Hacktoberfest 2026: the issues maintainers tagged for October, open and beginner-friendly. Browse Hacktoberfest issues

All registered callbacks are removed once UnregisterCallbackForPinValueChangedEvent is called

Open
  • Is something wrong?
#2,619 0 comments 0 reactions 0 assignees View on GitHub

Maintainers usually reply within 1 day

Nobody has claimed this yet.

Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
30/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
csharp, linux, raspberry-pi
Domain
embedded-iot

Research direction

Start in the Raspberry Pi 3 Linux driver's RemoveCallbackForPinValueChangedEvent, where ClosePin is now called unconditionally, then compare it with LibGpiodV2Driver.ClosePin and the _eventObserver.HasSubscriptionsFor check that keeps the line open. Done when removing one of two callbacks on the same pin keeps the other receiving events and a second unregister no longer throws. The fix needs a real Raspberry Pi or a hardware-in-the-loop test to confirm.

Written by the indexing model from the issue text.

Description

untriaged

I tested this PR on a Raspberry Pi 3 B+ with libgpiod v2 (Debian 13, libgpiod 2.2.1), and it also fixes #2614: a second RegisterCallbackForPinValueChangedEvent, UnregisterCallbackForPinValueChangedEvent and WaitForEvent no longer throw Device or resource busy. Registering, unregistering and registering a callback again works, and so does WaitForEvent (twice in a row, and before registering a callback).

One case still fails: two callbacks on the same pin. After one of them is unregistered, the other one gets no more events, and unregistering it throws InvalidOperationException: Pin 8 is not in use for callbacks.

controller.OpenPin(Pin, PinMode.Input);
controller.RegisterCallbackForPinValueChangedEvent(Pin, PinEventTypes.Rising | PinEventTypes.Falling, OnChange);
controller.RegisterCallbackForPinValueChangedEvent(Pin, PinEventTypes.Rising, OnChange2);
controller.UnregisterCallbackForPinValueChangedEvent(Pin, OnChange2); // OnChange gets no more events
controller.UnregisterCallbackForPinValueChangedEvent(Pin, OnChange);  // InvalidOperationException

GPIO 8 had nothing connected, and the edges came from switching its internal pull-up and pull-down with pinctrl set 8 pu / pd (4 edges after each step):

After OnChange (rising and falling) OnChange2 (rising)
Registering OnChange 4 of 4 —
Registering OnChange2 4 of 4 2 of 2
Unregistering OnChange2 0 of 4 —

The cause seems to be that RaspberryPi3LinuxDriver.RemoveCallbackForPinValueChangedEvent now always calls _interruptDriver.ClosePin(pinNumber) and sets InUseByInterruptDriver = false. LibGpiodV2Driver.ClosePin disposes the line request and removes all the subscriptions of the line, although LibGpiodV2Driver.RemoveCallbackForPinValueChangedEvent already keeps the line while other callbacks remain (_eventObserver.HasSubscriptionsFor(offset)). Maybe the pin should be closed in the interrupt driver only when its last callback is removed.

Tested at a2740357, built on Windows with .NET SDK 10.0.401 (linux-arm64). With System.Device.Gpio 4.2.0, the same program fails as described in #2614.

Originally posted by @Kash0321 in https://github.com/dotnet/iot/issues/2610#issuecomment-5973268665

Dominant language
C#
Stars
2.4k
Forks
630
Avg merge
6d 19h
Merged PRs (30d)
11

Getting set up

  • No Dockerfile or Docker Compose file
  • Has a pull request template
  • No contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from dotnet/iot

All issues in dotnet/iot

Similar issues

More C# issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.