JetBrains details a multi-year engineering effort to improve UI responsiveness in IntelliJ-based IDEs by moving write actions off the UI thread (EDT). The platform's 25-year-old architecture relied on a single read-write lock tightly coupled to the EDT, causing freezes when expensive write actions (like VFS refresh or PSI rebuilding) blocked the UI. The team introduced background write actions, a new cancelable lock, modality-aware locking, and incremental migration strategies to preserve plugin compatibility. Results show the expected share of UI time spent on write locks dropped from 1.83% to 0.53% between releases 2025.2 and 2025.3. Future work targets eliminating write-intent locking from common interactions like typing.
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The deadly entanglementWith good intentionsThe grand refactoringWhen one lock is not enoughMoving work without breaking pluginsLet’s do it laterResults, future work, and acknowledgmentsSort: