Asynchronous input notification from Windows console

Question

I need to get user input from console asynchronously, i.e. without blocking. I could use the following Python code to check if there is an input available, but it gives 100% CPU load.

import msvcrt
while not msvcrt.kbhit():
    pass

Is there any other way to do this? Is it possible to register a callback function for keyboard events in console, for example?

UPDATE: I've created a working solution in Python / ctypes. See example at http://techtonik.rainforce.org/2011/03/asynchronous-input-from-windows-console.html

Ben Voigt · Accepted Answer · 2011-03-25 21:21:57Z

2

Using the Win32 API, you would normally call WaitForMultipleObjects along with your other events to find out which occurred first, the standard input handle itself will be considered triggered whenever any input is available.

A process can specify a console input buffer handle in one of the wait functions to determine when there is unread console input. When the input buffer is not empty, the state of a console input buffer handle is signaled.

So I would suggest that you look and see whether python has some wrapper for this ability.

edited Mar 25, 2011 at 21:21

answered Mar 25, 2011 at 19:35

Ben Voigt

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3 Comments

anatoly techtonik Over a year ago

Seems helpful. I can try it with ctypes, but does WaitForMultipleObjects work with ordinary console? It will help a lot to have working example in a different language before trying to do the same with ctypes.

Ben Voigt Over a year ago

@techtonik: This example looks like it might help. And here's one from Microsoft.

anatoly techtonik Over a year ago

Thanks. Even though there are problems with clearing the buffer, at least WaitForMultipleObjects seems to work.

tamarintech · Accepted Answer · 2011-03-25 19:30:18Z

0

There isn't a way to asynchronously get console input/output.

You could try your code with a sleep to prevent the CPU usage spike.

answered Mar 25, 2011 at 19:30

tamarintech

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1 Comment

anatoly techtonik Over a year ago

That's the most obvious suggestion, but I don't want to miss CPU cycles if a need in heavy background processing arises.

ikegami · Accepted Answer · 2011-03-25 19:34:39Z

0

msvcrt.getch()

answered Mar 25, 2011 at 19:34

ikegami

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3 Comments

Ben Voigt Over a year ago

That's still a blocking function.

ikegami Over a year ago

well yeah. You either use a blocking function, or you poll using up CPU.

Ben Voigt Over a year ago

Plenty of other options in native Win32, it just remains to be seen whether python lets you get there from here. Yes, to some degree all event-driven programming requires some blocking function, the trick is to use a blocking function that processes all types of events, not dedicated to a single one.

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