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/*
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* QEMU block layer thread pool
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*
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* Copyright IBM, Corp. 2008
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* Copyright Red Hat, Inc. 2012
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*
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* Authors:
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* Anthony Liguori <aliguori@us.ibm.com>
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* Paolo Bonzini <pbonzini@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2. See
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* the COPYING file in the top-level directory.
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*
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* Contributions after 2012-01-13 are licensed under the terms of the
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* GNU GPL, version 2 or (at your option) any later version.
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*/
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#include "qemu-common.h" |
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#include "qemu/queue.h" |
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#include "qemu/thread.h" |
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#include "qemu/osdep.h" |
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#include "block/coroutine.h" |
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#include "trace.h" |
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#include "block/block_int.h" |
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#include "qemu/event_notifier.h" |
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#include "block/thread-pool.h" |
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static void do_spawn_thread(void); |
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typedef struct ThreadPoolElement ThreadPoolElement; |
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enum ThreadState {
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THREAD_QUEUED, |
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THREAD_ACTIVE, |
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THREAD_DONE, |
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THREAD_CANCELED, |
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}; |
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struct ThreadPoolElement {
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BlockDriverAIOCB common; |
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ThreadPoolFunc *func; |
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void *arg;
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/* Moving state out of THREAD_QUEUED is protected by lock. After
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* that, only the worker thread can write to it. Reads and writes
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* of state and ret are ordered with memory barriers.
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*/
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enum ThreadState state;
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int ret;
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/* Access to this list is protected by lock. */
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QTAILQ_ENTRY(ThreadPoolElement) reqs; |
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/* Access to this list is protected by the global mutex. */
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QLIST_ENTRY(ThreadPoolElement) all; |
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}; |
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static EventNotifier notifier;
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static QemuMutex lock;
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static QemuCond check_cancel;
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static QemuSemaphore sem;
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static int max_threads = 64; |
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static QEMUBH *new_thread_bh;
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/* The following variables are protected by the global mutex. */
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static QLIST_HEAD(, ThreadPoolElement) head;
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/* The following variables are protected by lock. */
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static QTAILQ_HEAD(, ThreadPoolElement) request_list;
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static int cur_threads; |
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static int idle_threads; |
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static int new_threads; /* backlog of threads we need to create */ |
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static int pending_threads; /* threads created but not running yet */ |
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static int pending_cancellations; /* whether we need a cond_broadcast */ |
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static void *worker_thread(void *unused) |
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{ |
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qemu_mutex_lock(&lock); |
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pending_threads--; |
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do_spawn_thread(); |
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while (1) { |
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ThreadPoolElement *req; |
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int ret;
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do {
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idle_threads++; |
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qemu_mutex_unlock(&lock); |
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ret = qemu_sem_timedwait(&sem, 10000);
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qemu_mutex_lock(&lock); |
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idle_threads--; |
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} while (ret == -1 && !QTAILQ_EMPTY(&request_list)); |
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if (ret == -1) { |
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break;
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} |
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req = QTAILQ_FIRST(&request_list); |
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QTAILQ_REMOVE(&request_list, req, reqs); |
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req->state = THREAD_ACTIVE; |
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qemu_mutex_unlock(&lock); |
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ret = req->func(req->arg); |
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req->ret = ret; |
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/* Write ret before state. */
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smp_wmb(); |
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req->state = THREAD_DONE; |
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qemu_mutex_lock(&lock); |
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if (pending_cancellations) {
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qemu_cond_broadcast(&check_cancel); |
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} |
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event_notifier_set(¬ifier); |
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} |
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cur_threads--; |
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qemu_mutex_unlock(&lock); |
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return NULL; |
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} |
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static void do_spawn_thread(void) |
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{ |
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QemuThread t; |
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/* Runs with lock taken. */
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if (!new_threads) {
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return;
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} |
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new_threads--; |
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pending_threads++; |
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qemu_thread_create(&t, worker_thread, NULL, QEMU_THREAD_DETACHED);
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} |
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static void spawn_thread_bh_fn(void *opaque) |
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{ |
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qemu_mutex_lock(&lock); |
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do_spawn_thread(); |
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qemu_mutex_unlock(&lock); |
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} |
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static void spawn_thread(void) |
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{ |
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cur_threads++; |
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new_threads++; |
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/* If there are threads being created, they will spawn new workers, so
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* we don't spend time creating many threads in a loop holding a mutex or
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* starving the current vcpu.
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*
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* If there are no idle threads, ask the main thread to create one, so we
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* inherit the correct affinity instead of the vcpu affinity.
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*/
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if (!pending_threads) {
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qemu_bh_schedule(new_thread_bh); |
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} |
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} |
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static void event_notifier_ready(EventNotifier *notifier) |
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{ |
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ThreadPoolElement *elem, *next; |
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event_notifier_test_and_clear(notifier); |
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restart:
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QLIST_FOREACH_SAFE(elem, &head, all, next) { |
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if (elem->state != THREAD_CANCELED && elem->state != THREAD_DONE) {
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continue;
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} |
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if (elem->state == THREAD_DONE) {
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trace_thread_pool_complete(elem, elem->common.opaque, elem->ret); |
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} |
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if (elem->state == THREAD_DONE && elem->common.cb) {
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QLIST_REMOVE(elem, all); |
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/* Read state before ret. */
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smp_rmb(); |
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elem->common.cb(elem->common.opaque, elem->ret); |
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qemu_aio_release(elem); |
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goto restart;
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} else {
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/* remove the request */
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QLIST_REMOVE(elem, all); |
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qemu_aio_release(elem); |
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} |
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} |
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} |
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static int thread_pool_active(EventNotifier *notifier) |
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{ |
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return !QLIST_EMPTY(&head);
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} |
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static void thread_pool_cancel(BlockDriverAIOCB *acb) |
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{ |
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ThreadPoolElement *elem = (ThreadPoolElement *)acb; |
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trace_thread_pool_cancel(elem, elem->common.opaque); |
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qemu_mutex_lock(&lock); |
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if (elem->state == THREAD_QUEUED &&
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/* No thread has yet started working on elem. we can try to "steal"
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* the item from the worker if we can get a signal from the
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* semaphore. Because this is non-blocking, we can do it with
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* the lock taken and ensure that elem will remain THREAD_QUEUED.
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*/
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qemu_sem_timedwait(&sem, 0) == 0) { |
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QTAILQ_REMOVE(&request_list, elem, reqs); |
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elem->state = THREAD_CANCELED; |
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event_notifier_set(¬ifier); |
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} else {
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pending_cancellations++; |
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while (elem->state != THREAD_CANCELED && elem->state != THREAD_DONE) {
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qemu_cond_wait(&check_cancel, &lock); |
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} |
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pending_cancellations--; |
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} |
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qemu_mutex_unlock(&lock); |
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} |
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static const AIOCBInfo thread_pool_aiocb_info = { |
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.aiocb_size = sizeof(ThreadPoolElement),
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.cancel = thread_pool_cancel, |
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}; |
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BlockDriverAIOCB *thread_pool_submit_aio(ThreadPoolFunc *func, void *arg,
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BlockDriverCompletionFunc *cb, void *opaque)
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{ |
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ThreadPoolElement *req; |
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req = qemu_aio_get(&thread_pool_aiocb_info, NULL, cb, opaque);
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req->func = func; |
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req->arg = arg; |
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req->state = THREAD_QUEUED; |
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QLIST_INSERT_HEAD(&head, req, all); |
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trace_thread_pool_submit(req, arg); |
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qemu_mutex_lock(&lock); |
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if (idle_threads == 0 && cur_threads < max_threads) { |
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spawn_thread(); |
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} |
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QTAILQ_INSERT_TAIL(&request_list, req, reqs); |
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qemu_mutex_unlock(&lock); |
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qemu_sem_post(&sem); |
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return &req->common;
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} |
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typedef struct ThreadPoolCo { |
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Coroutine *co; |
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int ret;
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} ThreadPoolCo; |
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static void thread_pool_co_cb(void *opaque, int ret) |
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{ |
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ThreadPoolCo *co = opaque; |
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co->ret = ret; |
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qemu_coroutine_enter(co->co, NULL);
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} |
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int coroutine_fn thread_pool_submit_co(ThreadPoolFunc *func, void *arg) |
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{ |
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ThreadPoolCo tpc = { .co = qemu_coroutine_self(), .ret = -EINPROGRESS }; |
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assert(qemu_in_coroutine()); |
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thread_pool_submit_aio(func, arg, thread_pool_co_cb, &tpc); |
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qemu_coroutine_yield(); |
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return tpc.ret;
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} |
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void thread_pool_submit(ThreadPoolFunc *func, void *arg) |
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{ |
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thread_pool_submit_aio(func, arg, NULL, NULL); |
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} |
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static void thread_pool_init(void) |
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{ |
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QLIST_INIT(&head); |
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event_notifier_init(¬ifier, false);
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qemu_mutex_init(&lock); |
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qemu_cond_init(&check_cancel); |
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qemu_sem_init(&sem, 0);
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qemu_aio_set_event_notifier(¬ifier, event_notifier_ready, |
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thread_pool_active); |
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QTAILQ_INIT(&request_list); |
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new_thread_bh = qemu_bh_new(spawn_thread_bh_fn, NULL);
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} |
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block_init(thread_pool_init) |