The restrictions on std::atomic make a it fragile to have a vector of them, and this failed to compile on Linux in CI.
While I'm in there, clean up a couple of tests that repeated a raw `10` for the thread count.
rdar://problem/49709062
Many of these tests would fail if one of the test threads didn't begin execution within 100 milliseconds. They would hit while (!done) the very first time and never execute the loop body. That does happen from time to time, and the result would be a spurious failure. Change the loops to do {} while(!done) to ensure they always execute at least one iteration.
Many tests also had the test threads concurrently write results to a std::vector, which appeared to be causing some failures in my local testing when I had extra sleeps inserted to simulate pathological scheduling. Change the results vectors to be vectors of std::atomic to ensure that this concurrent writing is safe.
These changes shouldn't affect its ability to test the functionality it intends to test.
rdar://problem/49386389
- added read / write lock support
- added non-fatal error support to allow use of mutex in fatal error reporting pathway
- isolated pthread implementation to it own header/cpp file pair
- expanded unit tests to cover new code as well as better test existing mutex
- removed a layer of complexity that added no real value
If the thread starts slowly enough it will succeed in taking the lock,
leading to a deadlock. We saw this test hanging on some of our bots
inside of pthread's lock acquire.
