Crash in DirectX capturer

webrtc/modules/desktop_capture/win/dxgi_output_duplicator.cc

 /*
  *  Copyright (c) 2016 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.
  */
 
@@ skipping 257 matching lines @@
   }
 
   return true;
 }
 
 void DxgiOutputDuplicator::Setup(Context* context) {
   RTC_DCHECK(context->updated_region.is_empty());
   // Always copy entire monitor during the first Duplicate() function call.
   context->updated_region.AddRect(desktop_rect_);
   for (size_t i = 0; i < contexts_.size(); i++) {
     if (contexts_[i] == nullptr) {

[Sergey Ulanov, 2016/11/11 18:27:18]

I guess this loop can be removed now.

[Hzj_jie, 2016/11/11 21:51:31]

Yes. Updated.

       contexts_[i] = context;
       return;
     }
   }
 
   contexts_.push_back(context);
 }
 
 void DxgiOutputDuplicator::Unregister(const Context* const context) {
-  for (size_t i = 0; i < contexts_.size(); i++) {
-    if (contexts_[i] == context) {
-      contexts_[i] = nullptr;
+  for (auto it = contexts_.begin(); it != contexts_.end(); it++) {

[Sergey Ulanov, 2016/11/11 18:27:18]

This loop can be replaced with std::find:
  contexts_.erase(std::find(
      contexts_.begin(), contexts_.end(), context));

[Hzj_jie, 2016/11/11 21:51:31]

Done.

+    if (*it == context) {
+      contexts_.erase(it);

[Sergey Ulanov, 2016/11/11 18:27:18]

What was the reason this code was implemented this way? I.e. why was it
necessary to replace values with nullptr instead of erasing them?

[Hzj_jie, 2016/11/11 21:51:31]

Because std::vector::erase is O(n) instead of O(1). I over-optimized this logic.

[Sergey Ulanov, 2016/11/11 22:57:35]

FWIW it can be O(1) if you swap it with the last element, we don't care about
ordering here, but IMO it's better to keep this code simpler.

[Hzj_jie, 2016/11/11 23:28:22]

Oh, yes, since we have searched already. But the newer version should only
search once.

       return;
     }
   }
 
   RTC_NOTREACHED();
 }
 
 void DxgiOutputDuplicator::SpreadContextChange(const Context* const source) {
   for (Context* dest : contexts_) {
+    RTC_DCHECK(dest);
     if (dest != source) {
       dest->updated_region.AddRegion(source->updated_region);
     }
   }
 }
 
 DesktopRect DxgiOutputDuplicator::SourceRect(DesktopRect rect) {
   // |texture_|->AsDesktopFrame() starts from (0, 0).
   rect.Translate(-desktop_rect_.left(), -desktop_rect_.top());
   return rect;
 }
 
 DesktopRect DxgiOutputDuplicator::TargetRect(DesktopRect rect,
                                              DesktopVector offset) {
   rect = SourceRect(rect);
   rect.Translate(offset);
   return rect;
 }
 
 }  // namespace webrtc