fix(kernel): package cache fails under parallelism #4215
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The package cache mechanism that was turned on by default in #4181 works in theory under parallelism, but not in practice. Typically the CDK CLI will prevent CDK apps from running in parallel, but Python testing frameworks like `tox` use subprocess parallelism to speed up test runs, leading to the jsii imports being executed at the same time. Since jsii is sync, the locking needs to be sync. The sync locking feature of the `lockfile` library doesn't have wait support (for good reason), and so when a lock is already acquired by another process it quickly burns through its 12 retries in a hot loop, and then exits with an error. Two changes to address this: - (Ab)use `Atomics.wait()` to get a synchronous sleeping primitive; since `lockSync` doesn't support synchronous sleep, we build our own retry loop with synchronous sleep around `lockSync`. - Since the extracted directory is immutable: if the marker file in the extracted directory exists, we can treat it as evidence that the directory has been completely written and we can skip trying to vy for exclusive access to write it. This avoids all lock contention after the very first CDK app execution. Fixes #4207.
kaizencc
approved these changes
Aug 9, 2023
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Thank you for contributing! ❤️ I will now look into making sure the PR is up-to-date, then proceed to try and merge it! |
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Merging (with squash)... |
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The package cache mechanism that was turned on by default in #4181 works in theory under parallelism, but not in practice.
Typically the CDK CLI will prevent CDK apps from running in parallel, but Python testing frameworks like
toxuse subprocess parallelism to speed up test runs, leading to the jsii imports being executed at the same time.Since jsii is sync, the locking needs to be sync. The sync locking feature of the
lockfilelibrary doesn't have wait support (for good reason), and so when a lock is already acquired by another process it quickly burns through its 12 retries in a hot loop, and then exits with an error.Two changes to address this:
Atomics.wait()to get a synchronous sleeping primitive; sincelockSyncdoesn't support synchronous sleep, we build our own retry loop with synchronous sleep aroundlockSync.Fixes #4207.
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.