On Fri, 02/20 17:26, Paolo Bonzini wrote:
> This is the first step in pushing down acquire/release, and will let
> rfifolock drop the contention callback feature.
>
> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> ---
> aio-posix.c | 9 +++++++++
> aio-win32.c | 8 ++++++++
> include/block/aio.h | 15 ++++++++-------
> 3 files changed, 25 insertions(+), 7 deletions(-)
>
> diff --git a/aio-posix.c b/aio-posix.c
> index 4a30b77..292ae84 100644
> --- a/aio-posix.c
> +++ b/aio-posix.c
> @@ -238,6 +238,7 @@ bool aio_poll(AioContext *ctx, bool blocking)
> bool progress;
> int64_t timeout;
>
> + aio_context_acquire(ctx);
> was_dispatching = ctx->dispatching;
> progress = false;
>
> @@ -267,7 +268,13 @@ bool aio_poll(AioContext *ctx, bool blocking)
> timeout = blocking ? aio_compute_timeout(ctx) : 0;
>
> /* wait until next event */
> + if (timeout) {
> + aio_context_release(ctx);
> + }
> ret = qemu_poll_ns((GPollFD *)pollfds, npfd, timeout);
If two threads poll concurrently on this ctx, they will get the same set of
events, is that safe? Doesn't that lead to double dispatch?
Fam
> + if (timeout) {
> + aio_context_acquire(ctx);
> + }
>
> /* if we have any readable fds, dispatch event */
> if (ret > 0) {
> @@ -285,5 +292,7 @@ bool aio_poll(AioContext *ctx, bool blocking)
> }
>
> aio_set_dispatching(ctx, was_dispatching);
> + aio_context_release(ctx);
> +
> return progress;
> }
> diff --git a/aio-win32.c b/aio-win32.c
> index e6f4ced..233d8f5 100644
> --- a/aio-win32.c
> +++ b/aio-win32.c
> @@ -283,6 +283,7 @@ bool aio_poll(AioContext *ctx, bool blocking)
> int count;
> int timeout;
>
> + aio_context_acquire(ctx);
> have_select_revents = aio_prepare(ctx);
> if (have_select_revents) {
> blocking = false;
> @@ -323,7 +324,13 @@ bool aio_poll(AioContext *ctx, bool blocking)
>
> timeout = blocking
> ? qemu_timeout_ns_to_ms(aio_compute_timeout(ctx)) : 0;
> + if (timeout) {
> + aio_context_release(ctx);
> + }
> ret = WaitForMultipleObjects(count, events, FALSE, timeout);
> + if (timeout) {
> + aio_context_acquire(ctx);
> + }
> aio_set_dispatching(ctx, true);
>
> if (first && aio_bh_poll(ctx)) {
> @@ -349,5 +356,6 @@ bool aio_poll(AioContext *ctx, bool blocking)
> progress |= timerlistgroup_run_timers(&ctx->tlg);
>
> aio_set_dispatching(ctx, was_dispatching);
> + aio_context_release(ctx);
> return progress;
> }
> diff --git a/include/block/aio.h b/include/block/aio.h
> index 499efd0..e77409d 100644
> --- a/include/block/aio.h
> +++ b/include/block/aio.h
> @@ -118,13 +118,14 @@ void aio_context_ref(AioContext *ctx);
> void aio_context_unref(AioContext *ctx);
>
> /* Take ownership of the AioContext. If the AioContext will be shared
> between
> - * threads, a thread must have ownership when calling aio_poll().
> - *
> - * Note that multiple threads calling aio_poll() means timers, BHs, and
> - * callbacks may be invoked from a different thread than they were registered
> - * from. Therefore, code must use AioContext acquire/release or use
> - * fine-grained synchronization to protect shared state if other threads will
> - * be accessing it simultaneously.
> + * threads, and a thread does not want to be interrupted, it will have to
> + * take ownership around calls to aio_poll(). Otherwise, aio_poll()
> + * automatically takes care of calling aio_context_acquire and
> + * aio_context_release.
> + *
> + * Access to timers and BHs from a thread that has not acquired AioContext
> + * is possible. Access to callbacks for now must be done while the
> AioContext
> + * is owned by the thread (FIXME).
> */
> void aio_context_acquire(AioContext *ctx);
>
> --
> 2.3.0
>
>
