From 0b8da0ce5027127e25b0c72e70201a4fcb92a09b Mon Sep 17 00:00:00 2001
From: David Herrmann <dh.herrmann@googlemail.com>
Date: Sat, 19 May 2012 13:47:55 +0200
Subject: [PATCH] eloop: dynamically reallocate dispatch cache

We do not maintain event caches so we must make sure that every event
source gets dispatched. If we call epoll_wait() and our buffer gets
filled everytime, then there might be an event source that does not get
dispatched because it is always above the buffer range. Therefore, we now
dynamically increase the cache size when it once gets filled up.

This gets critical if we handle thousands of clients or fds, however, our
use case is limited to some system resources and hence does not suffer
here.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
---
 src/eloop.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 46 insertions(+), 14 deletions(-)

diff --git a/src/eloop.c b/src/eloop.c
index dda5e22..691ede0 100644
--- a/src/eloop.c
+++ b/src/eloop.c
@@ -75,6 +75,7 @@ struct ev_eloop {
 	struct kmscon_dlist sig_list;
 	struct kmscon_hook *idlers;
 
+	bool dispatching;
 	struct epoll_event *cur_fds;
 	size_t cur_fds_cnt;
 	bool exit;
@@ -362,9 +363,17 @@ int ev_eloop_new(struct ev_eloop **out)
 	loop->ref = 1;
 	kmscon_dlist_init(&loop->sig_list);
 
+	loop->cur_fds_cnt = 32;
+	loop->cur_fds = malloc(sizeof(struct epoll_event) *
+			       loop->cur_fds_cnt);
+	if (!loop->cur_fds) {
+		ret = -ENOMEM;
+		goto err_free;
+	}
+
 	ret = kmscon_hook_new(&loop->idlers);
 	if (ret)
-		goto err_free;
+		goto err_fds;
 
 	loop->efd = epoll_create1(EPOLL_CLOEXEC);
 	if (loop->efd < 0) {
@@ -390,6 +399,8 @@ err_close:
 	close(loop->efd);
 err_idlers:
 	kmscon_hook_free(loop->idlers);
+err_fds:
+	free(loop->cur_fds);
 err_free:
 	free(loop);
 	return ret;
@@ -423,6 +434,7 @@ void ev_eloop_unref(struct ev_eloop *loop)
 	ev_fd_unref(loop->fd);
 	close(loop->efd);
 	kmscon_hook_free(loop->idlers);
+	free(loop->cur_fds);
 	free(loop);
 }
 
@@ -433,33 +445,40 @@ void ev_eloop_flush_fd(struct ev_eloop *loop, struct ev_fd *fd)
 	if (!loop || !fd)
 		return;
 
-	for (i = 0; i < loop->cur_fds_cnt; ++i) {
-		if (loop->cur_fds[i].data.ptr == fd)
-			loop->cur_fds[i].data.ptr = NULL;
+	if (loop->dispatching) {
+		for (i = 0; i < loop->cur_fds_cnt; ++i) {
+			if (loop->cur_fds[i].data.ptr == fd)
+				loop->cur_fds[i].data.ptr = NULL;
+		}
 	}
 }
 
 int ev_eloop_dispatch(struct ev_eloop *loop, int timeout)
 {
-	struct epoll_event ep[32];
+	struct epoll_event *ep;
 	struct ev_fd *fd;
 	int i, count, mask;
 
 	if (!loop || loop->exit)
 		return -EINVAL;
 
-	count = epoll_wait(loop->efd, ep, 32, timeout);
+	count = epoll_wait(loop->efd,
+			   loop->cur_fds,
+			   loop->cur_fds_cnt,
+			   timeout);
 	if (count < 0) {
 		if (errno == EINTR) {
-			count = 0;
+			return 0;
 		} else {
 			log_warn("epoll_wait dispatching failed: %m");
 			return -errno;
 		}
+	} else if (count > loop->cur_fds_cnt) {
+		count = loop->cur_fds_cnt;
 	}
 
-	loop->cur_fds = ep;
-	loop->cur_fds_cnt = count;
+	ep = loop->cur_fds;
+	loop->dispatching = true;
 
 	for (i = 0; i < count; ++i) {
 		fd = ep[i].data.ptr;
@@ -481,8 +500,19 @@ int ev_eloop_dispatch(struct ev_eloop *loop, int timeout)
 		fd->cb(fd, mask, fd->data);
 	}
 
-	loop->cur_fds = NULL;
-	loop->cur_fds_cnt = 0;
+	loop->dispatching = false;
+
+	if (count == loop->cur_fds_cnt) {
+		ep = realloc(loop->cur_fds, sizeof(struct epoll_event) *
+			     loop->cur_fds_cnt * 2);
+		if (!ep) {
+			log_warning("cannot reallocate dispatch cache to size %u",
+				    loop->cur_fds_cnt * 2);
+		} else {
+			loop->cur_fds = ep;
+			loop->cur_fds_cnt *= 2;
+		}
+	}
 
 	return 0;
 }
@@ -844,9 +874,11 @@ void ev_eloop_rm_fd(struct ev_fd *fd)
 	 * If we are currently dispatching events, we need to remove ourself
 	 * from the temporary event list.
 	 */
-	for (i = 0; i < loop->cur_fds_cnt; ++i) {
-		if (fd == loop->cur_fds[i].data.ptr)
-			loop->cur_fds[i].data.ptr = NULL;
+	if (loop->dispatching) {
+		for (i = 0; i < loop->cur_fds_cnt; ++i) {
+			if (fd == loop->cur_fds[i].data.ptr)
+				loop->cur_fds[i].data.ptr = NULL;
+		}
 	}
 
 	fd->loop = NULL;
-- 
2.7.4