Make EventedFileUpdateChecker garbage collectable #40133
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jonathanhefner
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kaspth
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When an `EventedFileUpdateChecker` instance detects a watched directory that previously did not exist, it calls `shutdown!` and then `boot!` to reinitialize its underlying listener. Prior to this commit, `shutdown!` invoked `Listen.stop` which stops **all** listeners, globally. This commit changes `shutdown!` to stop the checker's listener only. Fixes rails#38174.
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The Listen gem dispatches "file changed" events from a separate thread. This thread holds a reference to the `changed` callback, and runs until the listener is stopped. Thus, objects that are part of the `changed` callback's scope cannot be garbage collected until the listener is stopped. This commit isolates the `changed` callback and associated scope in an `EventedFileUpdateChecker::Core` instance. This ensures that the `EventedFileUpdateChecker` instance can be garbage collected. Additionally, this commit adds a finalizer to the `EventedFileUpdateChecker` instance, which stops the listener and ensures that the `EventedFileUpdateChecker::Core` instance can be garbage collected.
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jonathanhefner
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| wait # Wait for listener thread to start processing events. | ||
| GC.start |
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This test uncovered a race condition in Listen / rb-inotify (see guard/rb-inotify#100) that manifests here as a hang when the finalizer stops the listener. However, I don't think it's likely that a normal application would trigger the race condition, so I think this PR is safe to merge. (I've added a wait here to prevent the test itself from triggering the race condition.)
kaspth
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| end | ||
| end | ||
| def common_path(paths) | ||
| paths.map { |path| path.ascend.to_a }.reduce(&:&)&.first |
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Behold the three meditating munks! Bringing offerings of :, ) and . &:&)&. 😄
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A little bit of Ruby poetry! 😆
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The Listen gem dispatches "file changed" events from a separate thread. This thread holds a reference to the
changedcallback, and runs until the listener is stopped. Thus, objects that are part of thechangedcallback's scope cannot be garbage collected until the listener is stopped.This commit isolates the
changedcallback and associated scope in anEventedFileUpdateChecker::Coreinstance. This ensures that theEventedFileUpdateCheckerinstance can be garbage collected. Additionally, this commit adds a finalizer to theEventedFileUpdateCheckerinstance, which stops the listener and ensures that theEventedFileUpdateChecker::Coreinstance can be garbage collected.This is based on top of #40100.
I split this PR into two commits to make it easier to review. The first commit is a minimal diff to make
EventedFileUpdateCheckergarbage collectable. The second commit is cleanup that eliminatesEventedFileUpdateChecker::PathHelper, instead of fixing its indentation.