CODEWITHSUNDEEP
c#winapiwaitforsingleobject
Jack
Jack

Reputation: 16724

WaitForSingleObject return ERROR_INVALID_HANDLE

I'm trying to determine if a process is still alive (at the moment I did check, I'm aware it can be closed right after I do the check) by calling WaitForSingleObject() with a handle get from Process.MainWindowHandle which works just fine with IsIconic() but it return WAIT_FAILED and GetLastError() a ERROR_INVALID_HANDLE

UInt32 r = WaitForSingleObject(handle, 0);
if(r == WAIT_OBJECT_0)
{
    MessageBox.Show("still running!");
}
if(r == WAIT_FAILED)
{
    throw new Win32Exception(Marshal.GetLastWin32Error());
}

Upvotes: 2

Views: 1645

Answers (1)

Cody Gray
Cody Gray

Reputation: 244672

You cannot wait on a window handle. You can pass window handles to window-related functions, like IsIconic(), but they are not kernel objects so you cannot wait on them. The documentation gives a list of objects that you can wait on:

The WaitForSingleObject function can wait for the following objects:

  • Change notification
  • Console input
  • Event
  • Memory resource notification
  • Mutex
  • Process
  • Semaphore
  • Thread
  • Waitable timer

So, if you want to wait on a process until it ends, you can wait on the process's handle, which is accessible via the Process.Handle property.

But you don't actually need to P/Invoke the Win32 function at all. The .NET Process wrapper class has WaitForExit() and WaitForInputIdle() member functions that can be used to wait on a process (note that both have overloads taking a timeout value).

If this is a process that you started using the Process class wrapper, you can simply interrogate the Process.HasExited property.

Upvotes: 5

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