Question: Threading and embedding python in an application

[David Harrison]

Thanks very  much for the responses.  I did indeed look carefully
at the code I was using for threading and didn't see anything
obvious.  I include the python excerpt below.  For small values
of lMax, things seem to work as expected.  Larger values seem
to cause the thread to either hang or terminate (I can't tell which one).

If threading in an imported module is questionable, is there another
way I can use python threads without python being directly
in control?

# -----

import time
import threading

def computation(pFp):
    print >>pFp, "computation starting"
    lStart = time.time()
    lSum = 0
    lMax = 1000000
    for lSlot in xrange(0,lMax):
        if (lSlot % 2) == 0:
            lSum += lSlot
        else:
            lSum -= lSlot
    lEnd = time.time()
    print >>pFp, "Sum is", lSum
    print >>pFp, "Time is", lEnd-lStart, "seconds"

class MyThread(threading.Thread):
    def __init__(self, pLog):
        threading.Thread.__init__(self, name="Compute")
        self.mLog = pLog
    def run(self):
        lFp = open(self.mLog, "a")
        print >>lFp, "This is run", self
        computation(lFp)
        lFp.close()

t = MyThread("/var/tmp/big.log")
t.start()


On 2005-05-10 12:48:36 -0700, Mike Meyer <mwm at mired.org> said:

> David Harrison <daha at best.com> writes:
> 
>> I am working on an application on Mac OS X that calls out
>> to python via PyImport_ImportModule().  I find that if
>> the imported module creates and starts a python thread,
>> the thread seems to be killed when the import of
>> the module is complete.   Is this expected?  Does
>> python have to be in control to allow threads to run?
> 
> Having an imported module create a thread is a bad idea. For one
> thing, the thread won't get created if the module is imported a second
> time. While this may be the desired behavior, it can also be
> surprising. For another, there are known behaviors in the Python
> threading code that can cause deadlocks when you do this. I say
> "behaviors" instead of "bugs", because the last time this came up,
> there was no indication that anyone was interested in fixing this.
> 
>       <mike