Check for max value in test semaphore

Summary: [Folly] Check for max value in test semaphore, beyond which posts cannot be tolerated.

Reviewed By: aary

Differential Revision: D15938166

fbshipit-source-id: 1f3fee97a9662dafc5b434c0449831147aa3c976

folly/synchronization/test/Semaphore.h

@@ -77,6 +77,9 @@ class Semaphore {
   template <typename PrePost>
   void post(PrePost pre_post) {
     std::unique_lock<std::mutex> l{m_};
+    if (value_ == -size_t(1)) {
+      throw_exception<std::logic_error>("overflow");
+    }
     pre_post();
     if (!waiting_) {
       ++value_;