How to use OpenProcessToken, AdjustTokenPrivileges, and GetExitCodeProcess in VC++ 2005

Question

I read a couple of posts on how to check if a process has exited from a different process (I realize some people get hung up on semantics here, but just humor me) and I tried to implement it but am running into the error code 5 ("ERROR_ACCESS_DENIED") all over the place.

Here is what I do.

1) Process 1 (P1) launches process 2 and writes to a shared memory location its own PID.

2) Process 2 (P2) reads the PID from shared memory

3) P2 calls OpenProcess(...) with P1's PID to save a handle that it can check later.

4) P2 calls GetExitCodeProcess(...) with P1's PID repeatedly and checks for a STILL_ACTIVE code.

In the above method, I keep getting the ACCESS_DENIED error on GetExitCodeProcess. I've tried modifying P2's privileges by using the below code from MSDN's docs:

HANDLE proc_h = OpenProcess(SYNCHRONIZE, FALSE, GetCurrentProcessId());
HANDLE hToken;
OpenProcessToken(proc_h, TOKEN_ADJUST_PRIVILEGES, &hToken);

LookupPrivilegeValue(NULL, lpszPrivilege, &luid );

tp.PrivilegeCount = 1;
tp.Privileges[0].Luid = luid;
tp.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;
// Enable the privilege
AdjustTokenPrivileges(hToken, 
                      FALSE, 
                      &tp, 
                      sizeof(TOKEN_PRIVILEGES), 
                      (PTOKEN_PRIVILEGES) NULL, 
                      (PDWORD) NULL);

But I keep getting the ACCESS_DENIED error on the call to OpenProcessToken(...) method. So does this indicate some sort of system level hurdle? I do have admin rights on my machine and I'm running XP.

Thanks in advance for any help.

Answer 1

The handle passed to GetExitCodeProcess requires PROCESS_QUERY_INFORMATION access right. The following works fine:

int main(int a_argc, char** a_argv)
{
    int pid = atoi(*(a_argv + 1));

    HANDLE h = OpenProcess(PROCESS_QUERY_INFORMATION, FALSE, pid);

    if (NULL != h)
    {
        Sleep(2000);
        DWORD exit_code;
        if (FALSE == GetExitCodeProcess(h, &exit_code))
        {
            std::cerr << "GetExitCodeProcess() failure: " <<
                GetLastError() << "\n";
        }
        else if (STILL_ACTIVE == exit_code)
        {
            std::cout << "Still running\n";
        }
        else
        {
            std::cout << "exit code=" << exit_code << "\n";
        }
    }
    else
    {
        std::cerr << "OpenProcess() failure: " << GetLastError() << "\n";
    }

    return 0;
}

Instead of polling on GetExitCodeProcess open the handle with SYNCHRONIZE and wait for it to exit:

int main(int a_argc, char** a_argv)
{
    int pid = atoi(*(a_argv + 1));

    HANDLE h = OpenProcess(SYNCHRONIZE | PROCESS_QUERY_INFORMATION, FALSE, pid);

    if (NULL != h)
    {
        WaitForSingleObject(h, 5000); // Change to 'INFINITE' wait if req'd
        DWORD exit_code;
        if (FALSE == GetExitCodeProcess(h, &exit_code))
        {
            std::cerr << "GetExitCodeProcess() failure: " <<
                GetLastError() << "\n";
        }
        else if (STILL_ACTIVE == exit_code)
        {
            std::cout << "Still running\n";
        }
        else
        {
            std::cout << "exit code=" << exit_code << "\n";
        }
    }
    else
    {
        std::cerr << "OpenProcess() failure: " << GetLastError() << "\n";
    }

    return 0;
}

Answer 2

OpenProcesstoken requires PROCESS_QUERY_INFORMATION you are opening the process with only SYNCHRONIZE access. See if you add | PROCESS_QUERY_INFORMATION if it works.

Answer 3

If you just want P2 to do something when P1 exits, there's another way that's probably rather easier: have P1 create a pipe and let P2 inherit a handle to that pipe. In P2, execute a read from the pipe. When P2's call to ReadFile returns with an error of ERROR_BROKEN_PIPE, P1 has exited.