Run a function at every iteration of a GLib.MainLoop

Question

I'm writing a simple Python 3 program that uses PyDBus and GLib.

I'm trying to use PyDBus to send a signal whenever an edge event is detected on a Raspberry Pi GPIO pin.

To do that, the function that does this task needs to be called at every iteration of the main loop. I've seen that the timeout_add function does a similar action; however, timeout_add runs my function only every interval milliseconds.

Is there a way to call it at every iteration instead?

Answer 1

Use g_idle_add(). It creates a GSource with no preconditions, and a low priority, so its callback function is executed once per main context iteration, at a lower priority than other pending events.

If you need to bump the priority, use g_idle_add_full() similarly.

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As @nemequ says above, though, the architecturally best solution is to write your own GSource implementation (see the documentation for GSourceFuncs), which could behave the same as a source created with g_idle_add(), or could improve performance from knowing the specifics of the I/O pin you’re querying. It all depends on the API the kernel exposes for that I/O pin, and how that’s pollable from user space.

There is documentation on writing a custom GSource here.