Fix deadlock caused by syncing during destroy #2852
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When replacing an alloc the new alloc is blocked until the old alloc is destroyed. This could cause a deadlock: 1. Destroying the old alloc includes a final sync of its status 2. Syncing status causes a GC 3. A GC looks for terminal allocs to cleanup 4. The GC waits for an alloc to stop completely before GC'ing If the GC chooses the currently-being-destroyed-alloc to GC, the GC deadlocks. If `client.max_parallel` deadlocks happen the GC is wedged until the Nomad process is restarted. Performing the final sync asynchronously is an ugly hack but prevents the deadlock by allowing the final sync to occur after the alloc runner has shutdown and been destroyed.
dadgar
approved these changes
Jul 18, 2017
This was referenced Jul 19, 2017
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When replacing an alloc the new alloc is blocked until the old alloc is
destroyed. This could cause a deadlock:
If the GC chooses the currently-being-destroyed-alloc to GC, the GC
deadlocks. If
client.max_paralleldeadlocks happen the GC is wedgeduntil the Nomad process is restarted.
Performing the final sync asynchronously is an ugly hack but prevents
the deadlock by allowing the final sync to occur after the alloc runner
has shutdown and been destroyed.