sync: optimistic write

When flushing the output buffer, always assume that the socket is
writable.  Most of the time, it really is, and the select() is a waste
of time.  In case it is not, libmpdclient falls back to select().

NEWS

@@ -3,6 +3,7 @@ libmpdclient 2.1 (2009/??/??)
 * song: copy last_modified value in mpd_song_dup()
 * socket, async: use WSAGetLastError() instead of errno on WIN32
 * socket: connect in non-blocking mode
+* sync: optimistic write, reduce select() calls
 * Makefile.am: use --version-script only with GNU ld
 
 

src/sync.c

@@ -153,6 +153,9 @@ mpd_sync_flush(struct mpd_async *async, const struct timeval *tv0)
 	} else
 		tvp = NULL;
 
+	if (!mpd_async_io(async, MPD_ASYNC_EVENT_WRITE))
+		return false;
+
 	while (true) {
 		enum mpd_async_event events = mpd_async_events(async);
 		if ((events & MPD_ASYNC_EVENT_WRITE) == 0)