[Stackless] exceptions.TypeError: arg 5 (closure) expected cell, found stackless._wrap.cell when unpickling stackless thread
Crispin Wellington
retrogradeorbit at gmail.com
Mon Oct 12 07:27:13 CEST 2009
OK. I boiled down the code to a small snippet that triggers the bug. It is a
bug that is exposed through my use of Twisted. If i create a factory, and
then two callbacks that are closures, each callback setting thread level
variables. Then I add the callbacks to the factory's deferred, and then I
sleep the threadlet forever.
Initiate the tasklet, pickle it, then unpickle it, and BAM, you have your
error:
$ /usr/local/stackless/bin/python break-stackless.py
Traceback (most recent call last):
File "break-stackless.py", line 47, in <module>
test()
File "break-stackless.py", line 37, in test
obj = pickle.loads(data)
File "/usr/local/stackless/lib/python2.6/pickle.py", line 1409, in loads
return Unpickler(file).load()
File "/usr/local/stackless/lib/python2.6/pickle.py", line 893, in load
dispatch[key](self)
File "/usr/local/stackless/lib/python2.6/pickle.py", line 1252, in
load_build
setstate(state)
TypeError: arg 5 (closure) expected cell, found stackless._wrap.cell
The code is....
-----------------------------
import stackless
import pickle
from twisted.web import client
def tasklet():
# create an example state
factory = client.HTTPClientFactory("http://www.google.com/", agent =
"stackless/1.0" )
get_complete = [False]
get_failed = [False]
def _doFailure(data):
get_failed[0] = factory.status
def _doSuccess(data):
get_complete[0] = factory.status
factory.deferred.addCallback(_doSuccess).addErrback(_doFailure)
while True:
stackless.schedule()
def test():
# run the task
task = stackless.tasklet(tasklet)
task.setup()
task.run()
# pump once
stackless.schedule()
# now serialise
data = pickle.dumps(task)
# now deserialise
obj = pickle.loads(data)
# resume
task.kill()
obj.insert()
# pump again
stackless.schedule()
if __name__=="__main__":
test()
-----------------------
If code formatting is an issue, I've attached the code to the email as a
file...
Can anyone shed any light on this bug?
Kind Regards
Crispin
On Sat, Oct 10, 2009 at 2:21 AM, Richard Tew <richard.m.tew at gmail.com>wrote:
> On Fri, Oct 9, 2009 at 10:38 PM, Crispin Wellington
> <retrogradeorbit at gmail.com> wrote:
> > I have written a server that contains stackless threads. When the server
> > shuts down these threads are serialised to disk. This all happens without
> > incident and I end up with a reasonably sized file per pickled object.
> >
> > When I go to deserialise them I hit a problem. I get this...
> > -------------------
> > File
> >
> "/home/cwellington/Development/yabi/yabi-be-twisted/trunk/TaskManager/Tasklets.py",
> > line 54, in load
> > task = pickle.loads(data)
> > File "/usr/local/stackless/lib/python2.6/pickle.py", line 1415, in
> > loads
> > return Unpickler(file).load()
> > File "/usr/local/stackless/lib/python2.6/pickle.py", line 898, in
> load
> > dispatch[key](self)
> > File "/usr/local/stackless/lib/python2.6/pickle.py", line 1258, in
> > load_build
> > setstate(state)
> > exceptions.TypeError: arg 5 (closure) expected cell, found
> > stackless._wrap.cell
> > --------------------
> >
> > I think this might be a bug. The arguments are being passed back into the
> > constructor of the stackless._wrap.function and the constructor is
> throwing
> > that exception. So in essence, the __reduce__ or __reduce_ex__ functions
> are
> > creating instatiation values that do not work on reinstantiation.
> >
> > I changed pickle.py to print out some debug. setstate is... <built-in
> method
> > __setstate__ of stackless._wrap.function object at 0x21ca0c8> and
> (state)[4]
> > is... (<cell at 0x2605f30: empty>, <cell at 0x2940718: list object at
> > 0x259f518>, <cell at 0x2940670: str object at 0x2940768>, <cell at
> > 0x2940750: str object at 0x29407d8>, <cell at 0x29407c0: int object at
> > 0x25cd338>)
> >
> > These all seem to be "cell" objects. Why aren't they
> (stackless._wrap.cell)
> > recognised as "cells"?
> >
> > I can provide a pickletools.dis() dump of the pickle stream if wanted.
> >
> > Using Stackless Python 2.6.2 on 64 bit linux (x86_64).
> >
> > Can anybody help me decode my objects? or even find a way to encode them
> so
> > the are decodable? Is this a bug, or am I doing it wrong?
>
> It definitely looks like a bug. If you can provide the smallest
> possible reproduction case, it would help us look into it and we could
> add it to the test suite as a regression test.
>
> If you want your objects back in the meantime, you might try compiling
> 2.6 with the relevant code raising these errors commented out.
>
> Richard.
>
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