PipelineError during backup

[francois]

I'm using a fresh darcs checkout as of November 24 with Alberto Berti's patches for #641 applied.

A 'tahoe backup' run, sometimes crash with the following exception.

2009-11-24 09:38:21+0100 [Negotiation,client] Unhandled error in Deferred:
2009-11-24 09:38:21+0100 [Negotiation,client] Unhandled Error
        Traceback (most recent call last):
          File "/usr/lib/python2.4/site-packages/Twisted-8.1.0-py2.4-linux-i686.egg/twisted/internet/defer.py", line 312, in _startRunCallbacks
            self._runCallbacks()
          File "/usr/lib/python2.4/site-packages/Twisted-8.1.0-py2.4-linux-i686.egg/twisted/internet/defer.py", line 328, in _runCallbacks
            self.result = callback(self.result, *args, **kw)
          File "/usr/lib/python2.4/site-packages/Twisted-8.1.0-py2.4-linux-i686.egg/twisted/internet/defer.py", line 289, in _continue
            self.unpause()
          File "/usr/lib/python2.4/site-packages/Twisted-8.1.0-py2.4-linux-i686.egg/twisted/internet/defer.py", line 285, in unpause
            self._runCallbacks()
        --- <exception caught here> ---
          File "/usr/lib/python2.4/site-packages/Twisted-8.1.0-py2.4-linux-i686.egg/twisted/internet/defer.py", line 328, in _runCallbacks
            self.result = callback(self.result, *args, **kw)
          File "/root/tahoe/src/allmydata/immutable/encode.py", line 481, in _remove_shareholder
            level=log.UNUSUAL, failure=why)
          File "/root/tahoe/src/allmydata/immutable/encode.py", line 99, in log
            return log.msg(*args, **kwargs)
          File "/root/tahoe/support/lib/python2.4/site-packages/foolscap-0.4.2-py2.4.egg/foolscap/logging/log.py", line 197, in msg
            f2.setCopyableState(fs.getStateToCopy(f, FakeBroker))
          File "/root/tahoe/support/lib/python2.4/site-packages/foolscap-0.4.2-py2.4.egg/foolscap/call.py", line 796, in getStateToCopy
            state['value'] = str(obj.value) # Exception instance
        exceptions.AttributeError: PipelineError instance has no attribute 'args'

[zooko]

Marking this as potentially a regression from v1.5.

[zooko]

Brian, could you look at this?

I really don't understand this part:

          File "/root/tahoe/support/lib/python2.4/site-packages/foolscap-0.4.2-py2.4.egg/foolscap/call.py", line 796, in getStateToCopy
            state['value'] = str(obj.value) # Exception instance
        exceptions.AttributeError: PipelineError instance has no attribute 'args'

There is no attempt to access an attribute named 'args' on that line, so how can there be an AttributeError on 'args'?

[warner]

I think the problem is that PipelineError is not str-able (it overrides __init__ and __repr__ but not __str__).

If I had to guess, I'd say that a connection was lost during the upload, the encoder tried to log.msg the exception instance, but it wasn't str-able so it blew up. I'd also guess that this has been a problem since that Pipeline class went into 1.5.0, but only shows up if you get an exception during upload.

I'll add a test of str-ability and fix the class (source:src/allmydata/util/pipeline.py in case anyone's curious).

[warner]

hrm, I'm not seeing the test fail on my py2.6 system. Maybe py2.5 or py2.6 started implementing str() in terms of repr(), thus masking the problem?

[warner]

Ok, 41bcc9f39ec52c7e should close this. Python2.5/2.6 don't suffer from the problem, but py2.4 does. francois: could you check that test_util.Pipeline passes with the new patch? If so, this problem should be resolved.

[francois]

Wouah, that was fast, thanks Brian.

And, yes, the unit test passed on my old Debian etch machine.