Issue #1652, #3456 - Replace 's_asyncWebBrowser2' with thread-safe facilities

src/plugin/PluginClass.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
- * Copyright (C) 2006-2015 Eyeo GmbH
+ * Copyright (C) 2006-2016 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
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
@@ skipping 10 matching lines @@
 #include "PluginMimeFilterClient.h"
 #include "AdblockPlusClient.h"
 #include "PluginClientBase.h"
 #include "PluginClientFactory.h"
 #include "PluginUtil.h"
 #include "../shared/Utils.h"
 #include "../shared/Dictionary.h"
 #include "IeVersion.h"
 #include "Instances.h"
 #include "../shared/Version.h"
+#include "Instances.h"
 #include <thread>
 #include <array>
 
 #ifdef DEBUG_HIDE_EL
 DWORD profileTime = 0;
 #endif
 
 extern CComModule _Module;
 
 typedef HANDLE (WINAPI *OPENTHEMEDATA)(HWND, LPCWSTR);
 typedef HRESULT (WINAPI *DRAWTHEMEBACKGROUND)(HANDLE, HDC, INT, INT, LPRECT, LPRECT);
 typedef HRESULT (WINAPI *CLOSETHEMEDATA)(HANDLE);
 
 HICON CPluginClass::s_hIcons[ICON_MAX] = { NULL, NULL, NULL };
 DWORD CPluginClass::s_hIconTypes[ICON_MAX] = { IDI_ICON_DISABLED, IDI_ICON_ENABLED, IDI_ICON_DEACTIVATED };
 uint32_t iconHeight = 32;
 uint32_t iconWidth = 32;
 
 CPluginMimeFilterClient* CPluginClass::s_mimeFilter = NULL;
 
 CLOSETHEMEDATA pfnClose = NULL;
 DRAWTHEMEBACKGROUND pfnDrawThemeBackground = NULL;
 OPENTHEMEDATA pfnOpenThemeData = NULL;
 
 ATOM CPluginClass::s_atomPaneClass = NULL;
 HINSTANCE CPluginClass::s_hUxtheme = NULL;
 SyncSet<CPluginClass*, nullptr> instanceSet;
-std::map<DWORD, CPluginClass*> CPluginClass::s_threadInstances;
 
 CComAutoCriticalSection CPluginClass::s_criticalSectionLocal;
 CComAutoCriticalSection CPluginClass::s_criticalSectionWindow;
+
+namespace
+{
+  /**
+   * A synchronized map whose key is always the current thread ID.
+   */
+  class CurrentThreadMap
+    : public SyncMap<DWORD, CPluginClass*, nullptr>
+  {
+    typedef SyncMap<DWORD, CPluginClass*, nullptr> Base;
+
+  public:
+    bool AddIfAbsent(CPluginClass* p)
+    {
+      return Base::AddIfAbsent(::GetCurrentThreadId(), p);
+    }
+
+    bool RemoveAndCheck()
+    {
+      return Base::RemoveIfPresent(::GetCurrentThreadId());
+    }
+
+    CPluginClass* Locate()
+    {
+      return Base::Locate(::GetCurrentThreadId());
+    }
+  };
+
+  /**
+   * Map from thread ID's to CPluginClass instances
+   */
+  CurrentThreadMap threadMap;
+}
 
 /*
  * Without namespace declaration, the identifier "Rectangle" is ambiguous
  * See http://msdn.microsoft.com/en-us/library/windows/desktop/dd162898(v=vs.85).aspx
  */
 namespace AdblockPlus
 {
   /**
     * Replacement for ATL type CRect.
     */
   class Rectangle
     : public RECT
   {
   public:
-    int Height() const
-    {
-      return bottom - top;
-    }
-
-    int Width() const
-    {
-      return right - left;
+    unsigned long Height() const
+    {
+      if (bottom < top)
+      {
+        throw std::runtime_error("invariant violation: rectangle bottom < top");
+      }
+      return static_cast<unsigned long>(bottom - top);
+    }
+
+    unsigned long Width() const
+    {
+      if (right < left)
+      {
+        throw std::runtime_error("invariant violation: rectangle right < left");
+      }
+      return static_cast<unsigned long>(right - left);
     }
   };
 }
 
 /**
  * Wrapper class for a browser site object that ensures proper site life cycle.
  *
  * The browser is guaranteed to be valid for the lifetime of the object.
  * What that means is that SetSite(0) on the containing BHO instance will not return before this object is destroyed.
  * This property avoids a race condition where one thread is using a browser site for services while IE is simultaneously shutting it down.
@@ skipping 51 matching lines @@
       });
     if (!instance)
     {
       browser = nullptr;
     }
     else
     {
       browser = instance->m_webBrowser2;
       if (!browser)
       {
-        throw std::logic_error("Instance without site found in set of instances with site");

[sergei, 2016/01/04 15:34:31]

"... where site is a browser (IWebBrowser2) and instance refers to an instance
of CPluginClass". Otherwise this message is completely unclear. Image that you
encountered it in a log.

[Eric, 2016/01/04 17:49:20]

When I encounter such messages in a log, I immediately use 'grep' to search the
source code for the occurrence of the statement. The exact text doesn't need to
be extensive.

More importantly, though, it's a 'logic_error', which means that your code has a
defect if it ever throws at all. If you find such a message in a log, you've got
bigger problems.

I have clarified the message, not to talk about specific classes, but to more
clearly explain the invariant that is violated if reached here.

+        throw std::logic_error("invariant violation: BHO instance without site found in a set of instances each of which must have a current site");
       }
     }
   };
   
   /**
    * Destructor releases any lock held and allows SetSite() to complete.
    */
   ~AnyCurrentSiteBrowser() {}; // = default
 
   IWebBrowser2* operator->() const
   {
     return browser;
   }
 
   operator IWebBrowser2*() const
   {
     return browser;
   }
 
   operator bool() const
   {
     return browser != nullptr;
   }
 };
 
 CPluginClass::CPluginClass()
   : m_webBrowser2(nullptr)
 {
+  DEBUG_GENERAL([this]() -> std::wstring
+    {
+      std::wstring s = L"CPluginClass::<constructor>, this = ";
+      s += ToHexLiteral(this);
+      return s;
+    }());
+
   //Use this line to debug memory leaks
   //    _CrtDumpMemoryLeaks();
 
   m_isAdvised = false;
   m_hTabWnd = NULL;
   m_hStatusBarWnd = NULL;
   m_hPaneWnd = NULL;
   m_nPaneWidth = 0;
   m_pWndProcStatus = NULL;
   m_hTheme = NULL;
   m_isInitializedOk = false;
-
-
-  m_tab = new CPluginTab(this);
-
+  m_tab = new CPluginTab();
   Dictionary::Create(GetBrowserLanguage());
 }
 
 CPluginClass::~CPluginClass()
 {
+  DEBUG_GENERAL([this]() -> std::wstring
+    {
+      std::wstring s = L"CPluginClass::<destructor>, this = ";
+      s += ToHexLiteral(this);
+      return s;
+    }());
+
   delete m_tab;
 }
 
 HWND CPluginClass::GetBrowserHWND() const
 {
   if (!m_webBrowser2)
   {
     DEBUG_ERROR_LOG(0, 0, 0, "CPluginClass::GetBrowserHWND - Reached with m_webBrowser2 == nullptr");
     return nullptr;
   }
@@ skipping 11 matching lines @@
 {
   return m_webBrowser2.IsEqualObject(otherBrowser);
 }
 
 std::wstring CPluginClass::GetBrowserUrl() const
 {
   std::wstring url;
   if (m_webBrowser2)
   {
     CComBSTR bstrURL;
-    if (SUCCEEDED(m_webBrowser2->get_LocationURL(&bstrURL)) && bstrURL)
-    {
-      url = std::wstring(bstrURL, SysStringLen(bstrURL));
+    if (SUCCEEDED(m_webBrowser2->get_LocationURL(&bstrURL)))
+    {
+      url = ToWstring(bstrURL);
     }
   }
   else
   {
-    DEBUG_ERROR_LOG(0, 0, 0, "CPluginClass::GetBrowserUrl - Reached with m_webBrowser2 == nullptr");
+    DEBUG_GENERAL(L"CPluginClass::GetBrowserUrl - Reached with m_webBrowser2 == nullptr (probable invariant violation)");
+  }
+  if (url.empty())
+  {
     url = m_tab->GetDocumentUrl();
   }
   return url;
 }
 
 DWORD WINAPI CPluginClass::StartInitObject(LPVOID thisPtr)
 {
   if (thisPtr == NULL)
     return 0;
   if (!((CPluginClass*)thisPtr)->InitObject())
@@ skipping 15 matching lines @@
  * but it is not a proper substitute for one.
  */
 STDMETHODIMP CPluginClass::SetSite(IUnknown* unknownSite)
 {
   try
   {
     std::lock_guard<std::mutex> lock(siteGuard);
 
     if (unknownSite)
     {
-
-      DEBUG_GENERAL(L"================================================================================\nNEW TAB UI\n================================================================================")
+      DEBUG_GENERAL(L"================================================================================\nNEW TAB UI\n================================================================================");
 
       HRESULT hr = ::CoInitialize(NULL);
       if (FAILED(hr))
       {
         DEBUG_ERROR_LOG(hr, PLUGIN_ERROR_SET_SITE, PLUGIN_ERROR_SET_SITE_COINIT, "Class::SetSite - CoInitialize");
       }
 
       /*
        * We were instantiated as a BHO, so our site is always of type IWebBrowser2.
        */
       m_webBrowser2 = ATL::CComQIPtr<IWebBrowser2>(unknownSite);
       if (!m_webBrowser2)
       {
         throw std::logic_error("CPluginClass::SetSite - Unable to convert site pointer to IWebBrowser2*");
       }
+      DEBUG_GENERAL([this]() -> std::wstring
+        {
+          std::wstringstream ss;
+          ss << L"CPluginClass::SetSite, this = " << ToHexLiteral(this);
+          ss << L", browser = " << ToHexLiteral(m_webBrowser2);
+          return ss.str();
+        }());
+
+      /*
+       * Add ourselves to the thread map.
+       */
+      if (!threadMap.AddIfAbsent(this))
+      {
+        throw std::logic_error("CPluginClass::SetSite - May not overwrite existing entry in thread map");
+      }
       if (!instanceSet.InsertIfAbsent(this))

[sergei, 2016/01/04 15:34:31]

I would like to have `assert`s in addition to throwing of exceptions here and
below, otherwise the exceptions are silently eaten and we won't know about a
trouble.

[Eric, 2016/01/04 17:49:20]

'assert' is a C mechanism, and it's only active during debug.

This is very consciously a 'throw' here. While we currently have no capability
of logging in Release builds, this is the kind of exception that we want to log
to the Windows Error Reporting facility. We don't have code for that, yet.

If you want to catch them, set up Visual Studio to do so. In
Debug/Windows/Exceptions Settings, add "std::logic_error" to the list called
"Break When Thrown".

[sergei, 2016/01/29 15:28:56]

`assert` is also C++ mechanism. Yes, it's active only during debugging because
its main aim is to notify the developer about an issue. I'm not suggesting to
replace throwing, but add `assert` in addition.
That's very inconvenient because of too many false positives. I could use a
special Visual Studio profile only for adblockplusie project, but it's really
not friendly for anybody else.

[Eric, 2016/01/29 16:16:12]

You're advocating code bloat for zero-to-minimal benefit.

The presence of this check here in 'SetSite()' is purely defensive. IE creates a
new thread for each BHO instance.

Request add 'assert' here rejected.

       {
         throw std::logic_error("CPluginClass::SetSite - May not overwrite existing entry in instance set");
       }
+
 
       //register the mimefilter
       //and only mimefilter
       //on some few computers the mimefilter does not get properly registered when it is done on another thread
       s_criticalSectionLocal.Lock();
       {
         s_mimeFilter = CPluginClientFactory::GetMimeFilterClientInstance();
       }
       s_criticalSectionLocal.Unlock();
 
       try
       {
-        DEBUG_GENERAL("Loaded as BHO");
         HRESULT hr = DispEventAdvise(m_webBrowser2);
         if (SUCCEEDED(hr))
         {
           m_isAdvised = true;
           try
           {
             std::thread startInitObjectThread(StartInitObject, this);
             startInitObjectThread.detach(); // TODO: but actually we should wait for the thread in the dtr.
           }
           catch (const std::system_error& ex)
           {
             DEBUG_SYSTEM_EXCEPTION(ex, PLUGIN_ERROR_THREAD, PLUGIN_ERROR_MAIN_THREAD_CREATE_PROCESS, 
               "Class::Thread - Failed to create StartInitObject thread");
           }
         }
         else
         {
           DEBUG_ERROR_LOG(hr, PLUGIN_ERROR_SET_SITE, PLUGIN_ERROR_SET_SITE_ADVICE, "Class::SetSite - Advise");
         }
       }
       catch (const std::runtime_error& ex)
       {
         DEBUG_EXCEPTION(ex);
         Unadvise();
       }
     }
     else
     {
+      DEBUG_GENERAL([this]() -> std::wstring
+      {
+        std::wstringstream ss;
+        ss << L"CPluginClass::SetSite, this = " << ToHexLiteral(this);
+        ss << L", browser = nullptr";
+        return ss.str();
+      }());
+
       Unadvise();
 
       // Destroy window
       if (m_pWndProcStatus)
       {
         ::SetWindowLongPtr(m_hStatusBarWnd, GWLP_WNDPROC, (LPARAM)(WNDPROC)m_pWndProcStatus);
 
         m_pWndProcStatus = NULL;
       }
 
       if (m_hPaneWnd)
       {
         DestroyWindow(m_hPaneWnd);
         m_hPaneWnd = NULL;
       }
 
       m_hTabWnd = NULL;
       m_hStatusBarWnd = NULL;
 
       // Remove instance from the list, shutdown threads
       HANDLE hMainThread = NULL;
       HANDLE hTabThread = NULL;
 
       if (!instanceSet.EraseWithCheck(this))
       {
         throw std::logic_error("CPluginClass::SetSite - Missing entry in instance set");
+      }
+      if (!threadMap.RemoveAndCheck())
+      {
+        throw std::logic_error("CPluginClass::SetSite - Missing entry in thread map");
       }
       s_criticalSectionLocal.Lock();
       {
         if (instanceSet.Empty())
         {
           // TODO: Explicitly releasing a resource when a container becomes empty looks like a job better suited for shared_ptr
           CPluginClientFactory::ReleaseMimeFilterClientInstance();
         }
       }
       s_criticalSectionLocal.Unlock();
@@ skipping 152 matching lines @@
   {
     ATL::CComQIPtr<IWebBrowser2> webBrowser = frameBrowserDisp;
     if (!webBrowser)
     {
       return;
     }
     if (!urlVariant || urlVariant->vt != VT_BSTR)
     {
       return;
     }
-    std::wstring url(urlVariant->bstrVal, SysStringLen(urlVariant->bstrVal));
+    std::wstring url = ToWstring(urlVariant->bstrVal);
 
     // If webbrowser2 is equal to top level browser (as set in SetSite), we are
     // navigating new page
     CPluginClient* client = CPluginClient::GetInstance();
     if (url.find(L"javascript") == 0)
     {
     }
     else if (IsRootBrowser(webBrowser))
     {
       m_tab->OnNavigate(url);
@@ skipping 58 matching lines @@
 // Entry point
 void STDMETHODCALLTYPE CPluginClass::OnWindowStateChanged(unsigned long flags, unsigned long validFlagsMask)
 {
   try
   {
     DEBUG_GENERAL(L"WindowStateChanged (check tab changed)");
     bool newtabshown = validFlagsMask == (OLECMDIDF_WINDOWSTATE_USERVISIBLE | OLECMDIDF_WINDOWSTATE_ENABLED)
       && flags == (OLECMDIDF_WINDOWSTATE_USERVISIBLE | OLECMDIDF_WINDOWSTATE_ENABLED);
     if (newtabshown)
     {
-      std::map<DWORD,CPluginClass*>::const_iterator it = s_threadInstances.find(GetCurrentThreadId());
-      if (it == s_threadInstances.end())
-      {
-        s_threadInstances[::GetCurrentThreadId()] = this;
-        if (!m_isInitializedOk)
-        {
-          m_isInitializedOk = true;
-          InitObject();
-          UpdateStatusBar();
-        }
+      if (!m_isInitializedOk)
+      {
+        m_isInitializedOk = true;
+        InitObject();
+        UpdateStatusBar();
       }
     }
     notificationMessage.Hide();
     DEBUG_GENERAL(L"WindowStateChanged (check tab changed) end");
   }
   catch (...)
   {
   }
 }
 
@@ skipping 376 matching lines @@
     {
       return p->m_hStatusBarWnd == hStatusBarWnd;
     });
 }
 
 CPluginTab* CPluginClass::GetTab()
 {
   return m_tab;
 }
 
-CPluginTab* CPluginClass::GetTab(DWORD dwThreadId)
-{
-  CPluginTab* tab = NULL;
-
-  s_criticalSectionLocal.Lock();
-  {
-    std::map<DWORD,CPluginClass*>::const_iterator it = s_threadInstances.find(dwThreadId);
-    if (it != s_threadInstances.end())
-    {
-      tab = it->second->m_tab;
-    }
-  }
-  s_criticalSectionLocal.Unlock();
-
-  return tab;
-}
-
-
+CPluginTab* CPluginClass::GetTabForCurrentThread()
+{
+  auto p = threadMap.Locate();
+  return p ? p->m_tab : nullptr;
+}
+
+// Entry point
 STDMETHODIMP CPluginClass::QueryStatus(const GUID* pguidCmdGroup, ULONG cCmds, OLECMD prgCmds[], OLECMDTEXT* pCmdText)
 {
-  if (cCmds == 0) return E_INVALIDARG;
-  if (prgCmds == 0) return E_POINTER;
-
-  prgCmds[0].cmdf = OLECMDF_ENABLED;
-
+  try
+  {
+    if (cCmds == 0) return E_INVALIDARG;
+    if (prgCmds == 0) return E_POINTER;
+
+    prgCmds[0].cmdf = OLECMDF_ENABLED;
+  }
+  catch (...)
+  {
+    DEBUG_GENERAL(L"CPluginClass::QueryStatus - exception");
+    return E_FAIL;
+  }
   return S_OK;
 }
 
 HMENU CPluginClass::CreatePluginMenu(const std::wstring& url)
 {
   DEBUG_GENERAL("CreatePluginMenu");
   HINSTANCE hInstance = _AtlBaseModule.GetModuleInstance();
 
   HMENU hMenu = ::LoadMenu(hInstance, MAKEINTRESOURCE(IDR_MENU1));
 
@@ skipping 65 matching lines @@
           s_mimeFilter = NULL;
 
           CPluginClientFactory::ReleaseMimeFilterClientInstance();
         }
       }
       s_criticalSectionLocal.Unlock();
     }
     break;
   case ID_MENU_SETTINGS:
     {
       AnyCurrentSiteBrowser browser;

[sergei, 2016/01/04 15:34:31]

Why can we not use `m_webBrowser2` here? When can it be called not between
SetSite(not nullptr) and SetSite(nullptr)?

[sergei, 2016/01/29 15:28:56]

Not answered.

[Eric, 2016/01/29 16:16:12]

This function can be called from a worker thread which is not associated with
any BHO at all.
These worker threads never call 'SetSite()' at all. (And it's never the case
that any single thread is ever reused for a second BHO instance, although that's
not particularly relevant here.)

The race condition is that we have events registered in such a way that it's
possible that a call appear here in one thread (a worker thread) where another
thread has already called 'SetSite(nullptr)' on the thread associated with this
BHO instance. Hence it's possible for 
'm_webBrowser2' to be null here.

What you're observing here is a consequence of some really awful (and quite old)
implementation decisions about 'CPluginClass'. It is handling both BHO instances
as well as UI events. They really should never have been combined into a single
class in the first place. Regardless of the past, if the UI event handlers were
in a separate class, then 'AnyCurrentSiteBrowser' is how such a class would get
a browser pointer to call 'Navigate()' on.

[Eric, 2016/01/29 16:16:12]

Sorry. Must have missed it earlier.

       if (browser)
       {
         NavigateNewTab(browser, UserSettingsFileUrl());
       }
     }
     break;
   case ID_MENU_DISABLE_ON_SITE:
     {
       std::wstring urlString = GetTab()->GetDocumentUrl();
       std::string filterText = client->GetWhitelistingFilter(urlString);
@@ skipping 27 matching lines @@
 
   MENUITEMINFOW miiSep = {};
   miiSep.cbSize = sizeof(miiSep);
   miiSep.fMask = MIIM_TYPE | MIIM_FTYPE;
   miiSep.fType = MFT_SEPARATOR;
 
   CPluginClient* client = CPluginClient::GetInstance();
   CPluginSettings* settings = CPluginSettings::GetInstance();
   {
     ctext = dictionary->Lookup("menu", "menu-disable-on-site");
-    // Is domain in white list?
     ReplaceString(ctext, L"?1?", client->GetHostFromUrl(url));
-    if (client->IsWhitelistedUrl(GetTab()->GetDocumentUrl()))
-    {
+    /*
+     * The display state of the "disable on this site" menu item depends upon tab content
+     */
+    if (!GetTab()->IsPossibleToDisableOnSite())
+    {
+      // Since we can't disable the present content,
+      // it makes no sense to offer the user an option to block it.
+      fmii.fState = MFS_UNCHECKED | MFS_DISABLED;
+    }
+    else if (client->IsWhitelistedUrl(GetTab()->GetDocumentUrl()))
+    {
+      // Domain is in white list, indicated by a check mark
       fmii.fState = MFS_CHECKED | MFS_ENABLED;
     }
     else
     {
       fmii.fState = MFS_UNCHECKED | MFS_ENABLED;
     }
     fmii.fMask = MIIM_STRING | MIIM_STATE;
     fmii.dwTypeData = const_cast<LPWSTR>(ctext.c_str());
     fmii.cch = static_cast<UINT>(ctext.size());
 
@@ skipping 28 matching lines @@
   ctext = dictionary->Lookup("menu", "menu-settings");
   fmii.fMask  = MIIM_STATE | MIIM_STRING;
   fmii.fState = MFS_ENABLED;
   fmii.dwTypeData = const_cast<LPWSTR>(ctext.c_str());
   fmii.cch = static_cast<UINT>(ctext.size());
   ::SetMenuItemInfoW(hMenu, ID_MENU_SETTINGS, FALSE, &fmii);
 
   return true;
 }
 
-
+// Entry point
 STDMETHODIMP CPluginClass::Exec(const GUID*, DWORD nCmdID, DWORD, VARIANTARG*, VARIANTARG*)
 {
-  HWND hBrowserWnd = GetBrowserHWND();
-  if (!hBrowserWnd)
-  {
-    return E_FAIL;
-  }
-
-  // Create menu
-  HMENU hMenu = CreatePluginMenu(m_tab->GetDocumentUrl());
-  if (!hMenu)
-  {
-    return E_FAIL;
-  }
-
-  // Check if button in toolbar was pressed
-  int nIDCommand = -1;
-  BOOL bRightAlign = FALSE;
-
-  POINT pt;
-  GetCursorPos(&pt);
-
-  HWND hWndToolBar = ::WindowFromPoint(pt);
-
-  DWORD nProcessId;
-  ::GetWindowThreadProcessId(hWndToolBar, &nProcessId);
-
-  if (hWndToolBar && ::GetCurrentProcessId() == nProcessId)
-  {
-    ::ScreenToClient(hWndToolBar, &pt);
-    int nButton = (int)::SendMessage(hWndToolBar, TB_HITTEST, 0, (LPARAM)&pt);
-
-    if (nButton > 0)
-    {
-      TBBUTTON pTBBtn = {};
-
-      if (SendMessage(hWndToolBar, TB_GETBUTTON, nButton, (LPARAM)&pTBBtn))
-      {
-        RECT rcButton;
-        nIDCommand = pTBBtn.idCommand;
-
-        if (SendMessage(hWndToolBar, TB_GETRECT, nIDCommand, (LPARAM)&rcButton))
-        {
-          pt.x = rcButton.left;
-          pt.y = rcButton.bottom;
-          ClientToScreen(hWndToolBar, &pt);
-
-          RECT rcWorkArea;
-          SystemParametersInfo(SPI_GETWORKAREA, 0, (LPVOID)&rcWorkArea, 0);
-          if (rcWorkArea.right - pt.x < 150)
+  try
+  {
+    HWND hBrowserWnd = GetBrowserHWND();
+    if (!hBrowserWnd)
+    {
+      return E_FAIL;
+    }
+
+    // Create menu
+    HMENU hMenu = CreatePluginMenu(m_tab->GetDocumentUrl());
+    if (!hMenu)
+    {
+      return E_FAIL;
+    }
+
+    // Check if button in toolbar was pressed
+    int nIDCommand = -1;
+    BOOL bRightAlign = FALSE;
+
+    POINT pt;
+    GetCursorPos(&pt);
+
+    HWND hWndToolBar = ::WindowFromPoint(pt);
+
+    DWORD nProcessId;
+    ::GetWindowThreadProcessId(hWndToolBar, &nProcessId);
+
+    if (hWndToolBar && ::GetCurrentProcessId() == nProcessId)
+    {
+      ::ScreenToClient(hWndToolBar, &pt);
+      int nButton = (int)::SendMessage(hWndToolBar, TB_HITTEST, 0, (LPARAM)&pt);
+
+      if (nButton > 0)
+      {
+        TBBUTTON pTBBtn = {};
+
+        if (SendMessage(hWndToolBar, TB_GETBUTTON, nButton, (LPARAM)&pTBBtn))
+        {
+          RECT rcButton;
+          nIDCommand = pTBBtn.idCommand;
+
+          if (SendMessage(hWndToolBar, TB_GETRECT, nIDCommand, (LPARAM)&rcButton))
           {
-            bRightAlign = TRUE;
-            pt.x = rcButton.right;
+            pt.x = rcButton.left;
             pt.y = rcButton.bottom;
             ClientToScreen(hWndToolBar, &pt);
+
+            RECT rcWorkArea;
+            SystemParametersInfo(SPI_GETWORKAREA, 0, (LPVOID)&rcWorkArea, 0);
+            if (rcWorkArea.right - pt.x < 150)
+            {
+              bRightAlign = TRUE;
+              pt.x = rcButton.right;
+              pt.y = rcButton.bottom;
+              ClientToScreen(hWndToolBar, &pt);
+            }
           }
         }
       }
+      else
+      {
+        GetCursorPos(&pt);
+      }
+    }
+
+    // Display menu
+    UINT nFlags = 0;
+    if (bRightAlign)
+    {
+      nFlags |= TPM_RIGHTALIGN;
     }
     else
     {
-      GetCursorPos(&pt);
-    }
-  }
-
-  // Display menu
-  UINT nFlags = 0;
-  if (bRightAlign)
-  {
-    nFlags |= TPM_RIGHTALIGN;
-  }
-  else
-  {
-    nFlags |= TPM_LEFTALIGN;
-  }
-
-  DisplayPluginMenu(hMenu, nIDCommand, pt, nFlags);
+      nFlags |= TPM_LEFTALIGN;
+    }
+
+    DisplayPluginMenu(hMenu, nIDCommand, pt, nFlags);
+  }
+  catch (...)
+  {
+    // Suppress exception, log only
+    DEBUG_GENERAL(L"CPluginClass::Exec - exception");
+    return E_FAIL;
+  }
 
   return S_OK;
 }
 
-/////////////////////////////////////////////////////////////////////////////
-// Window procedures
-
+// Entry point
 LRESULT CALLBACK CPluginClass::NewStatusProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
 {
-  // Find tab
-  CPluginClass *pClass = FindInstance(hWnd);
-  if (!pClass)
-  {
-    return DefWindowProc(hWnd, message, wParam, lParam);
-  }
-
-  // Process message
-  switch (message)
-  {
-  case SB_SIMPLE:
-    {
-      ShowWindow(pClass->m_hPaneWnd, !wParam);
+  CPluginClass *pClass;
+  try
+  {
+    // Find tab
+    pClass = FindInstance(hWnd);
+    if (!pClass)
+    {
+      /*
+       * Race condition if reached.
+       * We did not unhook the window procedure for the status bar when the last BHO instance using it terminated.
+       * The next best thing is to call the system default window function.
+       */
+      return DefWindowProc(hWnd, message, wParam, lParam);
+    }
+
+    // Process message
+    switch (message)
+    {
+    case SB_SIMPLE:
+      {
+        ShowWindow(pClass->m_hPaneWnd, !wParam);
+        break;
+      }
+
+    case WM_SYSCOLORCHANGE:
+      {
+        pClass->UpdateTheme();
+        break;
+      }
+
+    case SB_SETPARTS:
+      {
+        if (!lParam || !wParam || wParam > 30 || !IsWindow(pClass->m_hPaneWnd))
+        {
+          return CallWindowProc(pClass->m_pWndProcStatus, hWnd, message, wParam, lParam);
+        }
+
+        WPARAM nParts = wParam;
+        if (STATUSBAR_PANE_NUMBER >= nParts)
+        {
+          return CallWindowProc(pClass->m_pWndProcStatus, hWnd, message, wParam, lParam);
+        }
+
+        HLOCAL hLocal = LocalAlloc(LHND, sizeof(int) * (nParts + 1));
+        LPINT lpParts = (LPINT)LocalLock(hLocal);
+        memcpy(lpParts, (void*)lParam, wParam*sizeof(int));
+
+        for (unsigned i = 0; i < STATUSBAR_PANE_NUMBER; i++)
+        {
+          lpParts[i] -= pClass->m_nPaneWidth;
+        }
+        LRESULT hRet = CallWindowProc(pClass->m_pWndProcStatus, hWnd, message, wParam, (LPARAM)lpParts);
+
+        AdblockPlus::Rectangle rcPane;
+        ::SendMessage(hWnd, SB_GETRECT, STATUSBAR_PANE_NUMBER, (LPARAM)&rcPane);
+
+        AdblockPlus::Rectangle rcClient;
+        ::GetClientRect(hWnd, &rcClient);
+
+        ::MoveWindow(
+          pClass->m_hPaneWnd,
+          lpParts[STATUSBAR_PANE_NUMBER] - pClass->m_nPaneWidth,
+          0,
+          pClass->m_nPaneWidth,
+          rcClient.Height(),
+          TRUE);
+
+        ::LocalFree(hLocal);
+        return hRet;
+      }
+
+    default:
       break;
     }
-
-  case WM_SYSCOLORCHANGE:
-    {
-      pClass->UpdateTheme();
-      break;
-    }
-
-  case SB_SETPARTS:
-    {
-      if (!lParam || !wParam || wParam > 30 || !IsWindow(pClass->m_hPaneWnd))
-      {
-        return CallWindowProc(pClass->m_pWndProcStatus, hWnd, message, wParam, lParam);
-      }
-
-      WPARAM nParts = wParam;
-      if (STATUSBAR_PANE_NUMBER >= nParts)
-      {
-        return CallWindowProc(pClass->m_pWndProcStatus, hWnd, message, wParam, lParam);
-      }
-
-      HLOCAL hLocal = LocalAlloc(LHND, sizeof(int) * (nParts+1));
-      LPINT lpParts = (LPINT)LocalLock(hLocal);
-      memcpy(lpParts, (void*)lParam, wParam*sizeof(int));
-
-      for (unsigned i = 0; i < STATUSBAR_PANE_NUMBER; i++)
-      {
-        lpParts[i] -= pClass->m_nPaneWidth;
-      }
-      LRESULT hRet = CallWindowProc(pClass->m_pWndProcStatus, hWnd, message, wParam, (LPARAM)lpParts);
-
-      AdblockPlus::Rectangle rcPane;
-      ::SendMessage(hWnd, SB_GETRECT, STATUSBAR_PANE_NUMBER, (LPARAM)&rcPane);
-
-      AdblockPlus::Rectangle rcClient;
-      ::GetClientRect(hWnd, &rcClient);
-
-      ::MoveWindow(
-        pClass->m_hPaneWnd,
-        lpParts[STATUSBAR_PANE_NUMBER] - pClass->m_nPaneWidth,
-        0,
-        pClass->m_nPaneWidth,
-        rcClient.Height(),
-        TRUE);
-
-      ::LocalFree(hLocal);
-
-
-      return hRet;
-    }
-
-  default:
-    break;
-  }
-
-  LRESULT result = CallWindowProc(pClass->m_pWndProcStatus, hWnd, message, wParam, lParam);
-
-
-  return result;
-
+  }
+  catch (...)
+  {
+    // Suppress exception. Fall through to default handler.
+    DEBUG_GENERAL(L"CPluginClass::NewStatusProc - exception");
+  }
+  return ::CallWindowProc(pClass->m_pWndProcStatus, hWnd, message, wParam, lParam);
 }
 
 
 HICON CPluginClass::GetStatusBarIcon(const std::wstring& url)
 {
   // use the disable icon as defualt, if the client doesn't exists
   HICON hIcon = GetIcon(ICON_PLUGIN_DEACTIVATED);
 
-  CPluginTab* tab = GetTab(::GetCurrentThreadId());
+  CPluginTab* tab = GetTabForCurrentThread();
   if (tab)
   {
     CPluginClient* client = CPluginClient::GetInstance();
     if (CPluginSettings::GetInstance()->IsPluginEnabled())
     {
       if (client->IsWhitelistedUrl(url))
       {
         hIcon = GetIcon(ICON_PLUGIN_DISABLED);
       }
       else
       {
         CPluginSettings* settings = CPluginSettings::GetInstance();
         hIcon = GetIcon(ICON_PLUGIN_ENABLED);
       }
     }
   }
   return hIcon;
 }
 
-
+// Entry point
 LRESULT CALLBACK CPluginClass::PaneWindowProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
 {
-  // Find tab
-  CPluginClass *pClass = FindInstance(GetParent(hWnd));
-  if (!pClass)
-  {
-    return ::DefWindowProc(hWnd, message, wParam, lParam);
-  }
-
-  // Process message
-  switch (message)
-  {
-
-  case WM_SETCURSOR:
-    {
-      ::SetCursor(::LoadCursor(NULL, IDC_ARROW));
-      return TRUE;
-    }
-  case WM_PAINT:
-    {
-      PAINTSTRUCT ps;
-      HDC hDC = ::BeginPaint(hWnd, &ps);
-
-      AdblockPlus::Rectangle rcClient;
-      ::GetClientRect(hWnd, &rcClient);
-
-      int nDrawEdge = 0;
-
-      // Old Windows background drawing
-      if (pClass->m_hTheme == NULL)
-      {
-        ::FillRect(hDC, &rcClient, (HBRUSH)(COLOR_BTNFACE + 1));
-        ::DrawEdge(hDC, &rcClient, BDR_RAISEDINNER, BF_LEFT);
-
-        nDrawEdge = 3;
-        rcClient.left += 3;
-
-        ::DrawEdge(hDC, &rcClient, BDR_SUNKENOUTER, BF_RECT);
-      }
-      // Themed background drawing
-      else
-      {
-        // Draw background
-        if (pfnDrawThemeBackground)
-        {
-          AdblockPlus::Rectangle rc = rcClient;
-          rc.right -= 2;
-          pfnDrawThemeBackground(pClass->m_hTheme, hDC, 0, 0, &rc, NULL);
-        }
-
-        // Copy separator picture to left side
-        int nHeight = rcClient.Height();
-        int nWidth = rcClient.Width() - 2;
-
-        for (int i = 0; i < 2; i++)
-        {
-          for (int j = 0; j < nHeight; j++)
+  try
+  {
+    // Find tab
+    CPluginClass *pClass = FindInstance(GetParent(hWnd));
+    if (!pClass)
+    {
+      return ::DefWindowProc(hWnd, message, wParam, lParam);
+    }
+
+    // Process message
+    switch (message)
+    {
+    case WM_SETCURSOR:
+      {
+        ::SetCursor(::LoadCursor(NULL, IDC_ARROW));
+        return TRUE;
+      }
+    case WM_PAINT:
+      {
+        PAINTSTRUCT ps;
+        HDC hDC = ::BeginPaint(hWnd, &ps);
+
+        AdblockPlus::Rectangle rcClient;
+        ::GetClientRect(hWnd, &rcClient);
+
+        int nDrawEdge = 0;
+
+        // Old Windows background drawing
+        if (pClass->m_hTheme == NULL)
+        {
+          ::FillRect(hDC, &rcClient, (HBRUSH)(COLOR_BTNFACE + 1));
+          ::DrawEdge(hDC, &rcClient, BDR_RAISEDINNER, BF_LEFT);
+
+          nDrawEdge = 3;
+          rcClient.left += 3;
+
+          ::DrawEdge(hDC, &rcClient, BDR_SUNKENOUTER, BF_RECT);
+        }
+        // Themed background drawing
+        else
+        {
+          // Draw background
+          if (pfnDrawThemeBackground)
           {
-            COLORREF clr = ::GetPixel(hDC, i + nWidth, j);
-
-            // Ignore black boxes (if source is obscured by other windows)
-            if (clr != -1 && (GetRValue(clr) > 8 || GetGValue(clr) > 8 || GetBValue(clr) > 8))
+            AdblockPlus::Rectangle rc = rcClient;
+            rc.right -= 2;
+            pfnDrawThemeBackground(pClass->m_hTheme, hDC, 0, 0, &rc, NULL);
+          }
+
+          // Copy separator picture to left side
+          int nHeight = rcClient.Height();
+          int nWidth = rcClient.Width() - 2;
+
+          for (int i = 0; i < 2; i++)
+          {
+            for (int j = 0; j < nHeight; j++)
             {
-              ::SetPixel(hDC, i, j, clr);
+              COLORREF clr = ::GetPixel(hDC, i + nWidth, j);
+
+              // Ignore black boxes (if source is obscured by other windows)
+              if (clr != -1 && (GetRValue(clr) > 8 || GetGValue(clr) > 8 || GetBValue(clr) > 8))
+              {
+                ::SetPixel(hDC, i, j, clr);
+              }
             }
           }
         }
-      }
-
-      // Draw icon
-      if (CPluginClient::GetInstance())
-      {
-        HICON hIcon = GetStatusBarIcon(pClass->GetTab()->GetDocumentUrl());
-
-        int offx = nDrawEdge;
-        if (hIcon)
-        {
-          //Get the RECT for the leftmost pane (the status text pane)
+
+        // Draw icon
+        if (CPluginClient::GetInstance())
+        {
+          HICON hIcon = GetStatusBarIcon(pClass->GetTab()->GetDocumentUrl());
+
+          int offx = nDrawEdge;
+          if (hIcon)
+          {
+            //Get the RECT for the leftmost pane (the status text pane)
+            RECT rect;
+            BOOL rectRes = ::SendMessage(pClass->m_hStatusBarWnd, SB_GETRECT, 0, (LPARAM)&rect);
+            ::DrawIconEx(hDC, 0, rect.bottom - rect.top - iconHeight, hIcon, iconWidth, iconHeight, NULL, NULL, DI_NORMAL);
+            offx += iconWidth;
+          }
+#ifdef _DEBUG
+          // Display version
+          HFONT hFont = (HFONT)::SendMessage(pClass->m_hStatusBarWnd, WM_GETFONT, 0, 0);
+          HGDIOBJ hOldFont = ::SelectObject(hDC, hFont);
+
+          AdblockPlus::Rectangle rcText = rcClient;
+          rcText.left += offx;
+          ::SetBkMode(hDC, TRANSPARENT);
+          ::DrawTextW(hDC, IEPLUGIN_VERSION, -1, &rcText, DT_WORD_ELLIPSIS | DT_LEFT | DT_SINGLELINE | DT_VCENTER);
+
+          ::SelectObject(hDC, hOldFont);
+#endif // _DEBUG
+        }
+
+        // Done!
+        EndPaint(hWnd, &ps);
+
+        return 0;
+      }
+
+    case WM_LBUTTONUP:
+    case WM_RBUTTONUP:
+      {
+        std::wstring url = pClass->GetBrowserUrl();
+        if (url != pClass->GetTab()->GetDocumentUrl())
+        {
+          pClass->GetTab()->SetDocumentUrl(url);
+        }
+
+        // Create menu
+        HMENU hMenu = pClass->CreatePluginMenu(url);
+        if (!hMenu)
+        {
+          return 0;
+        }
+
+        // Display menu
+        POINT pt;
+        ::GetCursorPos(&pt);
+
+        RECT rc;
+        ::GetWindowRect(hWnd, &rc);
+
+        if (rc.left >= 0 && rc.top >= 0)
+        {
+          pt.x = rc.left;
+          pt.y = rc.top;
+        }
+
+        pClass->DisplayPluginMenu(hMenu, -1, pt, TPM_LEFTALIGN | TPM_BOTTOMALIGN);
+        break;
+      }
+    case WM_DESTROY:
+      break;
+    case SC_CLOSE:
+      break;
+
+    case WM_UPDATEUISTATE:
+      {
+        CPluginTab* tab = GetTabForCurrentThread();
+        if (tab)
+        {
+          tab->OnActivate();
           RECT rect;
-          BOOL rectRes = ::SendMessage(pClass->m_hStatusBarWnd, SB_GETRECT, 0, (LPARAM)&rect);
-          ::DrawIconEx(hDC, 0, rect.bottom - rect.top - iconHeight, hIcon, iconWidth, iconHeight, NULL, NULL, DI_NORMAL);
-          offx += iconWidth;
-        }
-#ifdef _DEBUG
-        // Display version
-        HFONT hFont = (HFONT)::SendMessage(pClass->m_hStatusBarWnd, WM_GETFONT, 0, 0);
-        HGDIOBJ hOldFont = ::SelectObject(hDC,hFont);
-
-        AdblockPlus::Rectangle rcText = rcClient;
-        rcText.left += offx;
-        ::SetBkMode(hDC, TRANSPARENT);
-        ::DrawTextW(hDC, IEPLUGIN_VERSION, -1, &rcText, DT_WORD_ELLIPSIS|DT_LEFT|DT_SINGLELINE|DT_VCENTER);
-
-        ::SelectObject(hDC, hOldFont);
-#endif // _DEBUG
-      }
-
-      // Done!
-      EndPaint(hWnd, &ps);
-
-      return 0;
-    }
-
-  case WM_LBUTTONUP:
-  case WM_RBUTTONUP:
-    {
-      std::wstring url = pClass->GetBrowserUrl();
-      if (url != pClass->GetTab()->GetDocumentUrl())
-      {
-        pClass->GetTab()->SetDocumentUrl(url);
-      }
-
-      // Create menu
-      HMENU hMenu = pClass->CreatePluginMenu(url);
-      if (!hMenu)
-      {
-        return 0;
-      }
-
-      // Display menu
-      POINT pt;
-      ::GetCursorPos(&pt);
-
-      RECT rc;
-      ::GetWindowRect(hWnd, &rc);
-
-      if (rc.left >= 0 && rc.top >= 0)
-      {
-        pt.x = rc.left;
-        pt.y = rc.top;
-      }
-
-      pClass->DisplayPluginMenu(hMenu, -1, pt, TPM_LEFTALIGN|TPM_BOTTOMALIGN);
-    }
-    break;
-  case WM_DESTROY:
-    break;
-  case SC_CLOSE:
-    break;
-
-  case WM_UPDATEUISTATE:
-    {
-      CPluginTab* tab = GetTab(::GetCurrentThreadId());
-      if (tab)
-      {
-        tab->OnActivate();
+          GetWindowRect(pClass->m_hPaneWnd, &rect);
+          pClass->notificationMessage.MoveToCenter(rect);
+        }
+        if (LOWORD(wParam) == UIS_CLEAR)
+        {
+          pClass->notificationMessage.Hide();
+        }
+        break;
+      }
+    case WM_WINDOWPOSCHANGING:
+      {
         RECT rect;
         GetWindowRect(pClass->m_hPaneWnd, &rect);
-        pClass->notificationMessage.Move(rect.left + (rect.right - rect.left) / 2, rect.top + (rect.bottom - rect.top) / 2); 
-      }
-      if (LOWORD(wParam) == UIS_CLEAR)
-      {
-        pClass->notificationMessage.Hide();
-      }
-    }
-    break;
-  case WM_WINDOWPOSCHANGING:
-    {
-      RECT rect;
-      GetWindowRect(pClass->m_hPaneWnd, &rect);
-      if (pClass->notificationMessage.IsVisible())
-      {
-        pClass->notificationMessage.Move(rect.left + (rect.right - rect.left) / 2, rect.top + (rect.bottom - rect.top) / 2); 
-      }
-    }
-    break;
-  case WM_WINDOWPOSCHANGED:
-    {
-      WINDOWPOS* wndPos = reinterpret_cast<WINDOWPOS*>(lParam);
-      if (wndPos->flags & SWP_HIDEWINDOW)
-      {
-        pClass->notificationMessage.Hide();
-      }
-    }
-    break;
-  case WM_ALREADY_UP_TO_DATE:
-    {
-      Dictionary* dictionary = Dictionary::GetInstance();
-      std::wstring upToDateText = dictionary->Lookup("updater", "update-already-up-to-date-text");
-      std::wstring upToDateTitle = dictionary->Lookup("updater", "update-already-up-to-date-title");
-      pClass->notificationMessage.SetTextAndIcon(upToDateText, upToDateTitle, TTI_INFO);
-    }
-    break;
-  case WM_UPDATE_CHECK_ERROR:
-    {
-      Dictionary* dictionary = Dictionary::GetInstance();
-      std::wstring errorText = dictionary->Lookup("updater", "update-error-text");
-      std::wstring errorTitle = dictionary->Lookup("updater", "update-error-title");
-      pClass->notificationMessage.SetTextAndIcon(errorText, errorText, TTI_ERROR);
-    }
-    break;
-  case WM_DOWNLOADING_UPDATE:
-    {
-      Dictionary* dictionary = Dictionary::GetInstance();
-      std::wstring downloadingText = dictionary->Lookup("updater", "downloading-update-text");
-      std::wstring downloadingTitle = dictionary->Lookup("updater", "downloading-update-title");
-      pClass->notificationMessage.SetTextAndIcon(downloadingText, downloadingTitle, TTI_INFO);
-    }
-    break;
-  }
-
-  return DefWindowProc(hWnd, message, wParam, lParam);
+        if (pClass->notificationMessage.IsVisible())
+        {
+          pClass->notificationMessage.MoveToCenter(rect);
+        }
+        break;
+      }
+    case WM_WINDOWPOSCHANGED:
+      {
+        WINDOWPOS* wndPos = reinterpret_cast<WINDOWPOS*>(lParam);
+        if (wndPos->flags & SWP_HIDEWINDOW)
+        {
+          pClass->notificationMessage.Hide();
+        }
+        break;
+      }
+    case WM_ALREADY_UP_TO_DATE:
+      {
+        Dictionary* dictionary = Dictionary::GetInstance();
+        std::wstring upToDateText = dictionary->Lookup("updater", "update-already-up-to-date-text");
+        std::wstring upToDateTitle = dictionary->Lookup("updater", "update-already-up-to-date-title");
+        pClass->notificationMessage.SetTextAndIcon(upToDateText, upToDateTitle, TTI_INFO);
+        break;
+      }
+    case WM_UPDATE_CHECK_ERROR:
+      {
+        Dictionary* dictionary = Dictionary::GetInstance();
+        std::wstring errorText = dictionary->Lookup("updater", "update-error-text");
+        std::wstring errorTitle = dictionary->Lookup("updater", "update-error-title");
+        pClass->notificationMessage.SetTextAndIcon(errorText, errorTitle, TTI_ERROR);
+        break;
+      }
+    case WM_DOWNLOADING_UPDATE:
+      {
+        Dictionary* dictionary = Dictionary::GetInstance();
+        std::wstring downloadingText = dictionary->Lookup("updater", "downloading-update-text");
+        std::wstring downloadingTitle = dictionary->Lookup("updater", "downloading-update-title");
+        pClass->notificationMessage.SetTextAndIcon(downloadingText, downloadingTitle, TTI_INFO);
+        break;
+      }
+    }
+  }
+  catch (...)
+  {
+    // Suppress exception. Fall through to default handler.
+    DEBUG_GENERAL(L"CPluginClass::PaneWindowProc - exception");
+  }
+  return ::DefWindowProc(hWnd, message, wParam, lParam);
 }
 
 
 void CPluginClass::UpdateStatusBar()
 {
   DEBUG_GENERAL("*** Updating statusbar")
   if (m_hPaneWnd == NULL)
   {
     CreateStatusBarPane();
   }
@@ skipping 48 matching lines @@
   s_criticalSectionLocal.Unlock();
 
   return icon;
 }
 
 ATOM CPluginClass::GetAtomPaneClass()
 {
   return s_atomPaneClass;
 }