Introduce xcb_wait_for_event_until, for consuming responses in wire-order.

Signed-off-by: Jamey Sharp <jamey@minilop.net>
Reviewed-by: Josh Triplett <josh@freedesktop.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/src/xcb.h b/src/xcb.h
index 14244a7..3e61ebd 100644
--- a/src/xcb.h
+++ b/src/xcb.h
@@ -272,6 +272,41 @@ xcb_generic_event_t *xcb_wait_for_event(xcb_connection_t *c);
 xcb_generic_event_t *xcb_poll_for_event(xcb_connection_t *c);
 
 /**
+ * @brief Returns the next event or error that precedes the given request.
+ * @param c: The connection to the X server.
+ * @param request: The limiting sequence number.
+ * @return The next event from the server.
+ *
+ * Returns the next event or error with a sequence number less than or
+ * equal to the given sequence number, or returns NULL if no such event can
+ * ever arrive. Blocks until either a suitable event or error arrive, or a
+ * response arrives that proves no such event is coming, or an I/O error
+ * occurs.
+ *
+ * After processing a request, the X server sends responses in a specific
+ * order. First come any events that the request generated, then any
+ * replies for the request, then the error response if there is one. After
+ * that, the server may spontaneously send more events with the same
+ * sequence number, which are not related to that request.
+ *
+ * This function will always return events from the pre-reply phase of the
+ * specified request. It may also return events from the unrelated
+ * post-reply stream, as long as they have the same sequence number.
+ *
+ * This function is useful for callers that need to process responses in
+ * wire-order.
+ *
+ * Implementation note: You cannot currently use this function to ensure
+ * that you process responses in exactly wire-order, because depending on
+ * the sequence of calls you make and the timing of server responses,
+ * post-reply events with the same sequence number may be returned as part
+ * of the pre-reply event stream, even though they were separated by a
+ * reply or error. In practice this kind of error is unlikely to matter,
+ * but it may be fixed in the future.
+ */
+xcb_generic_event_t *xcb_wait_for_event_until(xcb_connection_t *c, unsigned int request);
+
+/**
  * @brief Return the error for a request, or NULL if none can ever arrive.
  * @param c: The connection to the X server.
  * @param cookie: The request cookie.