[ThinLTO] Asynchronous caching #8614
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All existing kinds of `ModuleCacheEntry` contain the same kind of optionality: their `getEntryPath()`, `tryLoadingBuffer()` and `write()` functions are no-op if the ThinLTO key could not be computed in their constructors. This patch extracts the concept of no-op cache entry into `NullModuleCacheEntry`, simplifying the logic. (cherry picked from commit b168a63)
[ThinLTO] Asynchronous caching (cherry picked from commit 03af59c)
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@swift-ci please test |
akyrtzi
approved these changes
Apr 19, 2024
nkcsgexi
approved these changes
Apr 20, 2024
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@swift-ci please test windows platform |
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@swift-ci please test |
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@swift-ci please test windows platform |
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@swift-ci please test windows platform |
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Cherry-pick of #8236.
Explanation: ThinLTO performs cache operations synchronously on a thread pool. If they happen to be slow (e.g. using a remote cache with poor latency/throughput), the requests can block threads for a long period of time and slow down the build. This patch makes cache requests asynchronous and starts performing codegen locally, avoiding unnecessary waits on slow cache.
Risk: Moderate. The changes are non-trivial and the asynchronous nature makes it hard to programatically test.
Testing: Existing tests exercise the affected code path, manual testing with fault injection was performed but not easy to replicate in automated tests.
Reviewed By: @akyrtzi