Commit 171e0bda authored by Marek Chalupa's avatar Marek Chalupa Committed by Pekka Paalanen

tests: test if thread can block on error

wl_display_read_events() can make a thread wait until some other thread
ends reading. Normally it wakes up all threads after the reading is
done. But there's a place when it does not get to waking up the threads
- when an error occurs. This test reveals bug that can block programs.

If a thread is waiting in wl_display_read_events() and another thread
calls wl_display_read_events and the reading fails,
then the sleeping thread is not woken up. This is because
display_handle_error is using old pthread_cond instead of new
display->reader_cond, that was added along with wl_display_read_events().
Reviewed-by: Pekka Paalanen's avatarPekka Paalanen <>
parent 47208d2a
......@@ -31,6 +31,7 @@
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <pthread.h>
#include "wayland-private.h"
#include "wayland-server.h"
......@@ -323,3 +324,92 @@ TEST(post_nomem_tst)
static void
register_reading(struct wl_display *display)
while(wl_display_prepare_read(display) != 0 && errno == EAGAIN)
assert(wl_display_dispatch_pending(display) >= 0);
assert(wl_display_flush(display) >= 0);
static void *
thread_read_error(void *data)
struct client *c = data;
* Calling the read right now will block this thread
* until the other thread will read the data.
* However, after invoking an error, this
* thread should be woken up or it will block indefinitely.
c->display_stopped = 1;
assert(wl_display_read_events(c->wl_display) == 0);
/* test posting an error in multi-threaded environment. */
static void
struct client *c = client_connect();
pthread_t thread;
/* register read intention */
/* use this var as an indicator that thread is sleeping */
c->display_stopped = 0;
/* create new thread that will register its intention too */
assert(pthread_create(&thread, NULL, thread_read_error, c) == 0);
/* make sure thread is sleeping. It's a little bit racy
* (setting display_stopped to 1 and calling wl_display_read_events)
* so call usleep once again after the loop ends - it should
* be sufficient... */
while (c->display_stopped == 0)
/* so now we have sleeping thread waiting for a pthread_cond signal.
* The main thread must call wl_display_read_events().
* If this call fails, then it won't call broadcast at the
* end of the function and the sleeping thread will block indefinitely.
* Make the call fail and watch if libwayland will unblock the thread! */
/* create error on fd, so that wl_display_read_events will fail.
* The same can happen when server hangs up */
/* this read events will fail and will
* post an error that should wake the sleeping thread
* and dispatch the incoming events */
assert(wl_display_read_events(c->wl_display) == -1);
/* kill test in 3 seconds. This should be enough time for the
* thread to exit if it's not blocking. If everything is OK, than
* the thread was woken up and the test will end before the SIGALRM */
pthread_join(thread, NULL);
wl_proxy_destroy((struct wl_proxy *) c->tc);
struct display *d = display_create();
client_create(d, threading_post_err);
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