Moves writeback to outside of lock #274
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Refactors the metric writing code of `aggregator_expire`. While we hold the lock, don't write metrics but instead accumulate them to a nul-separated buffer. After releasing the lock, write the metrics to the fd one at a time so that we can properly track `sent` and `dropped` metrics.
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The write was never supposed to block. It seems I forgot about this for the pipe. |
grobian
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Jul 19, 2017
This is an alternative to PR #274, where instead of adding another queue (that can explode) all locks are released before issuing the write. This way, should the dispatchers be busy (and the write block) further aggregation work can continue. While at it, some more locks were introduced to keep the critical sections low. Most runs under a read-lock now, and the expiry thread does its modifications in one go after it produced all aggregates. With this locking, it should be possible to run more than 1 expiry thread.
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I don't like the buffering approach because it opens up another possibility to blow up memory-wise, so I changed the aggregator instead not to hold the lock file writing, and avoid exclusive locking more than it did before. I think this should fix your deadlock. Any feedback would be much appreciated. |
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If all dispatchers are blocking on an
invlockheld byaggregator_expire, and sufficient metrics have been sent back into the system but not yet read, the system can deadlock withaggregator_expireblocking on the socket write, while the threads that could free space in the FIFO are blocking onaggregator_expire.While
aggregator_expireholds the lock, don't write metrics but instead accumulate them to a NUL-separated buffer. After releasing the lock, write the metrics to the fd one at a time so that we can properly tracksentanddroppedmetrics.