Assertion error and stalled commit when concurrently committing the same file in different sessions

What steps will reproduce the problem?
1. Create two sessions, "session1" and "session2". 
2. Check out to two workdirs with the respective names.
3. Add some files to the workdirs, and make sure to add the same files in both 
workdirs. Add enough files to the workdirs so that it will take some time to 
commit (ensuring concurrent access). 
4. Commit both workdirs at the same time.

What is the expected output? What do you see instead?
Both commits should succeed, as they are in different sessions. Instead, only 
the commit first to finish will succeed. The other one will fail with an 
assertion error:

  File "common.py", line 179, in move_file
    assert not os.path.exists(destination)

This error occurs after the new snapshot has been consolidated, which causes 
the same error to occur again every time the repository is accessed, as the 
processing queue remains. 

A workaround to restore the repository is to manually delete the contents of 
the "queue" directory. This removes the failed commit.

Original issue reported on code.google.com by ekb...@gmail.com on 9 Mar 2012 at 10:20

harmy / boar

Assertion error and stalled commit when concurrently committing the same file in different sessions #70