[Jython-users] Import issues when multi threaded

[Guy Gascoigne-P. <gg...@tr...>]

I've got a very obscure problem that I've run out of ideas with and so I'm
hoping that someone here might be able to shed some light upon it.
 
We use jython in a multithreaded script execution engine.  In simple terms
we run many scripts concurrently using multiple PythonInterpreters, one per
thread, managing thread and interpreter usage via thread pools etc.
 
Here's a description of the test harness that I've got running that will
eventually trigger the bug:
 
We have a number of library scripts something like this:
 
---
n_0.py
 
class device:
    def name(self):
        return "0"
 
---
n_1.py
 
class device:
    def name(self):
        return "1"
---
 
Then we have a number of main scripts:
 
---
r_0.py
 
dev = device.device()
print dev.name()
 
---
r_1.py
 
dev = device.device()
print dev.name()
 
---
 
The intent here is that we have a system that applies rules to targets, but
does so in such a way that the same rule can be applied to several targets
types.  To manage this, when we come to execute this we effectively do an
 
    import n_1 as device
 
and then execute r_1
 
In an ideal world this should result in the number 1 being printed on
standard out.  I do this over about 100 scripts running with 20 threads in a
pool and it works correctly, however every now and again (about 5% of the
time) I start getting the wrong results.  It appears that under some
circumstances the import line doesn't work and the interpreter picks up a
previous value for the import definition.
 
Has anyone seen anything like this before or have any suggestions as to
where to look to fix this?
 
Guy
 
-- 
"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are, by
definition, not smart enough to debug it." - Brian W. Kernighan