Thanks, I am not sure how this helps with the next steps that you are envisioning and thus cannot formulate an opinion on these changes. For me to understand a little better: Would the existing "Thread" class still exist after these changes or simplify?

With the new update just now the controller and threading is further disentangled by registering the callbacks of the controller in the thread class. Now the controller only supports the threading-functions as follows:

• SignalValidSetup()
• SignalInValidSetup()
• CheckValidSetup()
• IsStopped()
• BlockIfPaused()

Note that now functions such as Start(), IsStarted(), Wait(), etc. is not supported in the controller anymore, and can only be called in the ControllerThread class.

Also, @sarlinpe suggested to combine BlockIfPaused() and IsStopped() together in a CheckIfStopped() method, such that we can modify this handle in python in the future outside the C++ threading design. I have made this possible and integrated into the IncrementalMapperController, such that now in the IncrementalMapperController we only used this CheckIfStopped method.

@ahojnnes About the next steps, Now the new design is only integrated in the IncrementalMapperController as a draft. The initial plan is indeed to replace the Thread class with ControllerThread in the end. But I also have no problem to keep the Thread class implementation for convenience (while it may cause confusion in the future). In the end BaseController will go into the controller folder, and ControllerThread can stay in the ui or be put into the threading header. If approved we can update all the controller with this new design and then we can split the Run() method further into substeps, such that we can support better and detailed bindings in Python.

The polymorphism with active_thread_ in the mapper controller can be further supported with the SetCheckIfStoppedFunc method from the controller (f82b002#diff-faf29b81ac33239a3b5179ec793d7f032660ae99f8cf1865341f7b4eb09476edR230), which is a callback that returns boolean value. This is also used in the IncrementalMapperController.

@B1ueber2y This design is much cleaner than the previous one. I think that we can move more threading logic out of the BaseController - see my comments.

I have made a new design update on the ControllerThread class by directly inheriting from Thread. The only added feature is

• AddControllerCallback which adds controller-specific callbacks (e.g., https://github.com/colmap/colmap/pull/2392/files#diff-517534814bb88b451c2f5f4856136755190c58987f0870fa50939d2115124704R626)
• combine BlockIfPaused() and IsStopped() into a CheckIfStopped() function in the controller

In this design we wont deprecate the Thread class, but can still migrate most controller class into the new design to disentangle the threading. This feels like a far more elegant way to me and also the update becomes more stable without significant changes.

LGTM, great work, thanks a lot!

Thanks, looks great. I assume you will follow up with equivalent changes for other controllers?