fix thread safe bug

test=develop

paddle/fluid/platform/device_context.cc

@@ -92,26 +92,24 @@ platform::TemporaryAllocator& DeviceTemporaryAllocator::Get(
     const platform::Place& place, const cudaStream_t& stream) {
   PADDLE_ENFORCE(platform::is_gpu_place(place));
   auto place_stream = std::make_pair(place, stream);
-  {
   std::unique_lock<std::mutex> lock(mtx_);
-    if (!device_allocator_.count(place_stream)) {
-      device_allocator_[place_stream].reset(new TemporaryAllocator(place));
-      device_allocator_[place_stream]->SetCallback([stream]() {
+  auto it = device_allocator_.find(place_stream);
+  if (it == device_allocator_.end()) {
+    auto tmp_allocator = new TemporaryAllocator(place);
+    tmp_allocator->SetCallback([stream]() {
       PADDLE_ENFORCE(cudaStreamSynchronize(stream));
       PADDLE_ENFORCE(cudaGetLastError());
     });
+    device_allocator_[place_stream].reset(tmp_allocator);
+    return *tmp_allocator;
+  } else {
+    return *it->second;
   }
-  }
-  return *device_allocator_.at(place_stream);
 }
 
 template <>
 platform::TemporaryAllocator& DeviceTemporaryAllocator::Get(
     const platform::CUDADeviceContext& dev_ctx) {
-  auto place_stream = std::make_pair(dev_ctx.GetPlace(), dev_ctx.stream());
-  if (device_allocator_.count(place_stream)) {
-    return *device_allocator_.at(place_stream);
-  }
   return Get(dev_ctx.GetPlace(), dev_ctx.stream());
 }
 #endif
@@ -325,7 +323,7 @@ Place CUDADeviceContext::GetPlace() const { return place_; }
 void CUDADeviceContext::Wait() const {
   auto& allocator =
       DeviceTemporaryAllocator::Instance().Get<CUDADeviceContext>(*this);
-  allocator.Release([=]() {
+  allocator.Release([this]() {
     PADDLE_ENFORCE(cudaStreamSynchronize(stream_));
     PADDLE_ENFORCE(cudaGetLastError());
   });