Issue 2142 - Synchronize access to s_threadInstances in CPluginClass::OnTabChanged

src/plugin/PluginClass.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2015 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 591 matching lines @@
  */
 STDMETHODIMP CPluginClass::OnTabChanged(DISPPARAMS* pDispParams, WORD wFlags)
 {
   DEBUG_GENERAL("Tab changed");
   bool newtabshown = pDispParams->rgvarg[1].intVal==3;
   if (newtabshown)
   {
     std::map<DWORD,CPluginClass*>::const_iterator it = s_threadInstances.find(GetCurrentThreadId());
     if (it == s_threadInstances.end())
     {
+      s_criticalSectionLocal.Lock();

[Eric, 2015/03/16 12:19:44]

The atomic action required here needs to surround both the call to 'find' as
well as adding a new element to the map.

Putting initialization inside the synchronized section isn't a good thing. Use
of the "test and set" pattern enables it to be outside.

       s_threadInstances[::GetCurrentThreadId()] = this;
+      s_criticalSectionLocal.Unlock();
       if (!m_isInitializedOk)
       {
         m_isInitializedOk = true;
         InitObject(true);
         UpdateStatusBar();
       }
     }
   }
   notificationMessage.Hide();
   DEBUG_GENERAL("Tab change end");
@@ skipping 1263 matching lines @@
         }
       }
     }
 
     hTabWnd = ::GetWindow(hTabWnd, GW_HWNDNEXT);
   }
 
   return hTabWnd;
 
 }