Protect state dir against concurrent operations - #245
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A big part of `zkg`'s work involves mutating its state dir, e.g., to update sources, refresh indices, or create temporary files. The code was built under the assumption that only a single `zkg` process would work on that state, so access was not controlled at all. This means that concurrent mutating operations against the state (of which we have many) could corrupt each other's expected state. Additionally, the functions we use to provide that functionality also do not cleanly cut along which part of the state they work on end to end making granular locking hard. What this patch does instead is to protect access to the manager's global state through a lock. With that all `zkg` invocations are effectively sequenced and races are impossible. This makes concurrent `zkg` invocations potentially much slower, but `zkg` was never designed for that use case anyway. We add a small test exercising concurrent, mutating access via `zkg list` which would have failed today without the lock, but it is not really clear that that operation would always perform state mutation. This closes #139 and maybe also #160 which could have had same underlying issue.
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A big part of
zkg's work involves mutating its state dir, e.g., to update sources, refresh indices, or create temporary files. The code was built under the assumption that only a singlezkgprocess would work on that state, so access was not controlled at all. This means that concurrent mutating operations against the state (of which we have many) could corrupt each other's expected state. Additionally, the functions we use to provide that functionality also do not cleanly cut along which part of the state they work on end to end making granular locking hard.What this patch does instead is to protect access to the manager's global state through a lock. With that all
zkginvocations are effectively sequenced and races are impossible. This makes concurrentzkginvocations potentially much slower, butzkgwas never designed for that use case anyway.We add a small test exercising concurrent, mutating access via
zkg listwhich would have failed today without the lock, but it is not really clear that that operation would always perform state mutation.This closes both #139 and maybe also #160 which could have had same underlying issue.