[DesktopCapturer] FallbackDesktopCapturerWrapper and its tests

webrtc/modules/desktop_capture/shared_memory.cc

 /*
  *  Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #include "webrtc/modules/desktop_capture/shared_memory.h"
 
+#include <utility>
+
+#include "webrtc/base/checks.h"
+
 namespace webrtc {
 
 #if defined(WEBRTC_WIN)
 const SharedMemory::Handle SharedMemory::kInvalidHandle = NULL;
 #else
 const SharedMemory::Handle SharedMemory::kInvalidHandle = -1;
 #endif
 
 SharedMemory::SharedMemory(void* data, size_t size, Handle handle, int id)
   : data_(data),
     size_(size),
     handle_(handle),
     id_(id) {
 }
 
+SharedMemoryFactoryWrapper::SharedMemoryFactoryWrapper(
+    std::unique_ptr<SharedMemoryFactory> factory) {
+  RTC_DCHECK(factory);
+  owned_factory_ = std::move(factory);
+  shared_factory_ = owned_factory_.get();
+}
+
+SharedMemoryFactoryWrapper::SharedMemoryFactoryWrapper(
+    SharedMemoryFactory* factory) {
+  RTC_DCHECK(factory);
+  shared_factory_ = factory;
+}
+
+SharedMemoryFactoryWrapper::~SharedMemoryFactoryWrapper() = default;
+
+std::unique_ptr<SharedMemoryFactory> SharedMemoryFactoryWrapper::Wrap() const {
+  return std::unique_ptr<SharedMemoryFactory>(new SharedMemoryFactoryWrapper(

[Sergey Ulanov, 2017/02/15 23:08:43]

A better solution would be use a ref-counted holder for SharedMemoryFactory, so
the shared factory is destroyed only after all "wrappers" are destroyed.
SharedDesktopFrame works this way. There is nothing in DesktopCapturer interface
to guarantee that capturers stop using this factory when they are destroyed.
DesktopCapturer implementations are allowed to capture on a separate thread (see
DesktopCaptureProxy). Again this may not be a problem right now, but it should
be documented somewhere.

[Hzj_jie, 2017/02/16 01:57:07]

I have added comments for both SharedMemoryFactoryWrapper class and
CreateSharedMemory() function.
Considering this class is becoming complex, I added test cases.

+      owned_factory_.get()));
+}
+
+std::unique_ptr<SharedMemory> SharedMemoryFactoryWrapper::CreateSharedMemory(
+    size_t size) {
+  return shared_factory_->CreateSharedMemory(size);
+}
+
 }  // namespace webrtc