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-rw-r--r--thread-pool.c289
1 files changed, 289 insertions, 0 deletions
diff --git a/thread-pool.c b/thread-pool.c
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index 0000000000..e3ca64d790
--- /dev/null
+++ b/thread-pool.c
@@ -0,0 +1,289 @@
+/*
+ * 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)
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