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 | |
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>
-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 | |||
432 | 432 | ||
433 | if(ret) | 433 | if(ret) |
434 | { | 434 | { |
435 | /* The code allows two threads to call select()/poll() at the same time. | ||
436 | * First thread just wants to read, a second thread wants to write, too. | ||
437 | * We have to make sure that we don't steal the reading thread's reply | ||
438 | * and let it get stuck in select()/poll(). | ||
439 | * So a thread may read if either: | ||
440 | * - There is no other thread that wants to read (the above situation | ||
441 | * did not occur). | ||
442 | * - It is the reading thread (above situation occurred). | ||
443 | */ | ||
444 | int may_read = c->in.reading == 1 || !count; | ||
435 | #if USE_POLL | 445 | #if USE_POLL |
436 | if((fd.revents & POLLIN) == POLLIN) | 446 | if(may_read && (fd.revents & POLLIN) == POLLIN) |
437 | #else | 447 | #else |
438 | if(FD_ISSET(c->fd, &rfds)) | 448 | if(may_read && FD_ISSET(c->fd, &rfds)) |
439 | #endif | 449 | #endif |
440 | ret = ret && _xcb_in_read(c); | 450 | ret = ret && _xcb_in_read(c); |
441 | 451 | ||