How do I automatically destroy child processes in Windows?

Question

In C++ Windows app, I launch several long running child processes (currently I use CreateProcess(...) to do this.

I want the child processes to be automatically closed if my main processes crashes or is closed.

Because of the requirement that this needs to work for a crash of the "parent", I believe this would need to be done using some API/feature of the operating system. So that all the "child" processes are cleaned up.

How do I do this?

Answer 1

The Windows API supports objects called "Job Objects". The following code will create a "job" that is configured to shut down all processes when the main application ends (when its handles are cleaned up). This code should only be run once.:

HANDLE ghJob = CreateJobObject( NULL, NULL); // GLOBAL if( ghJob == NULL) {     ::MessageBox( 0, "Could not create job object", "TEST", MB_OK); } else {     JOBOBJECT_EXTENDED_LIMIT_INFORMATION jeli = { 0 };      // Configure all child processes associated with the job to terminate when the     jeli.BasicLimitInformation.LimitFlags = JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE;     if( 0 == SetInformationJobObject( ghJob, JobObjectExtendedLimitInformation, &jeli, sizeof(jeli)))     {         ::MessageBox( 0, "Could not SetInformationJobObject", "TEST", MB_OK);     } } 

Then when each child process is created, execute the following code to launch each child each process and add it to the job object:

STARTUPINFO info={sizeof(info)}; PROCESS_INFORMATION processInfo;  // Launch child process - example is notepad.exe if (::CreateProcess( NULL, "notepad.exe", NULL, NULL, TRUE, 0, NULL, NULL, &info, &processInfo)) {     ::MessageBox( 0, "CreateProcess succeeded.", "TEST", MB_OK);     if(ghJob)     {         if(0 == AssignProcessToJobObject( ghJob, processInfo.hProcess))         {             ::MessageBox( 0, "Could not AssignProcessToObject", "TEST", MB_OK);         }     }      // Can we free handles now? Not sure about this.     //CloseHandle(processInfo.hProcess);      CloseHandle(processInfo.hThread); } 

VISTA NOTE: See AssignProcessToJobObject always return "access denied" on Vista if you encounter access-denied issues with AssignProcessToObject() on vista.

Answer 2

One somewhat hackish solution would be for the parent process to attach to each child as a debugger (use DebugActiveProcess). When a debugger terminates all its debuggee processes are terminated as well.

A better solution (assuming you wrote the child processes as well) would be to have the child processes monitor the parent and exit if it goes away.