1 files changed, 29 insertions, 3 deletions
diff --git a/absl/synchronization/mutex.h b/absl/synchronization/mutex.h
index ce97707f..d6890099 100644
--- a/absl/synchronization/mutex.h
+++ b/absl/synchronization/mutex.h
@@ -4,7 +4,7 @@
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//      http://www.apache.org/licenses/LICENSE-2.0
+//      https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ -61,6 +61,7 @@
 #include <cstdint>
 #include <string>
 
+#include "absl/base/const_init.h"
 #include "absl/base/internal/identity.h"
 #include "absl/base/internal/low_level_alloc.h"
 #include "absl/base/internal/thread_identity.h"
@@ -81,7 +82,7 @@
 #endif
 
 namespace absl {
-inline namespace lts_2018_12_18 {
+inline namespace lts_2019_08_08 {
 
 class Condition;
 struct SynchWaitParams;
@@ -137,7 +138,27 @@ struct SynchWaitParams;
 
 class LOCKABLE Mutex {
  public:
+  // Creates a `Mutex` that is not held by anyone. This constructor is
+  // typically used for Mutexes allocated on the heap or the stack.
+  //
+  // To create `Mutex` instances with static storage duration
+  // (e.g. a namespace-scoped or global variable), see
+  // `Mutex::Mutex(absl::kConstInit)` below instead.
   Mutex();
+
+  // Creates a mutex with static storage duration.  A global variable
+  // constructed this way avoids the lifetime issues that can occur on program
+  // startup and shutdown.  (See absl/base/const_init.h.)
+  //
+  // For Mutexes allocated on the heap and stack, instead use the default
+  // constructor, which can interact more fully with the thread sanitizer.
+  //
+  // Example usage:
+  //   namespace foo {
+  //   ABSL_CONST_INIT Mutex mu(absl::kConstInit);
+  //   }
+  explicit constexpr Mutex(absl::ConstInitType);
+
   ~Mutex();
 
   // Mutex::Lock()
@@ -880,11 +901,15 @@ class SCOPED_LOCKABLE ReleasableMutexLock {
 };
 
 #ifdef ABSL_INTERNAL_USE_NONPROD_MUTEX
+inline constexpr Mutex::Mutex(absl::ConstInitType) : impl_(absl::kConstInit) {}
+
 #else
 inline Mutex::Mutex() : mu_(0) {
   ABSL_TSAN_MUTEX_CREATE(this, __tsan_mutex_not_static);
 }
 
+inline constexpr Mutex::Mutex(absl::ConstInitType) : mu_(0) {}
+
 inline CondVar::CondVar() : cv_(0) {}
 #endif
 
@@ -1015,7 +1040,7 @@ enum class OnDeadlockCycle {
 // the manner chosen here.
 void SetMutexDeadlockDetectionMode(OnDeadlockCycle mode);
 
-}  // inline namespace lts_2018_12_18
+}  // inline namespace lts_2019_08_08
 }  // namespace absl
 
 // In some build configurations we pass --detect-odr-violations to the
@@ -1027,4 +1052,5 @@ void SetMutexDeadlockDetectionMode(OnDeadlockCycle mode);
 extern "C" {
 void AbslInternalMutexYield();
 }  // extern "C"
+
 #endif  // ABSL_SYNCHRONIZATION_MUTEX_H_