Protect admissionStrategy by a SharedMutex
Protect admissionStrategy by a SharedMutex

Summary: With this protection, we'll be able to change it dynamically at runtime.

Reviewed By: spalamarchuk

Differential Revision: D13259596

fbshipit-source-id: 8f868a2ff665db7090a36f6fb60768db3f0961d0

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift