bus_read invokes callback with null message to notify that it is listening on the bus

Signed-off-by: Mattias Andrée <maandree@operamail.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/bus.c b/src/bus.c
index 5875b2b..f4f62c2 100644
--- a/src/bus.c
+++ b/src/bus.c
@@ -629,6 +629,12 @@ fail:
  *                      *  0:  stop listening
  *                      *  1:  continue listening
  *                      * -1:  an error has occurred
+ *		      However, the function [`bus_read`] will invoke
+ *                    `callback` with `message` one time directly after
+ *                    it has started listening on the bus. This is to
+ *                    the the program now it can safely continue with
+ *                    any action that requires that the programs is
+ *                    listening on the port.
  * @return            0 on success, -1 on error
  */
 int
@@ -636,6 +642,11 @@ bus_read(const bus_t *bus, int (*callback)(const char *message, void *user_data)
 {
 	int r;
 	t(release_semaphore(bus, S, SEM_UNDO));
+	t(r = callback(NULL, user_data));
+	if (!r) {
+		t(acquire_semaphore(bus, S, SEM_UNDO));
+		return 0;
+	}
 	for (;;) {
 		t(release_semaphore(bus, Q, 0));
 		t(zero_semaphore(bus, Q));