Embedded Python : Why does thread lock here?

[Gabriel Genellina]

En Tue, 07 Jul 2009 15:01:17 -0300, roschler <robert.oschler at gmail.com>  
escribió:

> I have the Python Intepreter embedded in a Delphi (Object Pascal)
> program.  In the Python script shown below, I have a module that
> creates a thread object and starts it.

Do you *execute* the module or do you *import* it?
Isn't a good idea to spawn a thread by side effect of importing a module.

> The thread's run() call calls
> a function called deleteOutputVariables() declared at the module
> level.  In my code's first incarnation the thread's run() call would
> deadlock when trying to call the deleteOutputVariables() function
> declared at Module level.  I would never see the statement
> "(deleteOutputVariables) Top of Call" printed to the screen.  I now
> know that I must periodically call join() with a very fast time-out to
> keep Python threads happy, and that solved the problem.

What does the Delphi code? Isn't a join with a long timeout enough?

> However I am
> curious as to why it deadlocked at the deleteOutputVariables() call?
> Is it because deleteOutputVariables() is declared at the module level
> or because that function deletes module level variables?  If so why?

I don't know, but you can make some experiments - move te  
deleteOutputVariables as a method, or don't delete module level variables  
at all, and see what happens. I'd say both factors are irrelevant.

> # FUNCTION: Delete the variables given in the list.
> def deleteOutputVariables(theModule, theOutputVariablesListOfNames):
>     try:
>         print "(deleteOutputVariables) Top of call."
>         for theOutputVariableName in theOutputVariablesListOfNames:
>             if theModule.__dict__.has_key(theOutputVariableName):
>                 print "(Python::deleteOutputVariables) Deleting the
> Output Variable named " + theOutputVariableName
>                 del theModule.__dict__[theOutputVariableName]
>     except:
>         print "(deleteOutputVariables) Exception occurred."

As a rule, avoid using __special__ names. There is almost never need of  
using them (__init__ is a notable exception) unless you want to change  
Python behaviour.
In this case:

for theOutputVariableName in theOutputVariablesListOfNames:
   if hasattr(theModule, theOutputVariableName):
     delattr(theModule, theOutputVariableName)

(a name like theOutputVariablesListOfNames is too long for my taste, but  
that's a matter of style...)

> theNewThread = None
> theNewThread = threadRun("TestThread")

That first line is useless...

-- 
Gabriel Genellina