Revert "fix deadlock with xcb_take_socket/return_socket v3"

This reverts commit 9ae84ad187.

After this patch was merged, there were complaints about it not being a good
idea. Revert this for now until we can agree on this.

References: http://lists.freedesktop.org/archives/xcb/2013-June/008340.html
Signed-off-by: Uli Schlachter <psychon@znc.in>

Conflicts:
	src/xcbint.h

src/xcb_out.c

@@ -86,24 +86,21 @@ static void send_sync(xcb_connection_t *c)
 
 static void get_socket_back(xcb_connection_t *c)
 {
-    while (c->out.return_socket) {
-        /* we are about to release the lock,
-           so make a copy of the current status */
-        xcb_return_socket_func_t return_socket = c->out.return_socket;
-        void *socket_closure = c->out.socket_closure;
-        int socket_seq = c->out.socket_seq;
+    while(c->out.return_socket && c->out.socket_moving)
+        pthread_cond_wait(&c->out.socket_cond, &c->iolock);
+    if(!c->out.return_socket)
+        return;
 
-        pthread_mutex_unlock(&c->iolock);
-        return_socket(socket_closure);
-        pthread_mutex_lock(&c->iolock);
+    c->out.socket_moving = 1;
+    pthread_mutex_unlock(&c->iolock);
+    c->out.return_socket(c->out.socket_closure);
+    pthread_mutex_lock(&c->iolock);
+    c->out.socket_moving = 0;
 
-        /* make sure nobody else has acquired the socket */
-        if (socket_seq == c->out.socket_seq) {
-            c->out.return_socket = 0;
-            c->out.socket_closure = 0;
-            _xcb_in_replies_done(c);
-        }
-    }
+    pthread_cond_broadcast(&c->out.socket_cond);
+    c->out.return_socket = 0;
+    c->out.socket_closure = 0;
+    _xcb_in_replies_done(c);
 }
 
 /* Public interface */
@@ -299,7 +296,6 @@ int xcb_take_socket(xcb_connection_t *c, void (*return_socket)(void *closure), v
     {
         c->out.return_socket = return_socket;
         c->out.socket_closure = closure;
-        ++c->out.socket_seq;
         if(flags)
             _xcb_in_expect_reply(c, c->out.request, WORKAROUND_EXTERNAL_SOCKET_OWNER, flags);
         assert(c->out.request == c->out.request_written);
@@ -336,9 +332,11 @@ int xcb_flush(xcb_connection_t *c)
 
 int _xcb_out_init(_xcb_out *out)
 {
+    if(pthread_cond_init(&out->socket_cond, 0))
+        return 0;
     out->return_socket = 0;
     out->socket_closure = 0;
-    out->socket_seq = 0;
+    out->socket_moving = 0;
 
     if(pthread_cond_init(&out->cond, 0))
         return 0;

src/xcbext.h

@@ -69,7 +69,6 @@ void xcb_send_fd(xcb_connection_t *c, int fd);
  * callback which XCB can call when it wants the write side of the
  * socket back to make a request. This callback synchronizes with the
  * external socket owner and flushes any output queues if appropriate.
- * The callback might be called from different threads at the same time.
  * If you are sending requests which won't cause a reply, please note the
  * comment for xcb_writev which explains some sequence number wrap issues.
  * */

src/xcbint.h

@@ -79,8 +79,6 @@ void *_xcb_map_remove(_xcb_map *q, unsigned int key);
 
 /* xcb_out.c */
 
-typedef void (*xcb_return_socket_func_t)(void *closure);
-
 #if HAVE_SENDMSG
 #define XCB_MAX_PASS_FD	16
 
@@ -95,9 +93,10 @@ typedef struct _xcb_out {
     pthread_cond_t cond;
     int writing;
 
-    xcb_return_socket_func_t return_socket;
+    pthread_cond_t socket_cond;
+    void (*return_socket)(void *closure);
     void *socket_closure;
-    unsigned int socket_seq;
+    int socket_moving;
 
     char queue[XCB_QUEUE_BUFFER_SIZE];
     int queue_len;