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d3fa923044
This patch drops a special case where aio_poll(ctx, true) returns false instead of blocking if no file descriptors are waiting on I/O. Now it is possible to block in aio_poll() to wait for aio_notify(). This change eliminates busy waiting. bdrv_drain_all() used to rely on busy waiting to completed throttled I/O requests but this is no longer required so we can simplify aio_poll(). Note that aio_poll() still returns false when aio_notify() was used. In other words, stopping a blocking aio_poll() wait is not considered making progress. Adjust test-aio /aio/bh/callback-delete/one which assumed aio_poll(ctx, true) would immediately return false instead of blocking. Reviewed-by: Alex Bligh <alex@alex.org.uk> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
243 lines
6.2 KiB
C
243 lines
6.2 KiB
C
/*
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* QEMU aio implementation
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*
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* Copyright IBM, Corp. 2008
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*
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* Authors:
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* Anthony Liguori <aliguori@us.ibm.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2. See
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* the COPYING file in the top-level directory.
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*
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* Contributions after 2012-01-13 are licensed under the terms of the
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* GNU GPL, version 2 or (at your option) any later version.
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*/
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#include "qemu-common.h"
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#include "block/block.h"
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#include "qemu/queue.h"
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#include "qemu/sockets.h"
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struct AioHandler
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{
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GPollFD pfd;
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IOHandler *io_read;
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IOHandler *io_write;
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int deleted;
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int pollfds_idx;
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void *opaque;
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QLIST_ENTRY(AioHandler) node;
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};
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static AioHandler *find_aio_handler(AioContext *ctx, int fd)
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{
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AioHandler *node;
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QLIST_FOREACH(node, &ctx->aio_handlers, node) {
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if (node->pfd.fd == fd)
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if (!node->deleted)
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return node;
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}
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return NULL;
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}
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void aio_set_fd_handler(AioContext *ctx,
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int fd,
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IOHandler *io_read,
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IOHandler *io_write,
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void *opaque)
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{
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AioHandler *node;
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node = find_aio_handler(ctx, fd);
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/* Are we deleting the fd handler? */
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if (!io_read && !io_write) {
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if (node) {
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g_source_remove_poll(&ctx->source, &node->pfd);
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/* If the lock is held, just mark the node as deleted */
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if (ctx->walking_handlers) {
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node->deleted = 1;
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node->pfd.revents = 0;
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} else {
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/* Otherwise, delete it for real. We can't just mark it as
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* deleted because deleted nodes are only cleaned up after
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* releasing the walking_handlers lock.
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*/
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QLIST_REMOVE(node, node);
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g_free(node);
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}
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}
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} else {
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if (node == NULL) {
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/* Alloc and insert if it's not already there */
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node = g_malloc0(sizeof(AioHandler));
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node->pfd.fd = fd;
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QLIST_INSERT_HEAD(&ctx->aio_handlers, node, node);
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g_source_add_poll(&ctx->source, &node->pfd);
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}
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/* Update handler with latest information */
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node->io_read = io_read;
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node->io_write = io_write;
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node->opaque = opaque;
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node->pollfds_idx = -1;
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node->pfd.events = (io_read ? G_IO_IN | G_IO_HUP | G_IO_ERR : 0);
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node->pfd.events |= (io_write ? G_IO_OUT | G_IO_ERR : 0);
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}
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aio_notify(ctx);
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}
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void aio_set_event_notifier(AioContext *ctx,
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EventNotifier *notifier,
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EventNotifierHandler *io_read)
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{
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aio_set_fd_handler(ctx, event_notifier_get_fd(notifier),
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(IOHandler *)io_read, NULL, notifier);
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}
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bool aio_pending(AioContext *ctx)
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{
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AioHandler *node;
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QLIST_FOREACH(node, &ctx->aio_handlers, node) {
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int revents;
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revents = node->pfd.revents & node->pfd.events;
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if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read) {
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return true;
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}
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if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write) {
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return true;
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}
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}
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return false;
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}
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static bool aio_dispatch(AioContext *ctx)
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{
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AioHandler *node;
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bool progress = false;
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/*
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* We have to walk very carefully in case qemu_aio_set_fd_handler is
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* called while we're walking.
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*/
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node = QLIST_FIRST(&ctx->aio_handlers);
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while (node) {
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AioHandler *tmp;
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int revents;
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ctx->walking_handlers++;
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revents = node->pfd.revents & node->pfd.events;
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node->pfd.revents = 0;
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if (!node->deleted &&
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(revents & (G_IO_IN | G_IO_HUP | G_IO_ERR)) &&
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node->io_read) {
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node->io_read(node->opaque);
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/* aio_notify() does not count as progress */
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if (node->opaque != &ctx->notifier) {
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progress = true;
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}
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}
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if (!node->deleted &&
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(revents & (G_IO_OUT | G_IO_ERR)) &&
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node->io_write) {
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node->io_write(node->opaque);
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progress = true;
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}
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tmp = node;
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node = QLIST_NEXT(node, node);
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ctx->walking_handlers--;
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if (!ctx->walking_handlers && tmp->deleted) {
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QLIST_REMOVE(tmp, node);
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g_free(tmp);
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}
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}
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/* Run our timers */
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progress |= timerlistgroup_run_timers(&ctx->tlg);
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return progress;
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}
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bool aio_poll(AioContext *ctx, bool blocking)
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{
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AioHandler *node;
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int ret;
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bool progress;
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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 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 qemu_aio_wait 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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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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return true;
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}
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ctx->walking_handlers++;
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g_array_set_size(ctx->pollfds, 0);
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/* fill pollfds */
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QLIST_FOREACH(node, &ctx->aio_handlers, node) {
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node->pollfds_idx = -1;
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if (!node->deleted && node->pfd.events) {
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GPollFD pfd = {
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.fd = node->pfd.fd,
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.events = node->pfd.events,
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};
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node->pollfds_idx = ctx->pollfds->len;
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g_array_append_val(ctx->pollfds, pfd);
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}
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}
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ctx->walking_handlers--;
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/* wait until next event */
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ret = qemu_poll_ns((GPollFD *)ctx->pollfds->data,
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ctx->pollfds->len,
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blocking ? timerlistgroup_deadline_ns(&ctx->tlg) : 0);
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/* if we have any readable fds, dispatch event */
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if (ret > 0) {
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QLIST_FOREACH(node, &ctx->aio_handlers, node) {
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if (node->pollfds_idx != -1) {
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GPollFD *pfd = &g_array_index(ctx->pollfds, GPollFD,
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node->pollfds_idx);
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node->pfd.revents = pfd->revents;
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}
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}
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}
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/* Run dispatch even if there were no readable fds to run timers */
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if (aio_dispatch(ctx)) {
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progress = true;
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}
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return progress;
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}
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