I have a Dash application that queries an API, based on a user search query, performs some calculations on the response, then displays the final results to the user on a Dash app. In order to provide a quick response to the user, I am trying to set up a quick result callback and a full result long_callback.
The quick result will grab limited results from the API and display results to the user within 10-15 seconds, while the full results will run in the background, collecting all results (which can take up to 2 minutes), then updates the page with the full results when they are available.
I am curious what the best way to perform this action is, as I have run into forking issues with my current attempt.
My current attempt: Using the diskcache.Cache() as the DiskcacheLongCallbackManager and a database txt file to store availability of results.
- I have a database txt file that stores a dictionary, with the keys being the search query and the fields being quick_results: bool, full_results: bool, file_path: str, timestamp: dt (as str).
- When a search query is entered and submit is pressed, a callback loads the database file as a variable and then checks the dictionary keys for the presence of this search query.
- If it finds the query in the keys of the database, it loads the saved feather file from the provided file_path and returns it to the dash app for generation of the page content.
- If it does not find the query in the database keys, it requests limited data from the API, runs calculations, saves the DataFrame as a feather file on disk, then creates an entry in the database with the search query(as the key), the file path of the saved feather file, the current timestamp, and sets the quick_results value to True.
- It then loads this feather file from the file_path created and returns it to the dash app for generation of the page content.
- A long_callback is triggered at the same time as the above callback, with a 20 second sleep to prevent overlap with the quick search. This callback also loads the database file as a variable and checks if the query is present in the database keys.
- If found, it then checks if the full results value is True and if the timestamp is more than 0 days old.
- If the full results are unavailable or are more than 0 days old, the long_callback requests full results from the API, performs the same calculations, then updates the already existing search query in the database, making the full_results True and the timestamp the time of completion for the full search.
- It then loads the feather file from the file_path and returns it to the dash app for generation of the page content.
- If the results are available and less then 1 day old, the long callback simply loads the feather file from the provided file_path and returns it to the dash app for generation of the page content.
The problem I am currently facing is that I am getting a weird forking error on the long callback on only one of the conditions for a full search. I currently have the long_callback setup to perform a full search only if the full results flag is False or the results are more than 0 days old. When the full_results flag is False, the callback runs as expected, updates the database and returns the full results. However, when the results are available but more than 0 days old, the callback hits a forking error and is unable to complete.
The process has forked and you cannot use this CoreFoundation functionality safely. You MUST exec(). Break on __THE_PROCESS_HAS_FORKED_AND_YOU_CANNOT_USE_THIS_COREFOUNDATION_FUNCTIONALITY___YOU_MUST_EXEC__() to debug.
I am at a loss as to why the function would run without error on one of the conditions, but then have a forking error on the other condition. The process that runs after both conditions is exactly the same.
By using print statements, I have noticed that this forking error triggers when the function tries to call the requests.get() function on the API.
If this issue is related to how I have setup the background process functionality, I would greatly appreciate some suggestions or assitance on how to do this properly, where I will not face this forking error.
If there is any information I have left out that will be helpful, please let me know and I will try to provide it.
Thank you for any help you can provide.
