Fix deadlock between UI thread and drag and drop thread on Windows.

ui/base/dragdrop/os_exchange_data_provider_win.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/base/dragdrop/os_exchange_data_provider_win.h"
 
 #include <algorithm>
 #include <vector>
 
 #include "base/files/file_path.h"
@@ skipping 472 matching lines @@
 }
 
 bool OSExchangeDataProviderWin::HasCustomFormat(CLIPFORMAT format) const {
   FORMATETC format_etc =
       { format, NULL, DVASPECT_CONTENT, -1, TYMED_HGLOBAL };
   return (source_object_->QueryGetData(&format_etc) == S_OK);
 }
 
 void OSExchangeDataProviderWin::SetDownloadFileInfo(
     const OSExchangeData::DownloadFileInfo& download) {
-  // If the filename is not provided, set stoarge to NULL to indicate that
+  // If the filename is not provided, set storage to NULL to indicate that
   // the delay rendering will be used.
+  // TODO(dcheng): Is it actually possible for filename to be empty here? I
+  // think we always synthesize one in WebContentsDragWin.
   STGMEDIUM* storage = NULL;
   if (!download.filename.empty())
     storage = GetStorageForFileName(download.filename);
 
   // Add CF_HDROP.
   DataObjectImpl::StoredDataInfo* info = new DataObjectImpl::StoredDataInfo(
       ClipboardUtil::GetCFHDropFormat()->cfFormat, storage);
   info->downloader = download.downloader;
   data_->contents_.push_back(info);
 }
 
+void OSExchangeDataProviderWin::SetInDragLoop(bool in_drag_loop) {
+  data_->set_in_drag_loop(in_drag_loop);
+}
+
 #if defined(USE_AURA)
 
 void OSExchangeDataProviderWin::SetDragImage(
     const gfx::ImageSkia& image,
     const gfx::Vector2d& cursor_offset) {
   drag_image_ = image;
   drag_image_offset_ = cursor_offset;
 }
 
 const gfx::ImageSkia& OSExchangeDataProviderWin::GetDragImage() const {
@@ skipping 74 matching lines @@
       break;
   }
 
   destination->tymed = source->tymed;
   destination->pUnkForRelease = source->pUnkForRelease;
   if (destination->pUnkForRelease)
     destination->pUnkForRelease->AddRef();
 }
 
 DataObjectImpl::DataObjectImpl()
     : is_aborting_(false),

[jianli, 2013/04/26 01:07:18]

in_drag_loop_ is not initialized.

[dcheng, 2013/04/26 18:05:44]

Done.

       in_async_mode_(false),
       async_operation_started_(false),
       observer_(NULL) {
 }
 
 DataObjectImpl::~DataObjectImpl() {
   StopDownloads();
   STLDeleteContainerPointers(contents_.begin(), contents_.end());
   if (observer_)
     observer_->OnDataObjectDisposed();
@@ skipping 56 matching lines @@
 
   StoredData::iterator iter = contents_.begin();
   while (iter != contents_.end()) {
     if ((*iter)->format_etc.cfFormat == format_etc->cfFormat &&
         (*iter)->format_etc.lindex == format_etc->lindex &&
         ((*iter)->format_etc.tymed & format_etc->tymed)) {
       // If medium is NULL, delay-rendering will be used.
       if ((*iter)->medium) {
         DuplicateMedium((*iter)->format_etc.cfFormat, (*iter)->medium, medium);
       } else {
-        // Check if the left button is down.
-        bool is_left_button_down = (GetKeyState(VK_LBUTTON) & 0x8000) != 0;
+        // Fail all GetData() attempts for DownloadURL data if the drag and drop
+        // operation is still in progress.
+        if (in_drag_loop_)
+          return DV_E_FORMATETC;
 
         bool wait_for_data = false;
-        if ((*iter)->in_delay_rendering) {
-          // Make sure the left button is up. Sometimes the drop target, like
-          // Shell, might be too aggresive in calling GetData when the left
-          // button is not released.
-          if (is_left_button_down)
-            return DV_E_FORMATETC;
 
-          // In async mode, we do not want to start waiting for the data before
-          // the async operation is started. This is because we want to postpone
-          // until Shell kicks off a background thread to do the work so that
-          // we do not block the UI thread.
-          if (!in_async_mode_ || async_operation_started_)
-            wait_for_data = true;
-        } else {
-          // If the left button is up and the target has not requested the data
-          // yet, it probably means that the target does not support delay-
-          // rendering. So instead, we wait for the data.
-          if (is_left_button_down) {

[jianli, 2013/04/26 01:07:18]

I am a bit concerned about this logic being removed. Could you please do more
testing on this, like on XP?

[dcheng, 2013/04/26 18:05:44]

I have tested on XP, Vista, 7, and 8, and it works on all of them.

-            (*iter)->in_delay_rendering = true;
-            memset(medium, 0, sizeof(STGMEDIUM));
-          } else {
-            wait_for_data = true;
-          }
-        }
+        // In async mode, we do not want to start waiting for the data before
+        // the async operation is started. This is because we want to postpone
+        // until Shell kicks off a background thread to do the work so that
+        // we do not block the UI thread.
+        if (!in_async_mode_ || async_operation_started_)
+          wait_for_data = true;
 
         if (!wait_for_data)
           return DV_E_FORMATETC;
 
         // Notify the observer we start waiting for the data. This gives
         // an observer a chance to end the drag and drop.
         if (observer_)
           observer_->OnWaitForData();
 
         // Now we can start the download.
@@ skipping 47 matching lines @@
     *local_medium = *medium;
   } else {
     DuplicateMedium(format_etc->cfFormat, medium, local_medium);
   }
 
   DataObjectImpl::StoredDataInfo* info =
       new DataObjectImpl::StoredDataInfo(format_etc->cfFormat, local_medium);
   info->medium->tymed = format_etc->tymed;
   info->owns_medium = !!should_release;
   // Make newly added data appear first.
+  // TODO(dcheng): Make various setters agree whether elements should be
+  // prioritized from front to back or back to front.
   contents_.insert(contents_.begin(), info);
 
   return S_OK;
 }
 
 HRESULT DataObjectImpl::EnumFormatEtc(
     DWORD direction, IEnumFORMATETC** enumerator) {
   if (direction == DATADIR_GET) {
     FormatEtcEnumerator* e =
         new FormatEtcEnumerator(contents_.begin(), contents_.end());
@@ skipping 204 matching lines @@
   return new OSExchangeDataProviderWin();
 }
 
 // static
 OSExchangeData::CustomFormat OSExchangeData::RegisterCustomFormat(
     const std::string& type) {
   return RegisterClipboardFormat(ASCIIToUTF16(type).c_str());
 }
 
 }  // namespace ui