diff --git a/util/thread-pool.c b/util/thread-pool.c index 4979f30ca3..6e3d4e4a2f 100644 --- a/util/thread-pool.c +++ b/util/thread-pool.c @@ -57,7 +57,7 @@ struct ThreadPool { QEMUBH *completion_bh; QemuMutex lock; QemuCond worker_stopped; - QemuSemaphore sem; + QemuCond request_cond; QEMUBH *new_thread_bh; /* The following variables are only accessed from one AioContext. */ @@ -74,23 +74,6 @@ struct ThreadPool { int max_threads; }; -static inline bool back_to_sleep(ThreadPool *pool, int ret) -{ - /* - * The semaphore timed out, we should exit the loop except when: - * - There is work to do, we raced with the signal. - * - The max threads threshold just changed, we raced with the signal. - * - The thread pool forces a minimum number of readily available threads. - */ - if (ret == -1 && (!QTAILQ_EMPTY(&pool->request_list) || - pool->cur_threads > pool->max_threads || - pool->cur_threads <= pool->min_threads)) { - return true; - } - - return false; -} - static void *worker_thread(void *opaque) { ThreadPool *pool = opaque; @@ -99,20 +82,25 @@ static void *worker_thread(void *opaque) pool->pending_threads--; do_spawn_thread(pool); - while (!pool->stopping) { + while (!pool->stopping && pool->cur_threads <= pool->max_threads) { ThreadPoolElement *req; int ret; - do { + if (QTAILQ_EMPTY(&pool->request_list)) { pool->idle_threads++; - qemu_mutex_unlock(&pool->lock); - ret = qemu_sem_timedwait(&pool->sem, 10000); - qemu_mutex_lock(&pool->lock); + ret = qemu_cond_timedwait(&pool->request_cond, &pool->lock, 10000); pool->idle_threads--; - } while (back_to_sleep(pool, ret)); - if (ret == -1 || pool->stopping || - pool->cur_threads > pool->max_threads) { - break; + if (ret == 0 && + QTAILQ_EMPTY(&pool->request_list) && + pool->cur_threads > pool->min_threads) { + /* Timed out + no work to do + no need for warm threads = exit. */ + break; + } + /* + * Even if there was some work to do, check if there aren't + * too many worker threads before picking it up. + */ + continue; } req = QTAILQ_FIRST(&pool->request_list); @@ -134,6 +122,12 @@ static void *worker_thread(void *opaque) pool->cur_threads--; qemu_cond_signal(&pool->worker_stopped); qemu_mutex_unlock(&pool->lock); + + /* + * Wake up another thread, in case we got a wakeup but decided + * to exit due to pool->cur_threads > pool->max_threads. + */ + qemu_cond_signal(&pool->request_cond); return NULL; } @@ -229,13 +223,7 @@ static void thread_pool_cancel(BlockAIOCB *acb) trace_thread_pool_cancel(elem, elem->common.opaque); QEMU_LOCK_GUARD(&pool->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(&pool->sem, 0) == 0) { + if (elem->state == THREAD_QUEUED) { QTAILQ_REMOVE(&pool->request_list, elem, reqs); qemu_bh_schedule(pool->completion_bh); @@ -280,7 +268,7 @@ BlockAIOCB *thread_pool_submit_aio(ThreadPool *pool, } QTAILQ_INSERT_TAIL(&pool->request_list, req, reqs); qemu_mutex_unlock(&pool->lock); - qemu_sem_post(&pool->sem); + qemu_cond_signal(&pool->request_cond); return &req->common; } @@ -323,7 +311,7 @@ void thread_pool_update_params(ThreadPool *pool, AioContext *ctx) * We either have to: * - Increase the number available of threads until over the min_threads * threshold. - * - Decrease the number of available threads until under the max_threads + * - Bump the worker threads so that they exit, until under the max_threads * threshold. * - Do nothing. The current number of threads fall in between the min and * max thresholds. We'll let the pool manage itself. @@ -333,7 +321,7 @@ void thread_pool_update_params(ThreadPool *pool, AioContext *ctx) } for (int i = pool->cur_threads; i > pool->max_threads; i--) { - qemu_sem_post(&pool->sem); + qemu_cond_signal(&pool->request_cond); } qemu_mutex_unlock(&pool->lock); @@ -350,7 +338,7 @@ static void thread_pool_init_one(ThreadPool *pool, AioContext *ctx) pool->completion_bh = aio_bh_new(ctx, thread_pool_completion_bh, pool); qemu_mutex_init(&pool->lock); qemu_cond_init(&pool->worker_stopped); - qemu_sem_init(&pool->sem, 0); + qemu_cond_init(&pool->request_cond); pool->new_thread_bh = aio_bh_new(ctx, spawn_thread_bh_fn, pool); QLIST_INIT(&pool->head); @@ -383,15 +371,15 @@ void thread_pool_free(ThreadPool *pool) /* Wait for worker threads to terminate */ pool->stopping = true; + qemu_cond_broadcast(&pool->request_cond); while (pool->cur_threads > 0) { - qemu_sem_post(&pool->sem); qemu_cond_wait(&pool->worker_stopped, &pool->lock); } qemu_mutex_unlock(&pool->lock); qemu_bh_delete(pool->completion_bh); - qemu_sem_destroy(&pool->sem); + qemu_cond_destroy(&pool->request_cond); qemu_cond_destroy(&pool->worker_stopped); qemu_mutex_destroy(&pool->lock); g_free(pool);