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#5299 Fix blocking XREAD for streams that ran dry

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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.
This commit is contained in:
Sascha Roland 2018-08-29 17:53:47 +02:00 committed by antirez
parent d60c17cbb3
commit c1e9186f06
1 changed files with 2 additions and 2 deletions
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4
src/t_stream.c
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@ -1436,7 +1436,7 @@ void xreadCommand(client *c) {
* synchronously in case the group top item delivered is smaller * synchronously in case the group top item delivered is smaller
* than what the stream has inside. */ * than what the stream has inside. */
streamID *last = &groups[i]->last_id; 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; serve_synchronously = 1;
*gt = *last; *gt = *last;
} }
@ -1444,7 +1444,7 @@ void xreadCommand(client *c) {
} else { } else {
/* For consumers without a group, we serve synchronously if we can /* For consumers without a group, we serve synchronously if we can
* actually provide at least one item from the stream. */ * 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; serve_synchronously = 1;
} }
} }