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http://dev.sourcefabric.org/browse/LS-489?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17828#action_17828
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David Baelde commented on LS-489:
---------------------------------
I finally reproduced with enough information to understand the bug. In itself
it's very simple: currently in Request_source.queued, it is possible to expire
a request twice, which removes its duration twice from the queue length. (By
the way, we could have observed the bug by seeing the negative lengths in log
level 4 of queued sources: they appear quickly.)
It's interesting to see what happens after that. You end up with 1 expired
request and a duration of -X (X being the default duration: 1323000 in ticks),
so 2 requests need to be prepared to get a queue of length X (at which point
the expired request is dropped). If we double-expired these two, we have 2
expired requests and a length of -3X. And so on and so forth. After several
iterations I see my queue length dropping to -337365000, then it doubles again
to -676053000 -- between those peaks, it gradually comes back to 0. If we
double again we get... 795377648. In my test I got a queue length of 794054648,
but the main point is that now we have a high length, and the requests in the
queue are all expired. So they are played one by one but the length is not
decreased. Eventually, we have 0 requests and a high length, so no prefetching
is done: the playlist is stuck.
The fix is very easy, but I'm waiting a little bit to close this issue, for
various reasons:
* The bug would not have occurred without double-loading of playlists, which I
observe in the logs even after the recent fix in that area.
* The freeze would not have happened if queue_length was in seconds instead of
ticks. It would be a good idea to change, but for that reason it's tempting to
keep it.
* There could be more info in the logs, such as the number of requests
(expired or not) in the queue, and some sanity checks (eg. length>=0).
> Playlist (queued request source) seems stuck
> --------------------------------------------
>
> Key: LS-489
> URL: http://dev.sourcefabric.org/browse/LS-489
> Project: Liquidsoap
> Issue Type: Bug
> Reporter: David Baelde
> Assignee: David Baelde
> Priority: Blocker
> Fix For: 1.0 beta
>
>
> On my private radio station (friends.ogg) I have a playlist in a fallback
> with a failsafe song, and from time to time the radio just loops on the
> default song, sometimes for days. The playlist reloads fine (automatically or
> manually) so there doesn't seem to be a deadlock, but somehow it remains
> unavailable for streaming.
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