[WASM_WORKERS] Fix UB in pthread_mutex with debug+hybrid builds in pthread_mutex_unlock.c - #1
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Jul 10, 2026
…ore#27284) $doReadv reads iovec-by-iovec via `FS.read`. On a non-blocking socket, `FS.read` (nodeSockOps.recvmsg) throws EAGAIN when the queue is empty, unlike a regular file which returns 0. If an earlier iovec already consumed data and filled exactly to its length (so the `if (curr < len) break` doesn't fire), the loop advances to the next iovec, whose `FS.read` throws EAGAIN. The exception escaped `doReadv`, discarding the accumulated `ret`, so the whole `readv(2)` failed with EAGAIN even though bytes were read. POSIX readv/writev are single gather operations: they return the available byte count and never fail after partial success. Observed with an mio `TcpStream` (NODERAWSOCKETS + PROXY_TO_PTHREAD + JSPI) where an echo returned as two TCP chunks: `read_vectored` with two iovecs hit recvmsg on iovec #1 (12 bytes, drains recvq) then recvmsg EMPTY on iovec #2 (next chunk not yet arrived), throwing WouldBlock for the whole call. A single-buffer read never hits it — matching "read works, readv fails". It is timing-sensitive: if both chunks are queued before the read, iovec #2 succeeds. - `doReadv` and `doWritev` now catch `EAGAIN`/`EWOULDBLOCK` `FS.ErrnoError` from a subsequent iovec and return the accumulated count when `ret > 0`, only rethrowing when `ret == 0` (nothing transferred yet, so the would-block belongs to the first iovec). Adds `test/fs/test_readv_eagain.c` (wired up as `test_fs_readv_eagain`), which registers custom devices that satisfy the first iovec fully then throw EAGAIN, asserting both `readv` and `writev` return the partial count rather than failing. The test aborts without the fix and passes with it.
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Followup of emscripten-core#26673