Summary: `std::unique_lock` constructor allows to create a unique lock without locking the mutex. `std::unique_lock::try_lock` returns true if mutex has been acquired successfully, and false otherwise. It could be that an exception is being thrown while trying to acquire mutex, which is not modeled.
Reviewed By: jberdine
Differential Revision: D6185568
fbshipit-source-id: 192bf10
Daiva Naudziuniene