Default template parameter for SaturatingSemaphore<>

Summary:
Blocking should be the default behavior, the spinning behavior is only for niche cases and it should not be encouraged. `Baton<>` already does this.

No functional changes, only remove the argument when redundant.

Reviewed By: Gownta

Differential Revision: D49233637

fbshipit-source-id: c69a3bba2cccee9c114db0b2e1243ee122e278f5

folly/executors/test/GlobalExecutorTest.cpp

@@ -138,7 +138,7 @@ TEST(GlobalExecutorTest, GetGlobalCPUExecutorCounters) {
   const size_t numThreads = getGlobalCPUExecutorCounters().numThreads;
   const size_t numTasks = 1000 + numThreads;
   // Makes all tasks block until we're done.
-  folly::SaturatingSemaphore</* MayBlock */ true> block;
+  folly::SaturatingSemaphore<> block;
   // Ensures that the semaphore is alive until all tasks have run.
   folly::VirtualExecutor ex(getGlobalCPUExecutor());
   for (size_t i = 0; i < numTasks; ++i) {

folly/futures/HeapTimekeeper.h

@@ -44,7 +44,7 @@ class HeapTimekeeper : public Timekeeper {
 
  private:
   using Clock = std::chrono::steady_clock;
-  using Semaphore = SaturatingSemaphore</* MayBlock */ true>;
+  using Semaphore = SaturatingSemaphore<>;
 
   static constexpr size_t kQueueBatchSize = 256;
   // Queue capacity is kept in this band to make sure that it is reallocated

folly/synchronization/Latch.h

@@ -154,7 +154,7 @@ class Latch {
   }
 
   std::atomic<int32_t> count_;
-  SaturatingSemaphore</* MayBlock = */ true> semaphore_;
+  SaturatingSemaphore<> semaphore_;
 };
 
 } // namespace folly

folly/synchronization/SaturatingSemaphore.h

@@ -98,7 +98,7 @@ namespace folly {
 ///
 /// Usage:
 /// @code
-/// SaturatingSemaphore</* MayBlock = */ true> f;
+/// SaturatingSemaphore<> f;
 /// ASSERT_FALSE(f.try_wait());
 /// ASSERT_FALSE(f.try_wait_until(
 ///     std::chrono::steady_clock::now() + std::chrono::microseconds(1)));
@@ -117,7 +117,7 @@ namespace folly {
 /// ASSERT_FALSE(f.try_wait());
 /// @endcode
 
-template <bool MayBlock, template <typename> class Atom = std::atomic>
+template <bool MayBlock = true, template <typename> class Atom = std::atomic>
 class SaturatingSemaphore {
   detail::Futex<Atom> state_;
 

folly/synchronization/ThrottledLifoSem.h

@@ -156,7 +156,7 @@ class ThrottledLifoSem {
   friend class ThrottledLifoSemTestHelper;
 
   struct Waiter {
-    SaturatingSemaphore</* MayBlock */ true> wakeup;
+    SaturatingSemaphore<> wakeup;
     SafeIntrusiveListHook hook;
   };
 

folly/synchronization/test/ThrottledLifoSemTest.cpp

@@ -161,7 +161,7 @@ TEST(ThrottledLifoSem, MPMCStress) {
 
   std::vector<std::thread> producers;
   std::vector<std::thread> consumers;
-  folly::SaturatingSemaphore</* MayBlock */ true> done;
+  folly::SaturatingSemaphore<> done;
   std::atomic<size_t> handoffs = 0;
   for (size_t t = 0; t < kNumThreads; ++t) {
     producers.emplace_back([&] {