repro: add tests reproducing Session data races under free-threading#3727
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repro: add tests reproducing Session data races under free-threading#3727crowecawcaw wants to merge 1 commit into
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A single botocore.session.Session lazily builds and caches shared state (components, credentials, parsed config) and HierarchicalEmitter mutates a shared handler trie, using check-then-act without synchronization. These races are latent under the GIL (the ~5ms switch interval makes the window rare) but reproduce when a Session is shared across threads on a free-threaded (no-GIL) build, where threads run Python in parallel. These tests reproduce four such races and are written to fail on the current code: - ComponentLocator.get_component builds a deferred component more than once under concurrent first-access. - Session.get_credentials loads credentials more than once. - Session.full_config parses the config files more than once. - HierarchicalEmitter concurrent registration loses handlers via a check-then-act node creation in _PrefixTrie.append_item. They use delay-injection (a sleep in the lazy-init window, so the factory should still run exactly once) and identity invariants (all threads should observe the same singleton), and shrink the thread-switch interval to widen the window on the GIL build. Each fails deterministically on both the default and free-threaded builds, and passes once the shared state is synchronized. Tests generated with AI assistance and reviewed by me.
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A single botocore.session.Session lazily builds and caches shared state (components, credentials, parsed config) and HierarchicalEmitter mutates a shared handler trie, using check-then-act without synchronization. These races are latent under the GIL (the ~5ms switch interval makes the window rare) but reproduce when a Session is shared across threads on a free-threaded (no-GIL) build, where threads run Python in parallel.
These tests reproduce four such races and are written to fail on the current code.
They use delay-injection (a sleep in the lazy-init window, so the factory should still run exactly once) and identity invariants (all threads should observe the same singleton), and shrink the thread-switch interval to widen the window on the GIL build.
Tests generated with AI assistance and reviewed by me. Not exactly intended to be merged as is, but more to demonstrate the issue.
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