AioContext: export and use aio_dispatch
So far, aio_poll's scheme was dispatch/poll/dispatch, where the first dispatch phase was used only in the GSource case in order to avoid a blocking poll. Earlier patches changed it to dispatch/prepare/poll/dispatch, where prepare is aio_compute_timeout. By making aio_dispatch public, we can remove the first dispatch phase altogether, so that both aio_poll and the GSource use the same prepare/poll/dispatch scheme. This patch breaks the invariant that aio_poll(..., true) will not block the first time it returns false. This used to be fundamental for qemu_aio_flush's implementation as "while (qemu_aio_wait()) {}" but no code in QEMU relies on this invariant anymore. The return value of aio_poll() is now comparable with that of g_main_context_iteration. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
parent
3672fa5083
commit
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55
aio-posix.c
55
aio-posix.c
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@ -119,11 +119,20 @@ bool aio_pending(AioContext *ctx)
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return false;
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return false;
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}
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}
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static bool aio_dispatch(AioContext *ctx)
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bool aio_dispatch(AioContext *ctx)
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{
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{
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AioHandler *node;
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AioHandler *node;
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bool progress = false;
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bool progress = false;
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/*
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* If there are callbacks left that have been queued, we need to call them.
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* Do not call select in this case, because it is possible that the caller
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* does not need a complete flush (as is the case for aio_poll loops).
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*/
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if (aio_bh_poll(ctx)) {
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progress = true;
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}
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/*
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/*
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* We have to walk very carefully in case aio_set_fd_handler is
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* We have to walk very carefully in case aio_set_fd_handler is
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* called while we're walking.
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* called while we're walking.
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@ -184,22 +193,9 @@ bool aio_poll(AioContext *ctx, bool blocking)
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/* aio_notify can avoid the expensive event_notifier_set if
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/* aio_notify can avoid the expensive event_notifier_set if
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* everything (file descriptors, bottom halves, timers) will
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* everything (file descriptors, bottom halves, timers) will
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* be re-evaluated before the next blocking poll(). This happens
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* be re-evaluated before the next blocking poll(). This is
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* in two cases:
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* already true when aio_poll is called with blocking == false;
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*
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* if blocking == true, it is only true after poll() returns.
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* 1) when aio_poll is called with blocking == false
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*
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* 2) when we are called after poll(). If we are called before
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* poll(), bottom halves will not be re-evaluated and we need
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* aio_notify() if blocking == true.
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*
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* The first aio_dispatch() only does something when AioContext is
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* running as a GSource, and in that case aio_poll is used only
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* with blocking == false, so this optimization is already quite
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* effective. However, the code is ugly and should be restructured
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* to have a single aio_dispatch() call. To do this, we need to
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* reorganize aio_poll into a prepare/poll/dispatch model like
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* glib's.
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*
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*
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* If we're in a nested event loop, ctx->dispatching might be true.
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* If we're in a nested event loop, ctx->dispatching might be true.
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* In that case we can restore it just before returning, but we
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* In that case we can restore it just before returning, but we
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@ -207,26 +203,6 @@ bool aio_poll(AioContext *ctx, bool blocking)
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*/
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*/
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aio_set_dispatching(ctx, !blocking);
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aio_set_dispatching(ctx, !blocking);
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/*
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* If there are callbacks left that have been queued, we need to call them.
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* Do not call select in this case, because it is possible that the caller
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* does not need a complete flush (as is the case for aio_poll loops).
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*/
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if (aio_bh_poll(ctx)) {
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blocking = false;
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progress = true;
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}
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/* Re-evaluate condition (1) above. */
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aio_set_dispatching(ctx, !blocking);
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if (aio_dispatch(ctx)) {
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progress = true;
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}
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if (progress && !blocking) {
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goto out;
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}
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ctx->walking_handlers++;
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ctx->walking_handlers++;
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g_array_set_size(ctx->pollfds, 0);
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g_array_set_size(ctx->pollfds, 0);
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@ -264,15 +240,10 @@ bool aio_poll(AioContext *ctx, bool blocking)
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/* Run dispatch even if there were no readable fds to run timers */
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/* Run dispatch even if there were no readable fds to run timers */
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aio_set_dispatching(ctx, true);
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aio_set_dispatching(ctx, true);
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if (aio_bh_poll(ctx)) {
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progress = true;
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}
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if (aio_dispatch(ctx)) {
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if (aio_dispatch(ctx)) {
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progress = true;
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progress = true;
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}
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}
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out:
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aio_set_dispatching(ctx, was_dispatching);
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aio_set_dispatching(ctx, was_dispatching);
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return progress;
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return progress;
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}
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}
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29
aio-win32.c
29
aio-win32.c
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@ -130,11 +130,12 @@ static bool aio_dispatch_handlers(AioContext *ctx, HANDLE event)
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return progress;
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return progress;
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}
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}
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static bool aio_dispatch(AioContext *ctx)
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bool aio_dispatch(AioContext *ctx)
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{
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{
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bool progress;
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bool progress;
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progress = aio_dispatch_handlers(ctx, INVALID_HANDLE_VALUE);
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progress = aio_bh_poll(ctx);
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progress |= aio_dispatch_handlers(ctx, INVALID_HANDLE_VALUE);
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progress |= timerlistgroup_run_timers(&ctx->tlg);
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progress |= timerlistgroup_run_timers(&ctx->tlg);
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return progress;
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return progress;
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}
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}
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@ -149,23 +150,6 @@ bool aio_poll(AioContext *ctx, bool blocking)
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progress = false;
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progress = false;
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/*
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* If there are callbacks left that have been queued, we need to call then.
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* Do not call select in this case, because it is possible that the caller
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* does not need a complete flush (as is the case for aio_poll loops).
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*/
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if (aio_bh_poll(ctx)) {
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blocking = false;
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progress = true;
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}
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/* Dispatch any pending callbacks from the GSource. */
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progress |= aio_dispatch(ctx);
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if (progress && !blocking) {
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return true;
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}
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ctx->walking_handlers++;
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ctx->walking_handlers++;
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/* fill fd sets */
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/* fill fd sets */
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@ -205,14 +189,7 @@ bool aio_poll(AioContext *ctx, bool blocking)
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events[ret - WAIT_OBJECT_0] = events[--count];
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events[ret - WAIT_OBJECT_0] = events[--count];
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}
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}
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if (blocking) {
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/* Run the timers a second time. We do this because otherwise aio_wait
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* will not note progress - and will stop a drain early - if we have
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* a timer that was not ready to run entering g_poll but is ready
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* after g_poll. This will only do anything if a timer has expired.
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*/
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progress |= timerlistgroup_run_timers(&ctx->tlg);
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progress |= timerlistgroup_run_timers(&ctx->tlg);
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}
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return progress;
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return progress;
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}
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}
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2
async.c
2
async.c
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@ -213,7 +213,7 @@ aio_ctx_dispatch(GSource *source,
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AioContext *ctx = (AioContext *) source;
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AioContext *ctx = (AioContext *) source;
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assert(callback == NULL);
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assert(callback == NULL);
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aio_poll(ctx, false);
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aio_dispatch(ctx);
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return true;
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return true;
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}
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}
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@ -211,6 +211,12 @@ void qemu_bh_delete(QEMUBH *bh);
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*/
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*/
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bool aio_pending(AioContext *ctx);
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bool aio_pending(AioContext *ctx);
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/* Dispatch any pending callbacks from the GSource attached to the AioContext.
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*
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* This is used internally in the implementation of the GSource.
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*/
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bool aio_dispatch(AioContext *ctx);
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/* Progress in completing AIO work to occur. This can issue new pending
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/* Progress in completing AIO work to occur. This can issue new pending
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* aio as a result of executing I/O completion or bh callbacks.
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* aio as a result of executing I/O completion or bh callbacks.
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*
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*
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