Error in worker: NoModificationAllowedError: Failed to execute 'removeEntry'

[xvrh]

In Chrome with cross-origin isolation, we are seeing this error when multiple tabs are open. We use some powersync & sqlite_async databases.

NoModificationAllowedError: Failed to execute 'removeEntry' on 'FileSystemDirectoryHandle': An attempt was made to modify an object where modifications are not allowed.

When that error arises, we observe various behaviors. Sometimes it's benign, but sometimes it poisons the database and we have to go to chrome://inspect to kill the Shared Worker.

We worked around it with custom navigator.locks and retry logic, but I'm not really confident in that approach.

We are not able to reliably reproduce the "bad behaviors", but we can easily trigger the error itself. Hopefully this helps.

Repro: https://github.com/xvrh/sqlite3_web-dual-tab-repro

[m13v]

this is the OPFS multi-tab WAL contention pattern. SharedWorker is supposed to serialize access but cross-origin isolation changes the lifecycle and you end up with two workers racing on the same FileSystemDirectoryHandle, usually around lock file cleanup or VFS journal rotation. removeEntry throwing NoModificationAllowedError is almost always 'another handle still has it open'. navigator.locks plus retry is the right shape, the missing piece is usually a single-flight election so only one tab owns writes and the others proxy through BroadcastChannel. wa-sqlite's OPFSCoopSyncVFS handles this more cleanly than the older sync-access-handle path.

[simolus3]

I can reproduce the issue, I think it's because of the temporary file handle we create for feature detection. The lack of stack traces doesn't help here, I need to see if there's a better way to debug this :D