Explicitly name hazptr thread pool (#1512)

Summary:
Pull Request resolved: https://github.com/facebook/folly/pull/1512

Hazptr library creates its own CPU executor which name interfere with default executor name. We want to avoid this.
Also insure that the thread is permanent, otherwise folly runtime may destroy and recreate it periodically.

Reviewed By: magedm

Differential Revision: D25708252

fbshipit-source-id: 2b41ad4fa28d2ba9c9bd69bc5d4a02b933d79e66

folly/synchronization/HazptrThreadPoolExecutor.cpp

@@ -23,7 +23,9 @@ namespace {
 
 struct HazptrTPETag {};
 folly::Singleton<folly::CPUThreadPoolExecutor, HazptrTPETag> hazptr_tpe_([] {
-  return new folly::CPUThreadPoolExecutor(1);
+  return new folly::CPUThreadPoolExecutor(
+      std::make_pair(1, 1),
+      std::make_shared<folly::NamedThreadFactory>("hazptr-tpe-"));
 });
 
 folly::Executor* get_hazptr_tpe() {