In JetBrains IDEs, UI freezes are often blamed on “heavy work on the EDT,” but our recent investigations show another common culprit in plugins: long, non-cancellable read actions running in backgroun

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UI freezes in JetBrains IDEs are often caused not just by heavy work on the Event Dispatch Thread, but by long, non-cancellable read actions running in background threads. These read actions hold the platform's reader-writer lock, blocking all pending write actions and freezing the UI until they complete. The post explains the underlying locking mechanism, shows a real-world freeze example from the Package Checker plugin, and provides concrete alternatives: using cancellable read action APIs like `readAction{}` (coroutines), `ReadAction.nonBlocking{}`, or splitting work into small chunks with `ProgressManager.checkCanceled()`. It also notes that as of 2026.1, `runReadAction` and `ReadAction.compute` are being deprecated in favor of explicitly named blocking variants, encouraging plugin authors to migrate to cancellable patterns.

UI Freezes and the Dangers of Non-Cancellable Read Actions in Background Threads