Fix a logmon goroutine and memory leak #11261
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added 3 commits
October 5, 2021 12:10
Mostly to use testify assertions and close open resources
Fix a logmon leak causing high goroutine and memory usage when a task restarts. Logmon `FileRotator` buffers the task stdout/stderr streams and periodically flushing them to log files. Logmon creates a new FileRotator for each stream for each task run. However, the `flushPeriodically` goroutine is leaked when a task restarts, holding a reference to a no-longer-needed `FileRotator` instance along with its 64kb buffer. The cause is that the code assumed `time.Ticker.Stop()` closes the ticker channel, thereby terminating the goroutine, but the documentation says otherwise: > Stop turns off a ticker. After Stop, no more ticks will be sent. Stop does not close the channel, to prevent a concurrent goroutine reading from the channel from seeing an erroneous "tick". https://pkg.go.dev/time#Ticker.Stop
schmichael
approved these changes
Oct 5, 2021
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Fix a logmon leak causing high goroutine and memory usage when a task
restarts.
Logmon
FileRotatorbuffers the task stdout/stderr streams andperiodically flushing them to log files. Logmon creates a new
FileRotator for each stream for each task run. However, the
flushPeriodicallygoroutine is leaked when a task restarts,holding a reference to a no-longer-needed
FileRotatorinstancealong with its 64kb buffer.
The cause is that the code assumed
time.Ticker.Stop()closes theticker channel, thereby terminating the goroutine, but the documentation
says otherwise:
The PR adds https://github.com/uber-go/goleak dependency for detecting leaked goroutines. You can see the failures in CI about leaked goroutines in https://app.circleci.com/pipelines/github/hashicorp/nomad/17716/workflows/8fde2a15-09ae-4e21-b9a5-8e5de326f3f4/jobs/175847 but succeed with the fix commit in https://app.circleci.com/pipelines/github/hashicorp/nomad/17717/workflows/58804f90-428e-4c99-91f9-8d857b6fb979/jobs/175864.
Note, that I refactored the tests as well to use testify and ensure that file and rotator resources are closed properly for each test.
Fixes #9858