Use a named mutex to avoid race conditions

src/engine/main.cpp

 #include <AdblockPlus.h>
 #include <vector>
 #include <Windows.h>
 
 #include "../shared/AutoHandle.h"
 #include "../shared/Communication.h"
 #include "../shared/Utils.h"
 #include "../shared/Version.h"
 #include "Debug.h"
 
@@ skipping 169 matching lines @@
 
   AdblockPlus::JsEnginePtr jsEngine = AdblockPlus::JsEngine::New(appInfo);
   std::string dataPath = ToUtf8String(GetAppDataPath());
   dynamic_cast<AdblockPlus::DefaultFileSystem*>(jsEngine->GetFileSystem().get())->SetBasePath(dataPath);
   std::auto_ptr<AdblockPlus::FilterEngine> filterEngine(new AdblockPlus::FilterEngine(jsEngine));
   return filterEngine;
 }
 
 int WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int)
 {
-  if (Communication::PipeExists(Communication::pipeName))
+  AutoHandle mutex(CreateMutexW(0, false, L"AdblockPlusEngine"));

[Oleksandr, 2013/06/07 14:52:09]

Shouldn't this be Global\AdblockPlusEngine?

+  if (!mutex)
+  {
+    DebugLastError("CreateMutex failed");
+    return 1;
+  }
+
+  if (GetLastError() == ERROR_ALREADY_EXISTS)
   {
     DebugLastError("Named pipe exists, another engine instance appears to be running");
     return 1;
   }

[Wladimir Palant, 2013/06/07 14:32:01]

Remove the block of code above?

[Felix Dahlke, 2013/06/07 14:33:25]

What in particular? The check for ERROR_ALREADY_EXISTS? That's necessary.
CreateMutex will open an already existing mutex, but set last error to that.
That's how we can figure out if there was one already.

[Wladimir Palant, 2013/06/07 14:46:45]

Ok, that debug message is misleading then. How about:

if (!mutex || GetLastError() == ERROR_ALREADY_EXISTS)
{
  DebugLastError("Failed to create a mutex, another engine instance appears to
be running");
  return 1;
}

 
   int argc;
   LPWSTR* argv = CommandLineToArgvW(GetCommandLineW(), &argc);
   std::wstring locale(argc >= 1 ? argv[0] : L"");
   LocalFree(argv);
 
   filterEngine = CreateFilterEngine(locale);
 
   for (;;)
   {
@@ skipping 13 matching lines @@
     }
     catch (std::runtime_error e)
     {
       DebugException(e);
       return 1;
     }
   }
 
   return 0;
 }