[chenBright]

What problem does this PR solve?

Issue Number: resolve

Problem Summary:

bthread_sem_post() and bthread_sem_post_n() used relaxed ordering when adding permits.
This did not publish preceding writes to consumers that successfully acquired permits without
blocking in butex_wait(), potentially causing data races on shared payloads.

What is changed and the side effects?

Changed:

Use memory_order_release in the shared post implementation, pairing with successful acquire
CAS operations in wait, timedwait, and trywait.

Side effects:

• Performance effects:

• Breaking backward compatibility:

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Check List:

• Please make sure your changes are compilable.
• When providing us with a new feature, it is best to add related tests.
• Please follow Contributor Covenant Code of Conduct.

[Copilot]

🟡 Changes recommended

The only remaining active finding is a nit in src/bthread/semaphore.cpp:117, where unrelated locals in bthread_sem_post() lost their const qualifiers, so the diff goes beyond the release-ordering fix it is meant to contain.

1 open issue

• Preserve const qualifiers on unchanged locals · New

What changed in this PR

This PR fixes a memory-ordering bug in the bthread semaphore. bthread_sem_post() and bthread_sem_post_n() added permits with relaxed ordering. A waiter that gets a permit without blocking in butex_wait() could then miss writes made before the post, which can cause data races on shared data. The fix makes the permit update a release operation, which pairs with the successful acquire compare-and-swap (CAS) in wait, timedwait, and trywait.

Changes:

• Change the permit fetch_add in bthread_sem_post from relaxed to release ordering, with a comment explaining why.
• Add stress tests that check payload visibility for bthread_sem_post and bthread_sem_post_n across the wait, timed wait, and try-wait paths.

File	Description
test/​bthread_semaphore_unittest.cpp	Adds helper threads and tests that check payload visibility after a successful permit acquire for post and post_n.
src/​bthread/​semaphore.cpp	Uses release ordering for the permit update in bthread_sem_post, which publishes earlier writes to waiters that acquire without blocking.

_{Review effort: Lite}

[wasphin]

LGTM