Previously, on Windows Vista and later, we'd use the Windows native
SRWLock APIs. However they turned out to be semantically incompatible
with pthread read-write locks and/or plain buggy. This patch makes sure
that the custom implementation that was previously only used on old
Windows versions is now used everywhere.
This patch fixes a number of issues with the old fallback
implementation. Specifically:
* The reader count would not be incremented when a thread successfully
acquired a read lock while another thread *also* held a read lock.
* `uv_rwlock_tryrdlock()` and `uv_rwlock_trywrlock()` now
consistently return UV_EBUSY when a lock couldn't be acquired.
* Any unexpected errors now cause libuv to abort, with the exception of
`uv_rwlock_init()`.
See also https://github.com/libuv/libuv/issues/515.
PR-URL: https://github.com/libuv/libuv/pull/525
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>
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