Renderer unresponsive (6-7s freeze) in execEditLength when computing large file diffs #32853

Activity

1. github-actions

   assigned

   Hona

   on Jun 18, 2026
2. github-actions commented on Jun 18, 2026

   

   github-actionsBot

   on Jun 18, 2026 – with GitHub Actions

   Contributor

   More actions

   This issue might be a duplicate of existing issues. Please check:

   • Desktop v1.16.0 Windows: renderer unresponsive / UI freeze when computing diff of large files #30906: Desktop renderer unresponsive / UI freeze when computing diff of large files (Windows)
   • Renderer freezes / "app not responding" when computing large diffs #32046: Renderer freezes / "app not responding" when computing large diffs
   • The opencode Desktop UI freezes for approximately 10–12 seconds when rendering file diffs. #31195: Desktop UI freezes for approximately 10–12 seconds when rendering file diffs
   • Desktop app renderer freezes/crashes repeatedly #31594: Desktop app renderer freezes/crashes repeatedly

   If your issue is distinct from the above, please add context explaining how it differs.
3. rafaelgou commented on Jul 2, 2026

   

   rafaelgou

   on Jul 2, 2026

   Last edited by rafaelgou

   More actions

   It seems I have the same issue Opencode GUI on Ubuntu 24.04.

   I used MiMo v2.5 on Opencode TUI to analyse the logs and generate a report. I hope it's useful.

   Full report attached.

   opencode-debug-20260702T130622.zip

   ---

   Renderer Unresponsive: Synchronous Diff Computation Blocks UI Thread

   Environment

   • OpenCode version: 1.17.13 (packaged)
   • Platform: Linux x64 (also confirmed on Windows 11 — see Renderer unresponsive (6-7s freeze) in execEditLength when computing large file diffs #32853)
   • Electron: 42.3.3 / Chrome 148.0.7778.218
   • Node: 24.15.0
   • Uptime before freeze: ~22 seconds from app start

   Symptoms

   • GUI freezes completely, Electron marks renderer as "unresponsive"
   • Multiple sessions across several days reproduced the same freeze (10+ dump directories in logs)
   • One session recovered after ~6s; others required force-quit
   • ResizeObserver loop completed with undelivered notifications in renderer.log confirms UI thread saturation

   Root Cause

   The diff npm package (used for computing unified diffs) runs synchronously on the renderer main thread inside a SolidJS reactive computation. When a session contains a large file diff, the O(n*m) Myers diff algorithm blocks the main thread for seconds, triggering Electron's unresponsive detector.

   Stack Trace (from window.log)

   renderer unresponsive {
     window: '7ea1ad21-534f-42be-8c90-1c807b0d021c',
     currentURL: 'oc://renderer/index.html'
   }
   
   renderer unresponsive samples
   Window: 7ea1ad21-534f-42be-8c90-1c807b0d021c
   URL: oc://renderer/index.html
   <2>
       at execEditLength (main-C--ziyJW.js:44377:7)
       at LineDiff.diffWithOptionsObj (main-C--ziyJW.js:44426:21)
       at LineDiff.diff (main-C--ziyJW.js:44347:17)
       at diffLines (main-C--ziyJW.js:44577:19)
       at structuredPatch (main-C--ziyJW.js:44619:35)
       at createTwoFilesPatch (main-C--ziyJW.js:44749:22)
       at parseDiffFromFile (main-C--ziyJW.js:44776:32)
       at fileDiffFromContent (main-C--ziyJW.js:137831:10)
       at fileDiffFromPatch (main-C--ziyJW.js:137765:28)
       at resolveFileDiff (main-C--ziyJW.js:137735:47)
       at normalize (main-C--ziyJW.js:137748:15)
       at main-C--ziyJW.js:145033:8
       at Proxy.map (<anonymous>)
       at Object.fn (main-C--ziyJW.js:145032:74)
       at runComputation (main-C--ziyJW.js:487:22)
       at updateComputation (main-C--ziyJW.js:470:3)
       at Object.readSignal (main-C--ziyJW.js:403:67)
       at diff2 (main-C--ziyJW.js:145247:41)
       at diffCanRender (main-C--ziyJW.js:145248:49)
       at get value (main-C--ziyJW.js:145362:32)
       at Array.resolveSources (main-C--ziyJW.js:963:24)
       at isExpanded (main-C--ziyJW.js:116706:48)
       at get open (main-C--ziyJW.js:116721:18)
       at Array.resolveSources (main-C--ziyJW.js:963:24)
       at open (main-C--ziyJW.js:108733:23)
       at access$1 (main-C--ziyJW.js:8319:67)
       at Object.value (main-C--ziyJW.js:9675:18)
       at Object.fn (main-C--ziyJW.js:9647:54)
       at runComputation (main-C--ziyJW.js:487:22)
       at updateComputation (main-C--ziyJW.js:470:3)
       at createMemo (main-C--ziyJW.js:119:3)
       at createControllableSignal$1 (main-C--ziyJW.js:9647:24)
       at createControllableBooleanSignal (main-C--ziyJW.js:9664:31)
       at createDisclosureState (main-C--ziyJW.js:9674:31)
       at CollapsibleRoot$1 (main-C--ziyJW.js:108732:27)
   

   Call Chain Analysis

   The freeze path is:

   1. CollapsibleRoot (file diff collapsible section) mounts
   2. createDisclosureState → createControllableBooleanSignal creates reactive state
   3. isExpanded getter triggers diffCanRender → diff2
   4. diff2 reads resolveSources signal which calls resolveFileDiff → normalize
   5. normalize calls fileDiffFromContent → parseDiffFromFile → createTwoFilesPatch
   6. createTwoFilesPatch → structuredPatch → diffLines → LineDiff.diff
   7. LineDiff.diff runs execEditLength — the O(n*m) Myers algorithm — synchronously on the main thread

   The entire diff computation is wrapped in runComputation, meaning it re-executes on any reactive dependency change with no debouncing, no lazy evaluation, and no web worker offloading.

   Reproducibility

   This exact stack trace appeared in 10+ separate session dumps across Jun 30 – Jul 2, 2026:

   Session	Date	Result
   20260630T122440	Jun 30	renderer.log present
   20260701T144943	Jul 1 14:49	crash.log
   20260701T165125	Jul 1 16:51	crash.log
   20260701T170005	Jul 1 17:00	crash.log
   20260701T174224	Jul 1 17:42	crash.log
   20260701T233829	Jul 1 23:38	crash.log
   20260701T234841	Jul 1 23:48	window.log: unresponsive, same stack
   20260701T234908	Jul 1 23:49	crash.log
   20260702T000115	Jul 2 00:01	crash.log
   20260702T000134	Jul 2 00:01	crash.log
   20260702T000228	Jul 2 00:02	window.log: unresponsive (recovered)
   20260702T002125	Jul 2 00:21	crash.log
   20260702T002211	Jul 2 00:22	crash.log
   20260702T130558	Jul 2 13:05	window.log: unresponsive, same stack

   Suggested Fix Directions

   1. Offload diff computation to a Web Worker — move createTwoFilesPatch / structuredPatch off the main thread entirely
   2. Lazy/deferred evaluation — only compute the diff when the collapsible section is expanded, not eagerly in a reactive computation
   3. Debounce diff computation — avoid recomputing on every reactive dependency change
   4. Virtualize large diffs — render only visible hunks, compute diff per-hunk on demand
   5. Size guard — skip visual diff for files above a threshold (e.g. >10k lines), show a "file too large for diff" message instead
4. github-actions commented on Sep 1, 2026

   

   github-actionsBot

   on Sep 1, 2026 – with GitHub Actions

   Contributor

   More actions

   To stay organized issues are automatically closed after 60 days of no activity. If the issue is still relevant please open a new one.
5. github-actions

   closed this as not plannedon Sep 1, 2026