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aio: add aio_context_acquire() and aio_context_release()

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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>
This commit is contained in:
Stefan Hajnoczi
2014-03-03 11:30:04 +01:00
parent 2da61b671e
commit 98563fc3ec
3 changed files with 95 additions and 0 deletions
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18
async.c
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@@ -214,6 +214,7 @@ aio_ctx_finalize(GSource *source)
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 @@ static void aio_timerlist_notify(void *opaque)
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 @@ AioContext *aio_context_new(void)
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 @@ void aio_context_unref(AioContext *ctx)
{
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);
}