[Xcb-commit] 2 commits - src

[Uli Schlachter]

 src/man/.gitignore |    3 +++
 src/xcb_conn.c     |   14 ++++++++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

New commits:
commit 23911a707b8845bff52cd7853fc5d59fb0823cef
Author: Uli Schlachter <psychon at znc.in>
Date:   Mon Sep 24 22:07:51 2012 +0200

    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 at mines.edu>
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=54671
    Signed-off-by: Uli Schlachter <psychon at znc.in>

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);
 
commit c16cc5467eb0af7c5cdee16e6efaee54eb53bba6
Author: Uli Schlachter <psychon at znc.in>
Date:   Mon Sep 24 22:07:30 2012 +0200

    Add a .gitignore for src/man/
    
    Signed-off-by: Uli Schlachter <psychon at znc.in>

diff --git a/src/man/.gitignore b/src/man/.gitignore
new file mode 100644
index 0000000..b36be7f
--- /dev/null
+++ b/src/man/.gitignore
@@ -0,0 +1,3 @@
+*.3
+!xcb-examples.3
+!xcb-requests.3