From e4c7e2d12d7b1c4501ab3397218a206d4953e633 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Wed, 9 Jul 2014 11:53:05 +0200 Subject: 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 Signed-off-by: Stefan Hajnoczi --- aio-posix.c | 55 +++++++++++++------------------------------------------ 1 file changed, 13 insertions(+), 42 deletions(-) (limited to 'aio-posix.c') diff --git a/aio-posix.c b/aio-posix.c index 798a3ff532..0936b4ff9d 100644 --- a/aio-posix.c +++ b/aio-posix.c @@ -119,11 +119,20 @@ bool aio_pending(AioContext *ctx) return false; } -static bool aio_dispatch(AioContext *ctx) +bool aio_dispatch(AioContext *ctx) { AioHandler *node; bool progress = false; + /* + * If there are callbacks left that have been queued, we need to call them. + * Do not call select in this case, because it is possible that the caller + * does not need a complete flush (as is the case for aio_poll loops). + */ + if (aio_bh_poll(ctx)) { + progress = true; + } + /* * We have to walk very carefully in case aio_set_fd_handler is * called while we're walking. @@ -184,22 +193,9 @@ bool aio_poll(AioContext *ctx, bool blocking) /* aio_notify can avoid the expensive event_notifier_set if * everything (file descriptors, bottom halves, timers) will - * be re-evaluated before the next blocking poll(). This happens - * in two cases: - * - * 1) when aio_poll is called with blocking == false - * - * 2) when we are called after poll(). If we are called before - * poll(), bottom halves will not be re-evaluated and we need - * aio_notify() if blocking == true. - * - * The first aio_dispatch() only does something when AioContext is - * running as a GSource, and in that case aio_poll is used only - * with blocking == false, so this optimization is already quite - * effective. However, the code is ugly and should be restructured - * to have a single aio_dispatch() call. To do this, we need to - * reorganize aio_poll into a prepare/poll/dispatch model like - * glib's. + * be re-evaluated before the next blocking poll(). This is + * already true when aio_poll is called with blocking == false; + * if blocking == true, it is only true after poll() returns. * * If we're in a nested event loop, ctx->dispatching might be true. * In that case we can restore it just before returning, but we @@ -207,26 +203,6 @@ bool aio_poll(AioContext *ctx, bool blocking) */ aio_set_dispatching(ctx, !blocking); - /* - * If there are callbacks left that have been queued, we need to call them. - * Do not call select in this case, because it is possible that the caller - * does not need a complete flush (as is the case for aio_poll loops). - */ - if (aio_bh_poll(ctx)) { - blocking = false; - progress = true; - } - - /* Re-evaluate condition (1) above. */ - aio_set_dispatching(ctx, !blocking); - if (aio_dispatch(ctx)) { - progress = true; - } - - if (progress && !blocking) { - goto out; - } - ctx->walking_handlers++; g_array_set_size(ctx->pollfds, 0); @@ -264,15 +240,10 @@ bool aio_poll(AioContext *ctx, bool blocking) /* Run dispatch even if there were no readable fds to run timers */ aio_set_dispatching(ctx, true); - if (aio_bh_poll(ctx)) { - progress = true; - } - if (aio_dispatch(ctx)) { progress = true; } -out: aio_set_dispatching(ctx, was_dispatching); return progress; } -- cgit v1.2.1