405a8f53d3
In LuceneChangeIndex, we schedule the future by calling (essentially) MoreExecutors.listeningDecorator(threadPool).submit() this returns a TrustedListenableFutureTask, a Future implemented by Guava, and we wait on this one. The implementation passes this off to ScheduledThreadPoolExecutor for running. This interprets it as a Runnable in AbstractExecutorService#submit(), and a Runnable has no call surface for cancellation. This means that the guava future is never canceled if the corresponding ScheduledFutureTask is canceled. Server#stop shuts down all thread pools. Since the pools are created with setExecuteExistingDelayedTasksAfterShutdownPolicy(false) all pending work is canceled. The problem would trigger in the following circumstances: * For tests that schedule two or more ref updates at the end of the test. Since the interactive pool has size 1, that could delay a piece of work to be delayed. * Executors are shutdown in creation order, which is random. It would only trigger if the interactive pool was shutdown before the batch pool. The problem could be reliably reproduced by building with Bazel, setting shard_count=30 on //gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/rest/project:rest_project, and running shard 10 (which exhibited the problem) 50-way parallel on a 12 HT-core system. Things to note: * If we have to use ListenableFutures, then it would be nice if we could use a Executor that actually works together well with Guava. * Server#stop discards pending work. In particular, work scheduled by ReindexAfterUpdate can be discarded, potentially leaving the index inconsistent. * ReindexAfterUpdate runs in the batch executor, but then schedules its search work on the interactive executor, which is gratuitously parallel. * WorkQueue.Executor is a lot of cognitive overhead for providing a list of processes. Can't administrators just run jstack? * A randomized creation order for threadpools causes randomized shutdown order, making problems harder to reproduce. Bug: Issue 4466 Change-Id: I55c3b85c66433de7ee9e037fc243abe705080bbc |
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