From c1e9186f069e0b3aa1507e0e86a16d5001ea5420 Mon Sep 17 00:00:00 2001 From: Sascha Roland Date: Wed, 29 Aug 2018 17:53:47 +0200 Subject: [PATCH] #5299 Fix blocking XREAD for streams that ran dry The conclusion, that a xread request can be answered syncronously in case that the stream's last_id is larger than the passed last-received-id parameter, assumes, that there must be entries present, which could be returned immediately. This assumption fails for empty streams that actually contained some entries which got removed by xdel, ... . As result, the client is answered synchronously with an empty result, instead of blocking for new entries to arrive. An additional check for a non-empty stream is required. --- src/t_stream.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/src/t_stream.c b/src/t_stream.c index 77fbf464..40e0c84b 100644 --- a/src/t_stream.c +++ b/src/t_stream.c @@ -1436,7 +1436,7 @@ void xreadCommand(client *c) { * synchronously in case the group top item delivered is smaller * than what the stream has inside. */ streamID *last = &groups[i]->last_id; - if (streamCompareID(&s->last_id, last) > 0) { + if (s->length && (streamCompareID(&s->last_id, last) > 0)) { serve_synchronously = 1; *gt = *last; } @@ -1444,7 +1444,7 @@ void xreadCommand(client *c) { } else { /* For consumers without a group, we serve synchronously if we can * actually provide at least one item from the stream. */ - if (streamCompareID(&s->last_id, gt) > 0) { + if (s->length && (streamCompareID(&s->last_id, gt) > 0)) { serve_synchronously = 1; } }