Open Radar

 
Summary:
The attached sample project runs into a deadlock, as soon as TimeMachine is performing a backup.

To explain it:

- The project creates two NSFilePresenter for the file "~/Desktop/presenter-problem.txt"
- One file presenter is constantly writing a file (as coordinated write)
- The other file presenter is just waiting for changes through -presentedItemDidChange (coordinated, with NSFileCoordinatorReadingWithoutChanges)

Both file presenter implement at least one of the callback delegates (e.g. -relinquishPresentedItemToReader:).

If Time Machine is not performing backups, the sample app works: One presenter is writing, the other is reading. You'll see a progressing output on the Console.

However, if Time Machine is performing backups, the app hangs while attempting to perform a coordinated read or a coordinated write (in -updateContents and presentedItemDidChange). 

I've attached sysdiagnose logs. Please have a special look at "filecoordination-dump.txt", which shows that the subarbiter "backupd" is somehow invovled in the file lock.

Steps to Reproduce:
1. Start a Time Machine backup and wait until the actual backup starts (the Time Machine menu should show "Backing up: X of Y MB")
2. Start the sample app


Expected Results:
The sample app should show an infinite loop of write operations and read operations.

Actual Results:
Only a few write / read operations are performed. After some steps, the app stops and hangs forever in -updateContents and -presentedItemDidChange.