thread-pool.c - third_party/qemu - Git at Google

 /*
  * QEMU block layer thread pool
  *
  * Copyright IBM, Corp. 2008
  * Copyright Red Hat, Inc. 2012
  *
  * Authors:
  *  Anthony Liguori   <aliguori@us.ibm.com>
  *  Paolo Bonzini     <pbonzini@redhat.com>
  *
  * This work is licensed under the terms of the GNU GPL, version 2.  See
  * the COPYING file in the top-level directory.
  *
  * Contributions after 2012-01-13 are licensed under the terms of the
  * GNU GPL, version 2 or (at your option) any later version.
  */
 #include "qemu-common.h"
 #include "qemu/queue.h"
 #include "qemu/thread.h"
 #include "qemu/osdep.h"
 #include "block/coroutine.h"
 #include "trace.h"
 #include "block/block_int.h"
 #include "qemu/event_notifier.h"
 #include "block/thread-pool.h"

 static void do_spawn_thread(void);

 typedef struct ThreadPoolElement ThreadPoolElement;

 enum ThreadState {
     THREAD_QUEUED,
     THREAD_ACTIVE,
     THREAD_DONE,
     THREAD_CANCELED,
 };

 struct ThreadPoolElement {
     BlockDriverAIOCB common;
     ThreadPoolFunc *func;
     void *arg;

     /* Moving state out of THREAD_QUEUED is protected by lock.  After
      * that, only the worker thread can write to it.  Reads and writes
      * of state and ret are ordered with memory barriers.
      */
     enum ThreadState state;
     int ret;

     /* Access to this list is protected by lock.  */
     QTAILQ_ENTRY(ThreadPoolElement) reqs;

     /* Access to this list is protected by the global mutex.  */
     QLIST_ENTRY(ThreadPoolElement) all;
 };

 static EventNotifier notifier;
 static QemuMutex lock;
 static QemuCond check_cancel;
 static QemuSemaphore sem;
 static int max_threads = 64;
 static QEMUBH *new_thread_bh;

 /* The following variables are protected by the global mutex.  */
 static QLIST_HEAD(, ThreadPoolElement) head;

 /* The following variables are protected by lock.  */
 static QTAILQ_HEAD(, ThreadPoolElement) request_list;
 static int cur_threads;
 static int idle_threads;
 static int new_threads;     /* backlog of threads we need to create */
 static int pending_threads; /* threads created but not running yet */
 static int pending_cancellations; /* whether we need a cond_broadcast */

 static void *worker_thread(void *unused)
 {
     qemu_mutex_lock(&lock);
     pending_threads--;
     do_spawn_thread();

     while (1) {
         ThreadPoolElement *req;
         int ret;

         do {
             idle_threads++;
             qemu_mutex_unlock(&lock);
             ret = qemu_sem_timedwait(&sem, 10000);
             qemu_mutex_lock(&lock);
             idle_threads--;
         } while (ret == -1 && !QTAILQ_EMPTY(&request_list));
         if (ret == -1) {
             break;
         }

         req = QTAILQ_FIRST(&request_list);
         QTAILQ_REMOVE(&request_list, req, reqs);
         req->state = THREAD_ACTIVE;
         qemu_mutex_unlock(&lock);

         ret = req->func(req->arg);

         req->ret = ret;
         /* Write ret before state.  */
         smp_wmb();
         req->state = THREAD_DONE;

         qemu_mutex_lock(&lock);
         if (pending_cancellations) {
             qemu_cond_broadcast(&check_cancel);
         }

         event_notifier_set(&notifier);
     }

     cur_threads--;
     qemu_mutex_unlock(&lock);
     return NULL;
 }

 static void do_spawn_thread(void)
 {
     QemuThread t;

     /* Runs with lock taken.  */
     if (!new_threads) {
         return;
     }

     new_threads--;
     pending_threads++;

     qemu_thread_create(&t, worker_thread, NULL, QEMU_THREAD_DETACHED);
 }

 static void spawn_thread_bh_fn(void *opaque)
 {
     qemu_mutex_lock(&lock);
     do_spawn_thread();
     qemu_mutex_unlock(&lock);
 }

 static void spawn_thread(void)
 {
     cur_threads++;
     new_threads++;
     /* If there are threads being created, they will spawn new workers, so
      * we don't spend time creating many threads in a loop holding a mutex or
      * starving the current vcpu.
      *
      * If there are no idle threads, ask the main thread to create one, so we
      * inherit the correct affinity instead of the vcpu affinity.
      */
     if (!pending_threads) {
         qemu_bh_schedule(new_thread_bh);
     }
 }

 static void event_notifier_ready(EventNotifier *notifier)
 {
     ThreadPoolElement *elem, *next;

     event_notifier_test_and_clear(notifier);
 restart:
     QLIST_FOREACH_SAFE(elem, &head, all, next) {
         if (elem->state != THREAD_CANCELED && elem->state != THREAD_DONE) {
             continue;
         }
         if (elem->state == THREAD_DONE) {
             trace_thread_pool_complete(elem, elem->common.opaque, elem->ret);
         }
         if (elem->state == THREAD_DONE && elem->common.cb) {
             QLIST_REMOVE(elem, all);
             /* Read state before ret.  */
             smp_rmb();
             elem->common.cb(elem->common.opaque, elem->ret);
             qemu_aio_release(elem);
             goto restart;
         } else {
             /* remove the request */
             QLIST_REMOVE(elem, all);
             qemu_aio_release(elem);
         }
     }
 }

 static int thread_pool_active(EventNotifier *notifier)
 {
     return !QLIST_EMPTY(&head);
 }

 static void thread_pool_cancel(BlockDriverAIOCB *acb)
 {
     ThreadPoolElement *elem = (ThreadPoolElement *)acb;

     trace_thread_pool_cancel(elem, elem->common.opaque);

     qemu_mutex_lock(&lock);
     if (elem->state == THREAD_QUEUED &&
         /* No thread has yet started working on elem. we can try to "steal"
          * the item from the worker if we can get a signal from the
          * semaphore.  Because this is non-blocking, we can do it with
          * the lock taken and ensure that elem will remain THREAD_QUEUED.
          */
         qemu_sem_timedwait(&sem, 0) == 0) {
         QTAILQ_REMOVE(&request_list, elem, reqs);
         elem->state = THREAD_CANCELED;
         event_notifier_set(&notifier);
     } else {
         pending_cancellations++;
         while (elem->state != THREAD_CANCELED && elem->state != THREAD_DONE) {
             qemu_cond_wait(&check_cancel, &lock);
         }
         pending_cancellations--;
     }
     qemu_mutex_unlock(&lock);
 }

 static const AIOCBInfo thread_pool_aiocb_info = {
     .aiocb_size         = sizeof(ThreadPoolElement),
     .cancel             = thread_pool_cancel,
 };

 BlockDriverAIOCB *thread_pool_submit_aio(ThreadPoolFunc *func, void *arg,
         BlockDriverCompletionFunc *cb, void *opaque)
 {
     ThreadPoolElement *req;

     req = qemu_aio_get(&thread_pool_aiocb_info, NULL, cb, opaque);
     req->func = func;
     req->arg = arg;
     req->state = THREAD_QUEUED;

     QLIST_INSERT_HEAD(&head, req, all);

     trace_thread_pool_submit(req, arg);

     qemu_mutex_lock(&lock);
     if (idle_threads == 0 && cur_threads < max_threads) {
         spawn_thread();
     }
     QTAILQ_INSERT_TAIL(&request_list, req, reqs);
     qemu_mutex_unlock(&lock);
     qemu_sem_post(&sem);
     return &req->common;
 }

 typedef struct ThreadPoolCo {
     Coroutine *co;
     int ret;
 } ThreadPoolCo;

 static void thread_pool_co_cb(void *opaque, int ret)
 {
     ThreadPoolCo *co = opaque;

     co->ret = ret;
     qemu_coroutine_enter(co->co, NULL);
 }

 int coroutine_fn thread_pool_submit_co(ThreadPoolFunc *func, void *arg)
 {
     ThreadPoolCo tpc = { .co = qemu_coroutine_self(), .ret = -EINPROGRESS };
     assert(qemu_in_coroutine());
     thread_pool_submit_aio(func, arg, thread_pool_co_cb, &tpc);
     qemu_coroutine_yield();
     return tpc.ret;
 }

 void thread_pool_submit(ThreadPoolFunc *func, void *arg)
 {
     thread_pool_submit_aio(func, arg, NULL, NULL);
 }

 static void thread_pool_init(void)
 {
     QLIST_INIT(&head);
     event_notifier_init(&notifier, false);
     qemu_mutex_init(&lock);
     qemu_cond_init(&check_cancel);
     qemu_sem_init(&sem, 0);
     qemu_aio_set_event_notifier(&notifier, event_notifier_ready,
                                 thread_pool_active);

     QTAILQ_INIT(&request_list);
     new_thread_bh = qemu_bh_new(spawn_thread_bh_fn, NULL);
 }

 block_init(thread_pool_init)
	/*
	* QEMU block layer thread pool
	*
	* Copyright IBM, Corp. 2008
	* Copyright Red Hat, Inc. 2012
	*
	* Authors:
	* Anthony Liguori <aliguori@us.ibm.com>
	* Paolo Bonzini <pbonzini@redhat.com>
	*
	* This work is licensed under the terms of the GNU GPL, version 2. See
	* the COPYING file in the top-level directory.
	*
	* Contributions after 2012-01-13 are licensed under the terms of the
	* GNU GPL, version 2 or (at your option) any later version.
	*/
	#include "qemu-common.h"
	#include "qemu/queue.h"
	#include "qemu/thread.h"
	#include "qemu/osdep.h"
	#include "block/coroutine.h"
	#include "trace.h"
	#include "block/block_int.h"
	#include "qemu/event_notifier.h"
	#include "block/thread-pool.h"

	static void do_spawn_thread(void);

	typedef struct ThreadPoolElement ThreadPoolElement;

	enum ThreadState {
	THREAD_QUEUED,
	THREAD_ACTIVE,
	THREAD_DONE,
	THREAD_CANCELED,
	};

	struct ThreadPoolElement {
	BlockDriverAIOCB common;
	ThreadPoolFunc *func;
	void *arg;

	/* Moving state out of THREAD_QUEUED is protected by lock. After
	* that, only the worker thread can write to it. Reads and writes
	* of state and ret are ordered with memory barriers.
	*/
	enum ThreadState state;
	int ret;

	/* Access to this list is protected by lock. */
	QTAILQ_ENTRY(ThreadPoolElement) reqs;

	/* Access to this list is protected by the global mutex. */
	QLIST_ENTRY(ThreadPoolElement) all;
	};

	static EventNotifier notifier;
	static QemuMutex lock;
	static QemuCond check_cancel;
	static QemuSemaphore sem;
	static int max_threads = 64;
	static QEMUBH *new_thread_bh;

	/* The following variables are protected by the global mutex. */
	static QLIST_HEAD(, ThreadPoolElement) head;

	/* The following variables are protected by lock. */
	static QTAILQ_HEAD(, ThreadPoolElement) request_list;
	static int cur_threads;
	static int idle_threads;
	static int new_threads; /* backlog of threads we need to create */
	static int pending_threads; /* threads created but not running yet */
	static int pending_cancellations; /* whether we need a cond_broadcast */

	static void worker_thread(void unused)
	{
	qemu_mutex_lock(&lock);
	pending_threads--;
	do_spawn_thread();

	while (1) {
	ThreadPoolElement *req;
	int ret;

	do {
	idle_threads++;
	qemu_mutex_unlock(&lock);
	ret = qemu_sem_timedwait(&sem, 10000);
	qemu_mutex_lock(&lock);
	idle_threads--;
	} while (ret == -1 && !QTAILQ_EMPTY(&request_list));
	if (ret == -1) {
	break;
	}

	req = QTAILQ_FIRST(&request_list);
	QTAILQ_REMOVE(&request_list, req, reqs);
	req->state = THREAD_ACTIVE;
	qemu_mutex_unlock(&lock);

	ret = req->func(req->arg);

	req->ret = ret;
	/* Write ret before state. */
	smp_wmb();
	req->state = THREAD_DONE;

	qemu_mutex_lock(&lock);
	if (pending_cancellations) {
	qemu_cond_broadcast(&check_cancel);
	}

	event_notifier_set(&notifier);
	}

	cur_threads--;
	qemu_mutex_unlock(&lock);
	return NULL;
	}

	static void do_spawn_thread(void)
	{
	QemuThread t;

	/* Runs with lock taken. */
	if (!new_threads) {
	return;
	}

	new_threads--;
	pending_threads++;

	qemu_thread_create(&t, worker_thread, NULL, QEMU_THREAD_DETACHED);
	}

	static void spawn_thread_bh_fn(void *opaque)
	{
	qemu_mutex_lock(&lock);
	do_spawn_thread();
	qemu_mutex_unlock(&lock);
	}

	static void spawn_thread(void)
	{
	cur_threads++;
	new_threads++;
	/* If there are threads being created, they will spawn new workers, so
	* we don't spend time creating many threads in a loop holding a mutex or
	* starving the current vcpu.
	*
	* If there are no idle threads, ask the main thread to create one, so we
	* inherit the correct affinity instead of the vcpu affinity.
	*/
	if (!pending_threads) {
	qemu_bh_schedule(new_thread_bh);
	}
	}

	static void event_notifier_ready(EventNotifier *notifier)
	{
	ThreadPoolElement elem, next;

	event_notifier_test_and_clear(notifier);
	restart:
	QLIST_FOREACH_SAFE(elem, &head, all, next) {
	if (elem->state != THREAD_CANCELED && elem->state != THREAD_DONE) {
	continue;
	}
	if (elem->state == THREAD_DONE) {
	trace_thread_pool_complete(elem, elem->common.opaque, elem->ret);
	}
	if (elem->state == THREAD_DONE && elem->common.cb) {
	QLIST_REMOVE(elem, all);
	/* Read state before ret. */
	smp_rmb();
	elem->common.cb(elem->common.opaque, elem->ret);
	qemu_aio_release(elem);
	goto restart;
	} else {
	/* remove the request */
	QLIST_REMOVE(elem, all);
	qemu_aio_release(elem);
	}
	}
	}

	static int thread_pool_active(EventNotifier *notifier)
	{
	return !QLIST_EMPTY(&head);
	}

	static void thread_pool_cancel(BlockDriverAIOCB *acb)
	{
	ThreadPoolElement elem = (ThreadPoolElement )acb;

	trace_thread_pool_cancel(elem, elem->common.opaque);

	qemu_mutex_lock(&lock);
	if (elem->state == THREAD_QUEUED &&
	/* No thread has yet started working on elem. we can try to "steal"
	* the item from the worker if we can get a signal from the
	* semaphore. Because this is non-blocking, we can do it with
	* the lock taken and ensure that elem will remain THREAD_QUEUED.
	*/
	qemu_sem_timedwait(&sem, 0) == 0) {
	QTAILQ_REMOVE(&request_list, elem, reqs);
	elem->state = THREAD_CANCELED;
	event_notifier_set(&notifier);
	} else {
	pending_cancellations++;
	while (elem->state != THREAD_CANCELED && elem->state != THREAD_DONE) {
	qemu_cond_wait(&check_cancel, &lock);
	}
	pending_cancellations--;
	}
	qemu_mutex_unlock(&lock);
	}

	static const AIOCBInfo thread_pool_aiocb_info = {
	.aiocb_size = sizeof(ThreadPoolElement),
	.cancel = thread_pool_cancel,
	};

	BlockDriverAIOCB thread_pool_submit_aio(ThreadPoolFunc func, void *arg,
	BlockDriverCompletionFunc cb, void opaque)
	{
	ThreadPoolElement *req;

	req = qemu_aio_get(&thread_pool_aiocb_info, NULL, cb, opaque);
	req->func = func;
	req->arg = arg;
	req->state = THREAD_QUEUED;

	QLIST_INSERT_HEAD(&head, req, all);

	trace_thread_pool_submit(req, arg);

	qemu_mutex_lock(&lock);
	if (idle_threads == 0 && cur_threads < max_threads) {
	spawn_thread();
	}
	QTAILQ_INSERT_TAIL(&request_list, req, reqs);
	qemu_mutex_unlock(&lock);
	qemu_sem_post(&sem);
	return &req->common;
	}

	typedef struct ThreadPoolCo {
	Coroutine *co;
	int ret;
	} ThreadPoolCo;

	static void thread_pool_co_cb(void *opaque, int ret)
	{
	ThreadPoolCo *co = opaque;

	co->ret = ret;
	qemu_coroutine_enter(co->co, NULL);
	}

	int coroutine_fn thread_pool_submit_co(ThreadPoolFunc func, void arg)
	{
	ThreadPoolCo tpc = { .co = qemu_coroutine_self(), .ret = -EINPROGRESS };
	assert(qemu_in_coroutine());
	thread_pool_submit_aio(func, arg, thread_pool_co_cb, &tpc);
	qemu_coroutine_yield();
	return tpc.ret;
	}

	void thread_pool_submit(ThreadPoolFunc func, void arg)
	{
	thread_pool_submit_aio(func, arg, NULL, NULL);
	}

	static void thread_pool_init(void)
	{
	QLIST_INIT(&head);
	event_notifier_init(&notifier, false);
	qemu_mutex_init(&lock);
	qemu_cond_init(&check_cancel);
	qemu_sem_init(&sem, 0);
	qemu_aio_set_event_notifier(&notifier, event_notifier_ready,
	thread_pool_active);

	QTAILQ_INIT(&request_list);
	new_thread_bh = qemu_bh_new(spawn_thread_bh_fn, NULL);
	}

	block_init(thread_pool_init)