Benefits of the Proposed Modification

Oct 13, 2025 by wbrum.org 45 views

Introduction

In the context of Pandablocks FastCS, setting multiple AttrRW attributes to the same value can be a common requirement. However, adding a callback to handle this scenario can lead to recursive callback triggering, which can be problematic. To address this issue, we propose a modification to the _update_callbacks method, renaming it to _transport_update_callbacks and _user_update_callbacks. This change will enable the transport update callbacks to run always, while introducing a new keyword argument run_update_callbacks for AttrR.set, which can be used to toggle the execution of user update callbacks.

Current Implementation

The current implementation of the _update_callbacks method in the handlers.py file of the FastCS Pandablocks repository is as follows:

def _update_callbacks(self, attr, value):
    # ...
    if attr not in self._value_cache:
        # ...
        self._value_cache[attr] = value
        # ...
    # ...

As shown in the code snippet above, the _update_callbacks method checks if the attribute value is already set in the _value_cache dictionary before updating it. This is done to prevent recursive callback triggering.

Proposed Modification

To address the issue of recursive callback triggering, we propose the following modification to the _update_callbacks method:

def _transport_update_callbacks(self, attr, value):
    # ...
    self._value_cache[attr] = value
    # ...

def _user_update_callbacks(self, attr, value):
    # ...
    if attr not in self._value_cache:
        # ...
        self._value_cache[attr] = value
        # ...
    # ...

In this modified implementation, we introduce two separate methods: _transport_update_callbacks and _user_update_callbacks. The _transport_update_callbacks method will always run, updating the attribute value in the _value_cache dictionary. The _user_update_callbacks method will only run if the run_update_callbacks keyword argument is set to True when calling AttrR.set.

Allowing Setting `AttrR`/`AttrRW` without Running Callbacks

To enable setting AttrR/AttrRW attributes without running the callbacks added downstream, we propose the following changes to the AttrR class:

class AttrR:
    def set(self, value, run_update_callbacks=True):
        # ...
        if run_update_callbacks:
            self._user_update_callbacks(self, value)
        # ...

In this modified implementation, the set method of the AttrR class takes an additional keyword argument run_update_callbacks, which defaults to True. If run_update_callbacks is set to False, the _user_update_callbacks method will not be called, allowing the attribute value to be set without running the callbacks added downstream.

Benefits of the Proposed Modification

The proposed modification to the _update_callbacks method and the introduction of the run_update_callbacks keyword argument in the AttrR class offer several benefits:

Improved performance: By allowing the attribute value to be set without running the callbacks added downstream, the proposed modification can improve performance by reducing the number of callback executions.
Reduced complexity: The proposed modification simplifies the implementation of the _update_callbacks method by separating the transport update callbacks from the user update callbacks.
Increased flexibility: The introduction of the run_update_callbacks keyword argument provides developers with more flexibility when setting AttrR/AttrRW attributes, allowing them to choose whether to run the callbacks added downstream.

Conclusion

Q&A

Q: What is the current implementation of the _update_callbacks method in the handlers.py file of the FastCS Pandablocks repository?

A: The current implementation of the _update_callbacks method in the handlers.py file of the FastCS Pandablocks repository is as follows:

def _update_callbacks(self, attr, value):
    # ...
    if attr not in self._value_cache:
        # ...
        self._value_cache[attr] = value
        # ...
    # ...

Q: Why is the _update_callbacks method checking if the attribute value is already set in the _value_cache dictionary before updating it?

A: The _update_callbacks method checks if the attribute value is already set in the _value_cache dictionary before updating it to prevent recursive callback triggering.

Q: What is the proposed modification to the _update_callbacks method?

A: The proposed modification to the _update_callbacks method is to rename it to _transport_update_callbacks and _user_update_callbacks. The transport update callbacks will always be ran, however AttrR.set will have a kwarg for run_update_callbacks=True which can toggle whether _user_update_callbacks will be ran.

Q: How will the proposed modification improve performance?

A: The proposed modification will improve performance by reducing the number of callback executions. By allowing the attribute value to be set without running the callbacks added downstream, the proposed modification can reduce the overhead of callback execution.

Q: How will the proposed modification simplify the implementation of the _update_callbacks method?

A: The proposed modification will simplify the implementation of the _update_callbacks method by separating the transport update callbacks from the user update callbacks. This will make the code easier to understand and maintain.

Q: How will the introduction of the run_update_callbacks keyword argument provide developers with more flexibility?

A: The introduction of the run_update_callbacks keyword argument will provide developers with more flexibility when setting AttrR/AttrRW attributes. They will be able to choose whether to run the callbacks added downstream, depending on their specific use case.

Q: What are the benefits of the proposed modification?

A: The benefits of the proposed modification include:

Improved performance: By reducing the number of callback executions, the proposed modification can improve performance.
Reduced complexity: The proposed modification simplifies the implementation of the _update_callbacks method by separating the transport update callbacks from the user update callbacks.
Increased flexibility: The introduction of the run_update_callbacks keyword argument provides developers with more flexibility when setting AttrR/AttrRW attributes.

Q: How can developers take advantage of the proposed modification?

A: Developers can take advantage of the proposed modification by using the run_update_callbacks keyword argument when setting AttrR/AttrRW attributes. They can choose whether to run the callbacks added downstream, depending on their specific use case.

Q: What are the potential use cases for the proposed modification?

A: The potential use cases for the proposed modification include:

Setting multiple AttrRW attributes to the same value: The proposed modification can be used to set multiple AttrRW attributes to the same value without running the callbacks added downstream.
Improving performance: The proposed modification can be used to improve performance by reducing the number of callback executions.
Simplifying code: The proposed modification can be used to simplify code by separating the transport update callbacks from the user update callbacks.

Conclusion

In conclusion, the proposed modification to the _update_callbacks method and the introduction of the run_update_callbacks keyword argument in the AttrR class offer several benefits, including improved performance, reduced complexity, and increased flexibility. By allowing setting AttrR/AttrRW attributes without running the callbacks added downstream, developers can write more efficient and effective code.