Fix task failure signal race condition#15917
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arhimondr merged 6 commits intotrinodb:masterfrom Feb 13, 2023
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core/trino-main/src/main/java/io/trino/execution/SqlTaskManager.java
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core/trino-main/src/main/java/io/trino/server/TaskResource.java
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nit: move to a separate commit
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Actually, this is all related code. The movement to here alone would cause issues with scheduleDriversWithTaskLifecycle() not being called when taskHandle == null. This is "fine" because it doesn't break the task state machine model today, but causes problems in a world with terminating task states.
core/trino-main/src/main/java/io/trino/execution/buffer/LazyOutputBuffer.java
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The assumption is that sending emptyResults(taskInstanceId, 0, completed: false) is safe, even though the previous comment suggested otherwise, because TaskResource will respond similarly when the timeout threshold is reached. Sending these responses instead of letting them time out should propagate task failure information more quickly than allowing the timeout to expire.
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Previously, SqlTaskExecution registered an outputBuffer callback for CheckTaskCompletionOnBufferFinish in the constructor, which published a reference to "this" that could become visible to another thread in an unsafe way. This callback was moved to the start() method instead. SqlTask is also reordered to call SqlTaskExecution#start() before publishing a reference to it via the TaskHolder reference, which was unsafe under concurrent state machine activity on another thread. Instead, taskHolderReference updates must now synchronize on a single taskHolderLock before mutating the holder reference.
Sends responses eagerly to pending readers in LazyOutputBuffer when a task aborts the output buffer.
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Description
Fixes the sequence of operations around
TaskResourcechecking for task failure until after the buffer response future is completed. Otherwise, tasks could inappropriately announce completion rather than failure to consumers which can yield incorrect query results.Additional context and related issues
Discovered while attempting to debug a swath of test failures producing incorrect results in #15478 which made the sequence of interleaving operations necessary to trigger the correctness bug more likely to occur.
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