aio: add aio_context_acquire() and aio_context_release()
It can be useful to run an AioContext from a thread which normally does
not "own" the AioContext. For example, request draining can be
implemented by acquiring the AioContext and looping aio_poll() until all
requests have been completed.
The following pattern should work:
/* Event loop thread */
while (running) {
aio_context_acquire(ctx);
aio_poll(ctx, true);
aio_context_release(ctx);
}
/* Another thread */
aio_context_acquire(ctx);
bdrv_read(bs, 0x1000, buf, 1);
aio_context_release(ctx);
This patch implements aio_context_acquire() and aio_context_release().
Note that existing aio_poll() callers do not need to worry about
acquiring and releasing - it is only needed when multiple threads will
call aio_poll() on the same AioContext.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/async.c b/async.c
index 5fb3fa6..6930185 100644
--- a/async.c
+++ b/async.c
@@ -214,6 +214,7 @@
thread_pool_free(ctx->thread_pool);
aio_set_event_notifier(ctx, &ctx->notifier, NULL);
event_notifier_cleanup(&ctx->notifier);
+ rfifolock_destroy(&ctx->lock);
qemu_mutex_destroy(&ctx->bh_lock);
g_array_free(ctx->pollfds, TRUE);
timerlistgroup_deinit(&ctx->tlg);
@@ -250,6 +251,12 @@
aio_notify(opaque);
}
+static void aio_rfifolock_cb(void *opaque)
+{
+ /* Kick owner thread in case they are blocked in aio_poll() */
+ aio_notify(opaque);
+}
+
AioContext *aio_context_new(void)
{
AioContext *ctx;
@@ -257,6 +264,7 @@
ctx->pollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
ctx->thread_pool = NULL;
qemu_mutex_init(&ctx->bh_lock);
+ rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx);
event_notifier_init(&ctx->notifier, false);
aio_set_event_notifier(ctx, &ctx->notifier,
(EventNotifierHandler *)
@@ -275,3 +283,13 @@
{
g_source_unref(&ctx->source);
}
+
+void aio_context_acquire(AioContext *ctx)
+{
+ rfifolock_lock(&ctx->lock);
+}
+
+void aio_context_release(AioContext *ctx)
+{
+ rfifolock_unlock(&ctx->lock);
+}