Use LINKER_INITIALIZED for mutexes with static storage class.

This was causing exit-time races as some threads were accessing the
mutex as it was being destructed.

			---------------

It is illegal to use any static type with a constructor/destructor with static
storage class in a multithreaded C++ programme that can exit(), even if the
constructor is protected by C++11's function-scope static initialization rules,
because exit-time destruction is unsafe in the presence of multiple threads.

For things that are not function-scope, the construction is also unsafe,
because global contruction ordering is undefined in general.

The LINKER_INITIALIZED variant constructor for TensorFlow's mutex avoids these
problems, at the cost of relying on the linker to zero-initialize the BSS
region.

PiperOrigin-RevId: 176612772

1 files changed, 1 insertions, 1 deletions

diff --git a/tensorflow/contrib/nccl/kernels/nccl_manager.cc b/tensorflow/contrib/nccl/kernels/nccl_manager.cc
index 1eb1481675..31a35b0d53 100644
--- a/tensorflow/contrib/nccl/kernels/nccl_manager.cc
+++ b/tensorflow/contrib/nccl/kernels/nccl_manager.cc
@@ -370,7 +370,7 @@ void NcclManager::AddParticipant(int num_devices, const string& key,
 }
 
 void NcclManager::RunCollective(const string& key, Collective* collective) {
-  static mutex collective_mu;
+  static mutex collective_mu(LINKER_INITIALIZED);
 
   auto* communicator = GetCommunicator(collective);
   collective->communicator = communicator;