diff options
| author | Uli Schlachter <psychon@znc.in> | 2012-09-24 22:07:51 +0200 |
|---|---|---|
| committer | Uli Schlachter <psychon@znc.in> | 2012-09-30 10:10:18 +0200 |
| commit | 23911a707b8845bff52cd7853fc5d59fb0823cef (patch) | |
| tree | f5a09a62d8a8d5491df9069f6a709896c98d673f /src | |
| parent | c16cc5467eb0af7c5cdee16e6efaee54eb53bba6 (diff) | |
Fix a multi-thread deadlock
This fixes a deadlock which was seen in-the-wild with wine.
It could happen that two threads tried to read from the socket at the same time
and one of the thread got stuck inside of poll()/select().
The fix works by making sure that the writing thread doesn't steal the reading
thread's reply.
Debugged-by: Erich Hoover <ehoover@mines.edu>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=54671
Signed-off-by: Uli Schlachter <psychon@znc.in>
Diffstat (limited to 'src')
| -rw-r--r-- | src/xcb_conn.c | 14 |
1 files changed, 12 insertions, 2 deletions
diff --git a/src/xcb_conn.c b/src/xcb_conn.c index e01d566..6a7a806 100644 --- a/src/xcb_conn.c +++ b/src/xcb_conn.c @@ -432,10 +432,20 @@ int _xcb_conn_wait(xcb_connection_t *c, pthread_cond_t *cond, struct iovec **vec if(ret) { + /* The code allows two threads to call select()/poll() at the same time. + * First thread just wants to read, a second thread wants to write, too. + * We have to make sure that we don't steal the reading thread's reply + * and let it get stuck in select()/poll(). + * So a thread may read if either: + * - There is no other thread that wants to read (the above situation + * did not occur). + * - It is the reading thread (above situation occurred). + */ + int may_read = c->in.reading == 1 || !count; #if USE_POLL - if((fd.revents & POLLIN) == POLLIN) + if(may_read && (fd.revents & POLLIN) == POLLIN) #else - if(FD_ISSET(c->fd, &rfds)) + if(may_read && FD_ISSET(c->fd, &rfds)) #endif ret = ret && _xcb_in_read(c); |