Simple threading

[jrpfinch]

I'm just getting started on threading and was wondering why the
following code does not work (i know globals is bad style - I'll
eliminate them eventually). All I get is a blank cursor flashing.

Many thanks

Jon

import threading
import sys
import time
global g_datum
global g_rawfile
global g_rawtext
global g_overs
global g_currentover
global g_secondspertic k


g_secondspertic k=5
g_datum=time.ti me()
g_currenttick=1
g_rawfile=open( 'inputashes.txt ','r')
g_rawtext=g_raw file.read()
g_overs=g_rawte xt.split('<P>')
g_currentover=0


class ImapThread(thre ading.Thread):
def run(self):
global g_currenttick
if time.time() (g_datum + (g_secondsperti ck *
g_currenttick)) :
print "Ticked %s" % g_currenttick
g_currenttick=g _currenttick+1
print g_currenttick
sys.stdout.flus h()
time.sleep(0.01 )

def main():
ImapThread().st art()
while 1:
pass

if __name__ == "__main__":
main()

[hg]

Re: Simple threading

jrpfinch wrote:

I'm just getting started on threading and was wondering why the
following code does not work (i know globals is bad style - I'll
eliminate them eventually). All I get is a blank cursor flashing.
>
Many thanks
>
Jon
>
import threading
import sys
import time
global g_datum
global g_rawfile
global g_rawtext
global g_overs
global g_currentover
global g_secondspertic k
>
>
g_secondspertic k=5
g_datum=time.ti me()
g_currenttick=1
g_rawfile=open( 'inputashes.txt ','r')
g_rawtext=g_raw file.read()
g_overs=g_rawte xt.split('<P>')
g_currentover=0
>
>
class ImapThread(thre ading.Thread):
def run(self):
global g_currenttick
if time.time() (g_datum + (g_secondsperti ck *
g_currenttick)) :
print "Ticked %s" % g_currenttick
g_currenttick=g _currenttick+1
print g_currenttick
sys.stdout.flus h()
time.sleep(0.01 )
>
def main():
ImapThread().st art()
while 1:
pass
>
if __name__ == "__main__":
main()
>

Run gets called only once: you need to put your logic in a "while True"
or something equivalent/define some escape clause.

Right now you just get into the implicit "else" and get out.

hg

import time
global g_datum
global g_rawfile
global g_rawtext
global g_overs
global g_currentover
global g_secondspertic k


g_secondspertic k=5
g_datum=time.ti me()
g_currenttick=1
#g_rawfile=open ('inputashes.tx t','r')
#g_rawtext=g_ra wfile.read()
#g_overs=g_rawt ext.split('<P>' )
g_currentover=0


class ImapThread(thre ading.Thread):
def run(self):
while True:
global g_currenttick
if time.time() (g_datum + (g_secondsperti ck *
g_currenttick)) :
print "Ticked %s" % g_currenttick
g_currenttick=g _currenttick+1
print g_currenttick
sys.stdout.flus h()
else:
print 'HERE'
time.sleep(0.01 )

def main():
ImapThread().st art()
while 1:
pass

if __name__ == "__main__":
main()

[jrpfinch]

Re: Simple threading

many thanks - works perfectly now

[jrpfinch]

Re: Simple threading

Thank you for your help - the application is proceeding well.

[Gabriel Genellina]

Re: Simple threading

At Thursday 23/11/2006 12:28, jrpfinch wrote:

>I'm just getting started on threading and was wondering why the
>following code does not work (i know globals is bad style - I'll
>eliminate them eventually). All I get is a blank cursor flashing.

You've got your example already working.
Globals are bad style, but worse, threads and globals don't mix very
well: you need some sort of syncronization for accessing globals
(specially for writing them).

>class ImapThread(thre ading.Thread):
def run(self):
global g_currenttick
if time.time() (g_datum + (g_secondsperti ck *
>g_currenttick) ):
print "Ticked %s" % g_currenttick
g_currenttick=g _currenttick+1
print g_currenttick

Having more than one thread, g_currenttick could have been modified
*after* you read its value and *before* you write it back, so you
lose the count.


--
Gabriel Genellina
Softlab SRL

_______________ _______________ _______________ _____
Correo Yahoo!
Espacio para todos tus mensajes, antivirus y antispam ¡gratis!
¡Abrí tu cuenta ya! - http://correo.yahoo.com.ar

[Grant Edwards]

Re: Simple threading

On 2006-11-25, Gabriel Genellina <gagsl-py@yahoo.com.ar wrote:

>>I'm just getting started on threading and was wondering why the
>>following code does not work (i know globals is bad style - I'll
>>eliminate them eventually). All I get is a blank cursor flashing.

>
You've got your example already working. Globals are bad
style, but worse, threads and globals don't mix very well: you
need some sort of syncronization for accessing globals
(specially for writing them).

That depends on the type of the global and how they're used.
Re-binding a name is always an atomic operation. Modifying
many mutable objects is atomic.

>>class ImapThread(thre ading.Thread):
> def run(self):
> global g_currenttick
> if time.time() (g_datum + (g_secondsperti ck *
>>g_currenttick )):
> print "Ticked %s" % g_currenttick
> g_currenttick=g _currenttick+1
> print g_currenttick

>
Having more than one thread, g_currenttick could have been modified
*after* you read its value and *before* you write it back, so you
lose the count.

Right. Reading an integer object in one statement and writing
it in a subsequent statement is not an atomic opteration unless
protected by some synchronization mechanism.

--
Grant Edwards
grante@visi.com

[Aahz]

Re: Simple threading

In article <12mgkd6e5cp5l1 6@corp.supernew s.com>,
Grant Edwards <grante@visi.co mwrote:

>
>Re-binding a name is always an atomic operation. Modifying
>many mutable objects is atomic.

You know this, but just to make clear: rebinding attributes of an object
(which are also sometimes called names) is not necessarily an atomic
operation. Moreover, only a plain rebinding operation is atomic;
augmented assignment is frequently not atomic.
--
Aahz (aahz@pythoncra ft.com) <* http://www.pythoncraft.com/

"In many ways, it's a dull language, borrowing solid old concepts from
many other languages & styles: boring syntax, unsurprising semantics,
few automatic coercions, etc etc. But that's one of the things I like
about it." --Tim Peters on Python, 16 Sep 1993

[Fredrik Lundh]

Re: Simple threading

Grant Edwards wrote:

That depends on the type of the global and how they're used.
Re-binding a name is always an atomic operation. Modifying
many mutable objects is atomic.

footnote: for more on this topic, see this FAQ entry:

http://effbot.org/pyfaq/what-kinds-of-global-value-mutation-are-thread-safe.htm

and this recent python-dev thread that discusses that entry:

http://mail.python.org/pipermail/python-dev/2006-November/thread.html#69981

</F>