spawn or fork

[C Gillespie]

Dear All,

I have a function
def printHello():
fp = open('file','w' )
fp.write('hello ')
fp.close()

I would like to call that function using spawn or fork. My questions are:

1. Which should I use
2. How do I call that function if it is defined in the same file.

Many thanks

Colin

[Miki Tebeka]

Re: spawn or fork

Hello Colin,
[color=blue]
> I have a function
> def printHello():
> fp = open('file','w' )
> fp.write('hello ')
> fp.close()
>
> I would like to call that function using spawn or fork. My questions are:
>
> 1. Which should I use[/color]
spawn and fork are very different functions. Read the documentation on
each.
Note the "fork" is available only in Unix like systems.
[color=blue]
> 2. How do I call that function if it is defined in the same file.[/color]
Just call it.

def foo():
print 1

foo()

Bye.
--
------------------------------------------------------------------------
Miki Tebeka <miki.tebeka@zo ran.com>

http://tebeka.bizhat.com

The only difference between children and adults is the price of the toys

[C Gillespie]

Re: spawn or fork


"Miki Tebeka" <miki.tebeka@zo ran.com> wrote in message
news:mailman.73 59.1102503309.5 135.python-list@python.org ...[color=blue]
> Hello Colin,
>[color=green]
> > I have a function
> > def printHello():
> > fp = open('file','w' )
> > fp.write('hello ')
> > fp.close()
> >
> > I would like to call that function using spawn or fork. My questions[/color][/color]
are:[color=blue][color=green]
> >
> > 1. Which should I use[/color]
> spawn and fork are very different functions. Read the documentation on
> each.
> Note the "fork" is available only in Unix like systems.
>[color=green]
> > 2. How do I call that function if it is defined in the same file.[/color]
> Just call it.
>
> def foo():
> print 1
>[/color]
Thanks, but can I call it using spawn?

[Eric Brunel]

Re: spawn or fork

C Gillespie wrote:[color=blue]
> Dear All,
>
> I have a function
> def printHello():
> fp = open('file','w' )
> fp.write('hello ')
> fp.close()
>
> I would like to call that function using spawn or fork. My questions are:
>
> 1. Which should I use
> 2. How do I call that function if it is defined in the same file.[/color]

spawn execute an external executable program *outside* your current script,
*not* a Python function. So say you want to run wordpad.exe from your Python
script, you could do:

os.spawn(os.P_N OWAIT, "C:\\Progra m files\\Accesori es\\wordpad.exe , [...])

So you *need* an external executable to be passed to spawn.

fork works another way: it duplicates the context of your process in another one
and continues both processes in parallel. So basically, it doesn't *execute*
anything, but just creates a process. You may then call your function is the new
process (a.k.a the "child" process):

def printHello():
...
if os.fork() == 0:
## fork returns 0 in the process copy => this is where we call our function
printHello()
else:
## If fork doesn't return 0, we're in the original => other code
...

However, fork is only available on Unices.

What are you trying to do exactly? If you provide more explanations, we may
provide a better help than the simplistic one above.

HTH
--
- Eric Brunel <eric (underscore) brunel (at) despammed (dot) com> -
PragmaDev : Real Time Software Development Tools - http://www.pragmadev.com

[Diez B. Roggisch]

Re: spawn or fork

> Thanks, but can I call it using spawn?

No, but you can spawn a python interpreter that calls it. Like this:

spawnv(P_<whate ver>, sys.executable, ['-c', 'import myfile; foo()'])

But I suggest you use fork - then you can call it in the interpreter itself.
--
Regards,

Diez B. Roggisch

[C Gillespie]

Re: spawn or fork

[color=blue]
> What are you trying to do exactly? If you provide more explanations, we[/color]
may[color=blue]
> provide a better help than the simplistic one above.[/color]
Dear All,

Thanks for the suggestions.

Basically, I have the situation where a user (via the web) requests data
from a database that has to be written to file. However, this takes a couple
of minutes. So the way I thought of doing this is:
1. create an empty file.
2a. tell the user where to look for the file.
2b. spawn a process to insert data into the file.

This way the user can see the data as its being written.

Thanks

Colin

[Eric Brunel]

Re: spawn or fork

C Gillespie wrote:[color=blue][color=green]
>>What are you trying to do exactly? If you provide more explanations, we[/color]
>
> may
>[color=green]
>>provide a better help than the simplistic one above.[/color]
>
> Dear All,
>
> Thanks for the suggestions.
>
> Basically, I have the situation where a user (via the web) requests data
> from a database that has to be written to file. However, this takes a couple
> of minutes. So the way I thought of doing this is:
> 1. create an empty file.
> 2a. tell the user where to look for the file.
> 2b. spawn a process to insert data into the file.
>
> This way the user can see the data as its being written.[/color]

You may want to use threads for this instead of processes. See

http://docs.python.org/lib/module-threading.html

HTH
--
- Eric Brunel <eric (underscore) brunel (at) despammed (dot) com> -
PragmaDev : Real Time Software Development Tools - http://www.pragmadev.com

[sjdevnull@yahoo.com]

Re: spawn or fork

Eric Brunel wrote:[color=blue][color=green]
> > Basically, I have the situation where a user (via the web) requests[/color][/color]
data[color=blue][color=green]
> > from a database that has to be written to file. However, this takes[/color][/color]
a couple[color=blue][color=green]
> > of minutes. So the way I thought of doing this is:
> > 1. create an empty file.
> > 2a. tell the user where to look for the file.
> > 2b. spawn a process to insert data into the file.
> >
> > This way the user can see the data as its being written.[/color]
>
> You may want to use threads for this instead of processes. See
> http://docs.python.org/lib/module-threading.html[/color]

I haven't seen any reason he wants to give up protected memory, so the
only reason to use threads is if the platform doesn't support fork (or
has a broken/nonperformant implementation thereof).