Question

I need to catch process termination signals for child processes.

So for example, if my Win32 console application spawns a notepad process and the user closes notepad, I would like to detect that.

I don’t want to block (asynchronous model)

I’m creating a process using the win api CreateProcess

Answer 1

Have you tried WaitForSingleObject() with it’s dwMilliseconds parameter as 0? WaitForSingleObject() will return immediately if dwMilliseconds is 0 and will return WAIT_TIMEOUT if the process isn’t dead or WAIT_OBJECT_0 if it is.
Example, assuming the child process handle is hProcess:

DWORD result = WaitForSingleObject(hProcess, 0);
if (result == WAIT_TIMEOUT)
    /* Process not dead */;
else if (result == WAIT_OBJECT_0)
    /* Process dead */;
else
    /* Error occured */;

And alternative is GetExitCodeProcess(). The “exit code” returned by it will be STILL_ACTIVE if it is still running, otherwise it will return the actual exit code.
Example, again assuming the child process handle is hProcess:

DWORD exitCode;
if (!GetExitCodeProcess(hProcess, &exitCode))
    /* Error occured */;
else if (exitCode == STILL_ACTIVE)
    /* Process is still running */
else
    /* exitCode now contains the process exit code, and the process is not running anymore */;

Both these examples are non-blocking