Before this patch an uv_mutex_t (backed by a critical section) could be
released by a tread different from the thread that acquired it, which is
not allowed. This is fixed by using a semaphore instead.
Note that the affected code paths were used on Windows XP and Windows
Server 2003 only.
Fixes: https://github.com/libuv/libuv/issues/515
PR-URL: https://github.com/libuv/libuv/pull/516
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>
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