bool progress = false;
/*
- * We have to walk very carefully in case qemu_aio_set_fd_handler is
+ * We have to walk very carefully in case aio_set_fd_handler is
* called while we're walking.
*/
node = QLIST_FIRST(&ctx->aio_handlers);
bool aio_poll(AioContext *ctx, bool blocking)
{
AioHandler *node;
+ bool was_dispatching;
int ret;
bool progress;
+ was_dispatching = ctx->dispatching;
progress = false;
+ /* 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.
+ *
+ * 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
+ * have to clear it now.
+ */
+ 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 qemu_aio_wait loops).
+ * 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) {
- return true;
+ goto out;
}
ctx->walking_handlers++;
ctx->walking_handlers--;
- /* early return if we only have the aio_notify() fd */
- if (ctx->pollfds->len == 1) {
- return progress;
- }
-
/* wait until next event */
ret = qemu_poll_ns((GPollFD *)ctx->pollfds->data,
ctx->pollfds->len,
}
/* Run dispatch even if there were no readable fds to run timers */
+ aio_set_dispatching(ctx, true);
if (aio_dispatch(ctx)) {
progress = true;
}
+out:
+ aio_set_dispatching(ctx, was_dispatching);
return progress;
}