Instrumented libraries: attempt to fix a deadlock in libxcb1.

third_party/instrumented_libraries/patches/libxcb1.precise.diff

+diff -rupN ./src/xcb_conn.c ../libxcb-1.8.1-patched/src/xcb_conn.c
+--- ./src/xcb_conn.c    2012-01-11 21:05:41.000000000 +0400
++++ ../libxcb-1.8.1-patched/src/xcb_conn.c      2014-12-10 23:37:44.432834622 +0300
+@@ -418,10 +418,20 @@ int _xcb_conn_wait(xcb_connection_t *c,
+ 
+     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);
+