1 files changed, 343 insertions, 0 deletions

diff --git a/qemu/thread-pool.c b/qemu/thread-pool.c
new file mode 100644
index 000000000..ac909f498
--- /dev/null
+++ b/qemu/thread-pool.c
@@ -0,0 +1,343 @@
+/*
+ * 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/thread-pool.h"
+#include "qemu/main-loop.h"
+
+static void do_spawn_thread(ThreadPool *pool);
+
+typedef struct ThreadPoolElement ThreadPoolElement;
+
+enum ThreadState {
+    THREAD_QUEUED,
+    THREAD_ACTIVE,
+    THREAD_DONE,
+};
+
+struct ThreadPoolElement {
+    BlockAIOCB common;
+    ThreadPool *pool;
+    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;
+};
+
+struct ThreadPool {
+    AioContext *ctx;
+    QEMUBH *completion_bh;
+    QemuMutex lock;
+    QemuCond worker_stopped;
+    QemuSemaphore sem;
+    int max_threads;
+    QEMUBH *new_thread_bh;
+
+    /* The following variables are only accessed from one AioContext. */
+    QLIST_HEAD(, ThreadPoolElement) head;
+
+    /* The following variables are protected by lock.  */
+    QTAILQ_HEAD(, ThreadPoolElement) request_list;
+    int cur_threads;
+    int idle_threads;
+    int new_threads;     /* backlog of threads we need to create */
+    int pending_threads; /* threads created but not running yet */
+    bool stopping;
+};
+
+static void *worker_thread(void *opaque)
+{
+    ThreadPool *pool = opaque;
+
+    qemu_mutex_lock(&pool->lock);
+    pool->pending_threads--;
+    do_spawn_thread(pool);
+
+    while (!pool->stopping) {
+        ThreadPoolElement *req;
+        int ret;
+
+        do {
+            pool->idle_threads++;
+            qemu_mutex_unlock(&pool->lock);
+            ret = qemu_sem_timedwait(&pool->sem, 10000);
+            qemu_mutex_lock(&pool->lock);
+            pool->idle_threads--;
+        } while (ret == -1 && !QTAILQ_EMPTY(&pool->request_list));
+        if (ret == -1 || pool->stopping) {
+            break;
+        }
+
+        req = QTAILQ_FIRST(&pool->request_list);
+        QTAILQ_REMOVE(&pool->request_list, req, reqs);
+        req->state = THREAD_ACTIVE;
+        qemu_mutex_unlock(&pool->lock);
+
+        ret = req->func(req->arg);
+
+        req->ret = ret;
+        /* Write ret before state.  */
+        smp_wmb();
+        req->state = THREAD_DONE;
+
+        qemu_mutex_lock(&pool->lock);
+
+        qemu_bh_schedule(pool->completion_bh);
+    }
+
+    pool->cur_threads--;
+    qemu_cond_signal(&pool->worker_stopped);
+    qemu_mutex_unlock(&pool->lock);
+    return NULL;
+}
+
+static void do_spawn_thread(ThreadPool *pool)
+{
+    QemuThread t;
+
+    /* Runs with lock taken.  */
+    if (!pool->new_threads) {
+        return;
+    }
+
+    pool->new_threads--;
+    pool->pending_threads++;
+
+    qemu_thread_create(&t, "worker", worker_thread, pool, QEMU_THREAD_DETACHED);
+}
+
+static void spawn_thread_bh_fn(void *opaque)
+{
+    ThreadPool *pool = opaque;
+
+    qemu_mutex_lock(&pool->lock);
+    do_spawn_thread(pool);
+    qemu_mutex_unlock(&pool->lock);
+}
+
+static void spawn_thread(ThreadPool *pool)
+{
+    pool->cur_threads++;
+    pool->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 (!pool->pending_threads) {
+        qemu_bh_schedule(pool->new_thread_bh);
+    }
+}
+
+static void thread_pool_completion_bh(void *opaque)
+{
+    ThreadPool *pool = opaque;
+    ThreadPoolElement *elem, *next;
+
+restart:
+    QLIST_FOREACH_SAFE(elem, &pool->head, all, next) {
+        if (elem->state != THREAD_DONE) {
+            continue;
+        }
+
+        trace_thread_pool_complete(pool, elem, elem->common.opaque,
+                                   elem->ret);
+        QLIST_REMOVE(elem, all);
+
+        if (elem->common.cb) {
+            /* Read state before ret.  */
+            smp_rmb();
+
+            /* Schedule ourselves in case elem->common.cb() calls aio_poll() to
+             * wait for another request that completed at the same time.
+             */
+            qemu_bh_schedule(pool->completion_bh);
+
+            elem->common.cb(elem->common.opaque, elem->ret);
+            qemu_aio_unref(elem);
+            goto restart;
+        } else {
+            qemu_aio_unref(elem);
+        }
+    }
+}
+
+static void thread_pool_cancel(BlockAIOCB *acb)
+{
+    ThreadPoolElement *elem = (ThreadPoolElement *)acb;
+    ThreadPool *pool = elem->pool;
+
+    trace_thread_pool_cancel(elem, elem->common.opaque);
+
+    qemu_mutex_lock(&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) {
+        QTAILQ_REMOVE(&pool->request_list, elem, reqs);
+        qemu_bh_schedule(pool->completion_bh);
+
+        elem->state = THREAD_DONE;
+        elem->ret = -ECANCELED;
+    }
+
+    qemu_mutex_unlock(&pool->lock);
+}
+
+static AioContext *thread_pool_get_aio_context(BlockAIOCB *acb)
+{
+    ThreadPoolElement *elem = (ThreadPoolElement *)acb;
+    ThreadPool *pool = elem->pool;
+    return pool->ctx;
+}
+
+static const AIOCBInfo thread_pool_aiocb_info = {
+    .aiocb_size         = sizeof(ThreadPoolElement),
+    .cancel_async       = thread_pool_cancel,
+    .get_aio_context    = thread_pool_get_aio_context,
+};
+
+BlockAIOCB *thread_pool_submit_aio(ThreadPool *pool,
+        ThreadPoolFunc *func, void *arg,
+        BlockCompletionFunc *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;
+    req->pool = pool;
+
+    QLIST_INSERT_HEAD(&pool->head, req, all);
+
+    trace_thread_pool_submit(pool, req, arg);
+
+    qemu_mutex_lock(&pool->lock);
+    if (pool->idle_threads == 0 && pool->cur_threads < pool->max_threads) {
+        spawn_thread(pool);
+    }
+    QTAILQ_INSERT_TAIL(&pool->request_list, req, reqs);
+    qemu_mutex_unlock(&pool->lock);
+    qemu_sem_post(&pool->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(ThreadPool *pool, ThreadPoolFunc *func,
+                                       void *arg)
+{
+    ThreadPoolCo tpc = { .co = qemu_coroutine_self(), .ret = -EINPROGRESS };
+    assert(qemu_in_coroutine());
+    thread_pool_submit_aio(pool, func, arg, thread_pool_co_cb, &tpc);
+    qemu_coroutine_yield();
+    return tpc.ret;
+}
+
+void thread_pool_submit(ThreadPool *pool, ThreadPoolFunc *func, void *arg)
+{
+    thread_pool_submit_aio(pool, func, arg, NULL, NULL);
+}
+
+static void thread_pool_init_one(ThreadPool *pool, AioContext *ctx)
+{
+    if (!ctx) {
+        ctx = qemu_get_aio_context();
+    }
+
+    memset(pool, 0, sizeof(*pool));
+    pool->ctx = 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);
+    pool->max_threads = 64;
+    pool->new_thread_bh = aio_bh_new(ctx, spawn_thread_bh_fn, pool);
+
+    QLIST_INIT(&pool->head);
+    QTAILQ_INIT(&pool->request_list);
+}
+
+ThreadPool *thread_pool_new(AioContext *ctx)
+{
+    ThreadPool *pool = g_new(ThreadPool, 1);
+    thread_pool_init_one(pool, ctx);
+    return pool;
+}
+
+void thread_pool_free(ThreadPool *pool)
+{
+    if (!pool) {
+        return;
+    }
+
+    assert(QLIST_EMPTY(&pool->head));
+
+    qemu_mutex_lock(&pool->lock);
+
+    /* Stop new threads from spawning */
+    qemu_bh_delete(pool->new_thread_bh);
+    pool->cur_threads -= pool->new_threads;
+    pool->new_threads = 0;
+
+    /* Wait for worker threads to terminate */
+    pool->stopping = true;
+    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->worker_stopped);
+    qemu_mutex_destroy(&pool->lock);
+    g_free(pool);
+}