Summary:
This test regularly times out under load.

I made a benchmark diff (prior to this in the stack, but not to be landed) which confirms (a) that the slowness of this test is due to spawning excessively-many threads, and (b) that the performance of ConcurrentSkipList doesn't unduly degrade with excessively-many threads. Conclusion: it is safe to simplify these tests.

To simplify the test, I ratcheted down the number of threads, but also bumped the number of iterations. Much more work is being done (so this test should retain its race-condition-hunting properties), but the time spent is much less, even when the system is under load.

Reviewed By: yfeldblum

Differential Revision: D33269899

fbshipit-source-id: 9f7a0ec5f3c1077c91e5d09c89f3752d552a6320