Hey everyone, I’m having some trouble with a Haskell file watcher I made using the Twitch package. It’s supposed to copy JS files from a ‘central’ folder to ‘back’ and ‘front’ folders. The code works, but it’s running twice for each file.
Here’s what’s happening:
Copied file central\models\Board\Board.js to back and front
Copied file central\models\Board\Board.js to back and front
I’ve encountered similar issues with file watchers in Haskell before. It sounds like you might be dealing with a race condition or multiple event triggers. Have you tried adding a debounce mechanism to your watcher? This can help prevent multiple executions for a single file change.
Another thing to check is your file system events. Some systems emit multiple events for a single file operation, which could explain the duplicate runs. You might want to look into using a more robust file watching library like ‘fsnotify’ instead of Twitch, as it handles these edge cases better.
For the garbled output, that definitely seems like a concurrency issue. Try adding some synchronization to your file copying process. As for the ‘cabal v2-run’ problem, make sure you’re not relying on any specific working directory in your code, as running it as a background process might change the context.
hey mate, i’ve seen this before. twitch can be a bit finicky with file events. try adding a small delay between file operations, like a Thread.sleep or something. that might stop the double-firing.
for the weird output, looks like a concurrency thing. maybe use Control.Concurrent.MVar to sync your writes?
I’ve dealt with similar issues using Twitch for file watching. One thing that helped me was implementing a simple caching mechanism. Basically, keep track of the last modified time for each file you’re watching. When an event triggers, check if the file’s current modification time is different from the cached one. If it is, process the file and update the cache. If not, skip it.
This approach helped eliminate most of the duplicate processing in my projects. For the garbled output, you might want to look into using something like Control.Concurrent.Chan to queue up your file operations and process them sequentially. This should prevent the output from getting mixed up.
As for the background execution issue, make sure you’re using absolute paths in your code instead of relative ones. This ensures your program works correctly regardless of the working directory. Hope this helps you out!
This issue often stems from how file systems handle events. Some generate multiple notifications for a single change, leading to duplicate executions. To mitigate this, consider implementing a cooldown period after each file operation.
You could use a simple timestamp check before processing each event. Store the last processed time for each file and only proceed if a certain interval has passed. This approach can significantly reduce redundant operations.
Regarding the garbled output, it’s likely due to concurrent writes to stdout. Implement proper locking mechanisms when writing to the console to ensure thread safety.
For the background execution problem, ensure your program doesn’t rely on the current working directory. Use absolute paths or environment variables to specify file locations. This should resolve issues when running the program in different contexts.
I’ve encountered similar challenges with Haskell file watchers. One effective approach is to implement a simple throttling mechanism. You can use Data.Time to record the last processing time for each file and only proceed if a certain interval has elapsed since the last operation.
For the garbled output, consider using Control.Concurrent.Chan to queue file operations and process them sequentially. This should resolve the concurrency issues causing mixed output.
Regarding the background execution problem, ensure you’re using absolute paths throughout your code. Relying on relative paths can cause issues when the working directory changes. You might also want to look into using the ‘directory’ package for more robust file path handling.
Lastly, if Twitch continues to be problematic, consider switching to a more stable file watching library like ‘fsnotify’. It often provides better handling of complex file system events.