{
	uint32_t msg_count;
	struct spdk_poller *poller;
	int rc = 0;

	assert(_get_thread() == NULL);

	tls_thread = thread;

	msg_count = _spdk_msg_queue_run_batch(thread, max_msgs);
	if (msg_count) {
		rc = 1;
	}

	poller = TAILQ_FIRST(&thread->active_pollers);
	if (poller) {
		int poller_rc;

		TAILQ_REMOVE(&thread->active_pollers, poller, tailq);
		poller->state = SPDK_POLLER_STATE_RUNNING;
		poller_rc = poller->fn(poller->arg);
		if (poller->state == SPDK_POLLER_STATE_UNREGISTERED) {
			free(poller);
		} else {
			poller->state = SPDK_POLLER_STATE_WAITING;
			TAILQ_INSERT_TAIL(&thread->active_pollers, poller, tailq);
		}

#ifdef DEBUG
		if (poller_rc == -1) {
			SPDK_DEBUGLOG(SPDK_LOG_THREAD, "Poller %p returned -1\n", poller);
		}
#endif

		if (poller_rc > rc) {
			rc = poller_rc;
		}
	}

	poller = TAILQ_FIRST(&thread->timer_pollers);
	if (poller) {
		uint64_t now = spdk_get_ticks();

		if (now >= poller->next_run_tick) {
			int timer_rc = 0;

			TAILQ_REMOVE(&thread->timer_pollers, poller, tailq);
			poller->state = SPDK_POLLER_STATE_RUNNING;
			timer_rc = poller->fn(poller->arg);
			if (poller->state == SPDK_POLLER_STATE_UNREGISTERED) {
				free(poller);
			} else {
				poller->state = SPDK_POLLER_STATE_WAITING;
				_spdk_poller_insert_timer(thread, poller, now);
			}

#ifdef DEBUG
			if (timer_rc == -1) {
				SPDK_DEBUGLOG(SPDK_LOG_THREAD, "Timed poller %p returned -1\n", poller);
			}
#endif

			if (timer_rc > rc) {
				rc = timer_rc;

			}
		}
	}

	tls_thread = NULL;

	return rc;
}

uint64_t
spdk_thread_next_poller_expiration(struct spdk_thread *thread)
{
	struct spdk_poller *poller;

	poller = TAILQ_FIRST(&thread->timer_pollers);
	if (poller) {
		return poller->next_run_tick;
	}

	return 0;
}

int
spdk_thread_has_active_pollers(struct spdk_thread *thread)
{
	return !TAILQ_EMPTY(&thread->active_pollers);
}

uint32_t
spdk_thread_get_count(void)
{
	/*
	 * Return cached value of the current thread count.  We could acquire the
	 *  lock and iterate through the TAILQ of threads to count them, but that
	 *  count could still be invalidated after we release the lock.
	 */
	return g_thread_count;
}

struct spdk_thread *
spdk_get_thread(void)
{
	struct spdk_thread *thread;

	thread = _get_thread();
	if (!thread) {
		SPDK_ERRLOG("No thread allocated\n");
	}

	return thread;
}

const char *
spdk_thread_get_name(const struct spdk_thread *thread)
{
	return thread->name;
}

void
spdk_thread_send_msg(const struct spdk_thread *thread, spdk_msg_fn fn, void *ctx)
{
	struct spdk_msg *msg;
	int rc;

	if (!thread) {
		assert(false);
		return;
	}

	if (thread->msg_fn) {
		thread->msg_fn(fn, ctx, thread->thread_ctx);
		return;
	}

	msg = spdk_mempool_get(g_spdk_msg_mempool);
	if (!msg) {
		assert(false);
		return;
	}

	msg->fn = fn;
	msg->arg = ctx;

	rc = spdk_ring_enqueue(thread->messages, (void **)&msg, 1);
	if (rc != 1) {
		assert(false);
		spdk_mempool_put(g_spdk_msg_mempool, msg);
		return;
	}
}

struct spdk_poller *
spdk_poller_register(spdk_poller_fn fn,
		     void *arg,
		     uint64_t period_microseconds)
{
	struct spdk_thread *thread;
	struct spdk_poller *poller;
	uint64_t quotient, remainder, ticks;

	thread = spdk_get_thread();
	if (!thread) {
		assert(false);
		return NULL;
	}

	if (thread->start_poller_fn) {
		return thread->start_poller_fn(thread->thread_ctx, fn, arg, period_microseconds);
	}

	poller = calloc(1, sizeof(*poller));
	if (poller == NULL) {
		SPDK_ERRLOG("Poller memory allocation failed\n");
		return NULL;
	}

	poller->state = SPDK_POLLER_STATE_WAITING;
	poller->fn = fn;
	poller->arg = arg;

	if (period_microseconds) {
		quotient = period_microseconds / SPDK_SEC_TO_USEC;
		remainder = period_microseconds % SPDK_SEC_TO_USEC;
		ticks = spdk_get_ticks_hz();

		poller->period_ticks = ticks * quotient + (ticks * remainder) / SPDK_SEC_TO_USEC;
	} else {
		poller->period_ticks = 0;
	}

	if (poller->period_ticks) {
		_spdk_poller_insert_timer(thread, poller, spdk_get_ticks());
	} else {
		TAILQ_INSERT_TAIL(&thread->active_pollers, poller, tailq);
	}

	return poller;
}

void
spdk_poller_unregister(struct spdk_poller **ppoller)
{
	struct spdk_thread *thread;
	struct spdk_poller *poller;

	poller = *ppoller;
	if (poller == NULL) {
		return;
	}

	*ppoller = NULL;

	thread = spdk_get_thread();
	if (!thread) {
		assert(false);
		return;
	}

	if (thread->stop_poller_fn) {
		thread->stop_poller_fn(poller, thread->thread_ctx);
		return;
	}

	if (poller->state == SPDK_POLLER_STATE_RUNNING) {
		/*
		 * We are being called from the poller_fn, so set the state to unregistered
		 * and let the thread poll loop free the poller.
		 */
		poller->state = SPDK_POLLER_STATE_UNREGISTERED;
	} else {
		/* Poller is not running currently, so just free it. */
		if (poller->period_ticks) {
			TAILQ_REMOVE(&thread->timer_pollers, poller, tailq);
		} else {
			TAILQ_REMOVE(&thread->active_pollers, poller, tailq);
		}

		free(poller);
	}
}

struct call_thread {
	struct spdk_thread *cur_thread;
	spdk_msg_fn fn;
	void *ctx;

	struct spdk_thread *orig_thread;
	spdk_msg_fn cpl;
};

static void
spdk_on_thread(void *ctx)
{
	struct call_thread *ct = ctx;

	ct->fn(ct->ctx);

	pthread_mutex_lock(&g_devlist_mutex);
	ct->cur_thread = TAILQ_NEXT(ct->cur_thread, tailq);
	pthread_mutex_unlock(&g_devlist_mutex);

	if (!ct->cur_thread) {
		SPDK_DEBUGLOG(SPDK_LOG_THREAD, "Completed thread iteration\n");

		spdk_thread_send_msg(ct->orig_thread, ct->cpl, ct->ctx);
		free(ctx);
	} else {
		SPDK_DEBUGLOG(SPDK_LOG_THREAD, "Continuing thread iteration to %s\n",
			      ct->cur_thread->name);

		spdk_thread_send_msg(ct->cur_thread, spdk_on_thread, ctx);
	}
}

void
spdk_for_each_thread(spdk_msg_fn fn, void *ctx, spdk_msg_fn cpl)
{
	struct call_thread *ct;
	struct spdk_thread *thread;

	ct = calloc(1, sizeof(*ct));
	if (!ct) {
		SPDK_ERRLOG("Unable to perform thread iteration\n");
		cpl(ctx);
		return;
	}

	ct->fn = fn;
	ct->ctx = ctx;
	ct->cpl = cpl;

	pthread_mutex_lock(&g_devlist_mutex);
	thread = _get_thread();
	if (!thread) {
		SPDK_ERRLOG("No thread allocated\n");
		free(ct);
		cpl(ctx);
		return;
	}
	ct->orig_thread = thread;
	ct->cur_thread = TAILQ_FIRST(&g_threads);
	pthread_mutex_unlock(&g_devlist_mutex);

	SPDK_DEBUGLOG(SPDK_LOG_THREAD, "Starting thread iteration from %s\n",
		      ct->orig_thread->name);

	spdk_thread_send_msg(ct->cur_thread, spdk_on_thread, ct);
}

void
spdk_io_device_register(void *io_device, spdk_io_channel_create_cb create_cb,
			spdk_io_channel_destroy_cb destroy_cb, uint32_t ctx_size,
			const char *name)
{
	struct io_device *dev, *tmp;
	struct spdk_thread *thread;

	assert(io_device != NULL);
	assert(create_cb != NULL);
	assert(destroy_cb != NULL);

	thread = spdk_get_thread();
	if (!thread) {
		SPDK_ERRLOG("%s called from non-SPDK thread\n", __func__);
		assert(false);
		return;
	}

	dev = calloc(1, sizeof(struct io_device));
	if (dev == NULL) {
		SPDK_ERRLOG("could not allocate io_device\n");
		return;
	}

	dev->io_device = io_device;
	if (name) {
		dev->name = strdup(name);
	} else {
		dev->name = spdk_sprintf_alloc("%p", dev);
	}
	dev->create_cb = create_cb;
	dev->destroy_cb = destroy_cb;
	dev->unregister_cb = NULL;
	dev->ctx_size = ctx_size;
	dev->for_each_count = 0;
	dev->unregistered = false;
	dev->refcnt = 0;

	SPDK_DEBUGLOG(SPDK_LOG_THREAD, "Registering io_device %s (%p) on thread %s\n",
		      dev->name, dev->io_device, thread->name);

	pthread_mutex_lock(&g_devlist_mutex);
	TAILQ_FOREACH(tmp, &g_io_devices, tailq) {
		if (tmp->io_device == io_device) {
			SPDK_ERRLOG("io_device %p already registered (old:%s new:%s)\n",
				    io_device, tmp->name, dev->name);
			free(dev->name);
			free(dev);
			pthread_mutex_unlock(&g_devlist_mutex);
			return;
		}
	}
	TAILQ_INSERT_TAIL(&g_io_devices, dev, tailq);
	pthread_mutex_unlock(&g_devlist_mutex);
}

static void
_finish_unregister(void *arg)
{
	struct io_device *dev = arg;

	SPDK_DEBUGLOG(SPDK_LOG_THREAD, "Finishing unregistration of io_device %s (%p) on thread %s\n",
		      dev->name, dev->io_device, dev->unregister_thread->name);

	dev->unregister_cb(dev->io_device);
	free(dev->name);
	free(dev);
}

static void
_spdk_io_device_free(struct io_device *dev)
{
	if (dev->unregister_cb == NULL) {
		free(dev->name);
		free(dev);
	} else {
		assert(dev->unregister_thread != NULL);
		SPDK_DEBUGLOG(SPDK_LOG_THREAD, "io_device %s (%p) needs to unregister from thread %s\n",
			      dev->name, dev->io_device, dev->unregister_thread->name);
		spdk_thread_send_msg(dev->unregister_thread, _finish_unregister, dev);
	}
}

void
spdk_io_device_unregister(void *io_device, spdk_io_device_unregister_cb unregister_cb)
{
	struct io_device *dev;
	uint32_t refcnt;
	struct spdk_thread *thread;

	thread = spdk_get_thread();
	if (!thread) {
		SPDK_ERRLOG("%s called from non-SPDK thread\n", __func__);
		assert(false);
		return;
	}

	pthread_mutex_lock(&g_devlist_mutex);
	TAILQ_FOREACH(dev, &g_io_devices, tailq) {
		if (dev->io_device == io_device) {
			break;
		}
	}

	if (!dev) {
		SPDK_ERRLOG("io_device %p not found\n", io_device);
		assert(false);
		pthread_mutex_unlock(&g_devlist_mutex);
		return;
	}

	if (dev->for_each_count > 0) {
		SPDK_ERRLOG("io_device %s (%p) has %u for_each calls outstanding\n",
			    dev->name, io_device, dev->for_each_count);
		pthread_mutex_unlock(&g_devlist_mutex);
		return;
	}

	dev->unregister_cb = unregister_cb;
	dev->unregistered = true;
	TAILQ_REMOVE(&g_io_devices, dev, tailq);
	refcnt = dev->refcnt;
	dev->unregister_thread = thread;
	pthread_mutex_unlock(&g_devlist_mutex);

	SPDK_DEBUGLOG(SPDK_LOG_THREAD, "Unregistering io_device %s (%p) from thread %s\n",
		      dev->name, dev->io_device, thread->name);

	if (refcnt > 0) {
		/* defer deletion */
		return;
	}

	_spdk_io_device_free(dev);
}

struct spdk_io_channel *
spdk_get_io_channel(void *io_device)
{
	struct spdk_io_channel *ch;
	struct spdk_thread *thread;
	struct io_device *dev;
	int rc;

	pthread_mutex_lock(&g_devlist_mutex);
	TAILQ_FOREACH(dev, &g_io_devices, tailq) {
		if (dev->io_device == io_device) {
			break;
		}
	}
	if (dev == NULL) {
		SPDK_ERRLOG("could not find io_device %p\n", io_device);
		pthread_mutex_unlock(&g_devlist_mutex);
		return NULL;
	}

	thread = _get_thread();
	if (!thread) {
		SPDK_ERRLOG("No thread allocated\n");
		pthread_mutex_unlock(&g_devlist_mutex);
		return NULL;
	}

	TAILQ_FOREACH(ch, &thread->io_channels, tailq) {
		if (ch->dev == dev) {
			ch->ref++;

			SPDK_DEBUGLOG(SPDK_LOG_THREAD, "Get io_channel %p for io_device %s (%p) on thread %s refcnt %u\n",
				      ch, dev->name, dev->io_device, thread->name, ch->ref);

			/*
			 * An I/O channel already exists for this device on this
			 *  thread, so return it.
			 */
			pthread_mutex_unlock(&g_devlist_mutex);
			return ch;
		}
	}

	ch = calloc(1, sizeof(*ch) + dev->ctx_size);
	if (ch == NULL) {
		SPDK_ERRLOG("could not calloc spdk_io_channel\n");
		pthread_mutex_unlock(&g_devlist_mutex);
		return NULL;
	}

	ch->dev = dev;
	ch->destroy_cb = dev->destroy_cb;
	ch->thread = thread;
	ch->ref = 1;
	ch->destroy_ref = 0;
	TAILQ_INSERT_TAIL(&thread->io_channels, ch, tailq);

	SPDK_DEBUGLOG(SPDK_LOG_THREAD, "Get io_channel %p for io_device %s (%p) on thread %s refcnt %u\n",
		      ch, dev->name, dev->io_device, thread->name, ch->ref);

	dev->refcnt++;

	pthread_mutex_unlock(&g_devlist_mutex);

	rc = dev->create_cb(io_device, (uint8_t *)ch + sizeof(*ch));
	if (rc != 0) {
		pthread_mutex_lock(&g_devlist_mutex);
		TAILQ_REMOVE(&ch->thread->io_channels, ch, tailq);
		dev->refcnt--;
		free(ch);
		pthread_mutex_unlock(&g_devlist_mutex);
		return NULL;
	}

	return ch;
}

static void
_spdk_put_io_channel(void *arg)
{
	struct spdk_io_channel *ch = arg;
	bool do_remove_dev = true;
	struct spdk_thread *thread;

	thread = spdk_get_thread();
	if (!thread) {
		SPDK_ERRLOG("%s called from non-SPDK thread\n", __func__);
		assert(false);
		return;
	}

	SPDK_DEBUGLOG(SPDK_LOG_THREAD,
		      "Releasing io_channel %p for io_device %s (%p). Channel thread %p. Current thread %s\n",
		      ch, ch->dev->name, ch->dev->io_device, ch->thread, thread->name);

	assert(ch->thread == thread);

	ch->destroy_ref--;

	if (ch->ref > 0 || ch->destroy_ref > 0) {
		/*
		 * Another reference to the associated io_device was requested
		 *  after this message was sent but before it had a chance to
		 *  execute.
		 */
		return;
	}

	pthread_mutex_lock(&g_devlist_mutex);
	TAILQ_REMOVE(&ch->thread->io_channels, ch, tailq);
	pthread_mutex_unlock(&g_devlist_mutex);

	/* Don't hold the devlist mutex while the destroy_cb is called. */
	ch->destroy_cb(ch->dev->io_device, spdk_io_channel_get_ctx(ch));

	pthread_mutex_lock(&g_devlist_mutex);
	ch->dev->refcnt--;

	if (!ch->dev->unregistered) {
		do_remove_dev = false;
	}

	if (ch->dev->refcnt > 0) {
		do_remove_dev = false;
	}

	pthread_mutex_unlock(&g_devlist_mutex);

	if (do_remove_dev) {
		_spdk_io_device_free(ch->dev);
	}
	free(ch);
}

void
spdk_put_io_channel(struct spdk_io_channel *ch)
{
	SPDK_DEBUGLOG(SPDK_LOG_THREAD,
		      "Putting io_channel %p for io_device %s (%p) on thread %s refcnt %u\n",
		      ch, ch->dev->name, ch->dev->io_device, ch->thread->name, ch->ref);

	ch->ref--;

	if (ch->ref == 0) {
		ch->destroy_ref++;
		spdk_thread_send_msg(ch->thread, _spdk_put_io_channel, ch);
	}
}

struct spdk_io_channel *
spdk_io_channel_from_ctx(void *ctx)
{
	return (struct spdk_io_channel *)((uint8_t *)ctx - sizeof(struct spdk_io_channel));
}

struct spdk_thread *
spdk_io_channel_get_thread(struct spdk_io_channel *ch)
{
	return ch->thread;
}

struct spdk_io_channel_iter {
	void *io_device;
	struct io_device *dev;
	spdk_channel_msg fn;
	int status;
	void *ctx;
	struct spdk_io_channel *ch;

	struct spdk_thread *cur_thread;

	struct spdk_thread *orig_thread;
	spdk_channel_for_each_cpl cpl;
};

void *
spdk_io_channel_iter_get_io_device(struct spdk_io_channel_iter *i)
{
	return i->io_device;
}

struct spdk_io_channel *
spdk_io_channel_iter_get_channel(struct spdk_io_channel_iter *i)
{
	return i->ch;
}

void *
spdk_io_channel_iter_get_ctx(struct spdk_io_channel_iter *i)
{
	return i->ctx;
}

static void
_call_completion(void *ctx)
{
	struct spdk_io_channel_iter *i = ctx;

	if (i->cpl != NULL) {
		i->cpl(i, i->status);
	}
	free(i);
}

static void
_call_channel(void *ctx)
{
	struct spdk_io_channel_iter *i = ctx;
	struct spdk_io_channel *ch;

	/*
	 * It is possible that the channel was deleted before this
	 *  message had a chance to execute.  If so, skip calling
	 *  the fn() on this thread.
	 */
	pthread_mutex_lock(&g_devlist_mutex);
	TAILQ_FOREACH(ch, &i->cur_thread->io_channels, tailq) {
		if (ch->dev->io_device == i->io_device) {
			break;
		}
	}
	pthread_mutex_unlock(&g_devlist_mutex);

	if (ch) {
		i->fn(i);
	} else {
		spdk_for_each_channel_continue(i, 0);
	}
}

void
spdk_for_each_channel(void *io_device, spdk_channel_msg fn, void *ctx,
		      spdk_channel_for_each_cpl cpl)
{
	struct spdk_thread *thread;
	struct spdk_io_channel *ch;
	struct spdk_io_channel_iter *i;

	i = calloc(1, sizeof(*i));
	if (!i) {
		SPDK_ERRLOG("Unable to allocate iterator\n");
		return;
	}

	i->io_device = io_device;
	i->fn = fn;
	i->ctx = ctx;
	i->cpl = cpl;

	pthread_mutex_lock(&g_devlist_mutex);
	i->orig_thread = _get_thread();

	TAILQ_FOREACH(thread, &g_threads, tailq) {
		TAILQ_FOREACH(ch, &thread->io_channels, tailq) {
			if (ch->dev->io_device == io_device) {
				ch->dev->for_each_count++;
				i->dev = ch->dev;
				i->cur_thread = thread;
				i->ch = ch;
				pthread_mutex_unlock(&g_devlist_mutex);
				spdk_thread_send_msg(thread, _call_channel, i);
				return;
			}
		}
	}

	pthread_mutex_unlock(&g_devlist_mutex);

	spdk_thread_send_msg(i->orig_thread, _call_completion, i);
}

void
spdk_for_each_channel_continue(struct spdk_io_channel_iter *i, int status)
{
	struct spdk_thread *thread;
	struct spdk_io_channel *ch;

	assert(i->cur_thread == spdk_get_thread());

	i->status = status;

	pthread_mutex_lock(&g_devlist_mutex);
	if (status) {
		goto end;
	}
	thread = TAILQ_NEXT(i->cur_thread, tailq);
	while (thread) {
		TAILQ_FOREACH(ch, &thread->io_channels, tailq) {
			if (ch->dev->io_device == i->io_device) {
				i->cur_thread = thread;
				i->ch = ch;
				pthread_mutex_unlock(&g_devlist_mutex);
				spdk_thread_send_msg(thread, _call_channel, i);
				return;
			}
		}
		thread = TAILQ_NEXT(thread, tailq);
	}

end:
	i->dev->for_each_count--;
	i->ch = NULL;
	pthread_mutex_unlock(&g_devlist_mutex);

	spdk_thread_send_msg(i->orig_thread, _call_completion, i);
}


SPDK_LOG_REGISTER_COMPONENT("thread", SPDK_LOG_THREAD)