Fix mutex lock issue at the end of tsan test

Summary:
During tsan test, sometimes annotationGuard() is called after kAnnotationMutexes is already destroyed which throws exception.
This change fix the issue by uses Indestructible for kAnnotationMutexes, so that it is not destroyed.

Reviewed By: yfeldblum

Differential Revision: D25443571

fbshipit-source-id: 69411a7edc4f96ba8c7d08bd29f87ab7b2ff78ae

folly/SharedMutex.cpp

@@ -15,6 +15,7 @@
  */
 
 #include <folly/SharedMutex.h>
+#include <folly/Indestructible.h>
 
 namespace folly {
 // Explicitly instantiate SharedMutex here:
@@ -28,9 +29,10 @@ std::unique_lock<std::mutex> annotationGuard(void* ptr) {
     // the address. If the array is of prime size things will work out okay
     // without a complicated hash function.
     static constexpr std::size_t kNumAnnotationMutexes = 251;
-    static std::array<std::mutex, kNumAnnotationMutexes> kAnnotationMutexes{};
+    static Indestructible<std::array<std::mutex, kNumAnnotationMutexes>>
+        kAnnotationMutexes;
     auto index = reinterpret_cast<uintptr_t>(ptr) % kNumAnnotationMutexes;
-    return std::unique_lock<std::mutex>(kAnnotationMutexes[index]);
+    return std::unique_lock<std::mutex>((*kAnnotationMutexes)[index]);
   } else {
     return std::unique_lock<std::mutex>();
   }