There was a memory corruption issue with the pthread barrier
implementation on android, where a barrier could still be in use by one
thread when being freed by another.
This fixes that issue and adds lots of missing error handling.
This implementation is now also used for the OSX fallback.
Fixes: https://github.com/libuv/libuv/issues/615
PR-URL: https://github.com/libuv/libuv/pull/790
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
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