Get Parent Process PID

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Introduction

Sometimes, you might be in a situation when your application is launched by another program, which cannot be modified to change its behavior.

If you can not grab any COM interface or a meaningful Windows handle, then the only thing left is the process handle to deal with. One thing you can do with such a handle is to try to do some interprocess synchronization.

There are two programs included in the workspace, a startup MFC application that will merely launch the child, and the child application called GetParentProcID.exe that will latch onto its parent and wait for its termination.

Background

Unfortunately, Win32 does not have an API that gives you the PID of the parent process, and you have to create it yourself. We will use functions found in Psapi.dll and in the Kernel32.DLL, that will be loaded programmatically.

Using the code

In short, we need to iterate through the processes running on the machine, identify the current process entry, and use it to retrieve the parent’s PID.

We begin by getting the handle to a Toolhelp snapshot of the systems.

hSnapShot = lpfCreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0 );

This handle is used to iterate through the process entries and compare them against the current process ID:

     bContinue = lpfProcess32First( hSnapShot, &procentry ) ;
     DWORD pid = 0;
         // While there are processes, keep looping.

     DWORD  crtpid= GetCurrentProcessId();
         while( bContinue )
         {
        if(crtpid == procentry.th32ProcessID)
            pid =  procentry.th32ParentProcessID;

               procentry.dwSize = sizeof(PROCESSENTRY32) ;
               bContinue = !pid && lpfProcess32Next( hSnapShot, &procentry );
         }//while ends

The PROCESSENTRY32 structure we got from our GetParentProcID function is passed down to the WaitForParentToFinish, that does the synchronization:

The parent process PID is the th32ParentProcessID data member of this structure.

There are two things to note about this last function:

1. We need to get a process handle that can be used for synchronization (hence the SYNCHRONIZE flag):

   HANDLE hProcess = OpenProcess(
                  SYNCHRONIZE | PROCESS_QUERY_INFORMATION | PROCESS_VM_READ,
                  FALSE, procentry.th32ParentProcessID ) ;

2. The parent’s file name can be retrieved using EnumProcessModules and grabbing the name from the first module by calling GetModuleFileNameEx:

   if( EnumProcessModules( hProcess, &hMod, sizeof( hMod ), &dwSize2 ) )
   {
       if( !GetModuleFileNameEx( hProcess, hMod,
                   szFileName, sizeof( szFileName ) ) )
       {.......

Once we have all the info about the parent, we can wait for its termination by calling WaitForSingleObject:

    while(dwres = WaitForSingleObject(hProcess,
                TIMEOUT) == WAIT_TIMEOUT)//wait up to TIMEOUT ms

    {
        printf("TimedOut waiting for %s after %d ms\n", pszName,TIMEOUT);
    }
    printf((WAIT_OBJECT_0 == dwres)?
      "waiting for parent termination SUCCEEDED\n" :
      "parent waiting FAILED\n");