Re: updating variable in Parent using Parallel::ForkManager
On 2012-07-30 15:47, punit jain wrote:
my $pm = new Parallel::ForkManager(10);
my $count=0;
foreach my $user (@users) {
$pm->start($user) and next;
my $result;
--- do some processing ---
$pm->finish(0, \$result);
}
$pm->wait_all_children;
However the final value of count is not correct. Is there some race
condition on same variable updation by the processes ?
pm -> run_on_finish (
sub {
my $result = @;
if (defined($result)) {
my $count += $result;
}
}
I wonder why you expect a parent variable to be available to a child.
I am ignoring the bugs and style issues in your code, because they are
not relevant to that point.
If you need to merge results from child-processes, it is best to let
those child-processes write to unshared resources. Rows with an
autoincrement-id in a database are often fine for that. A separate file
per child-process on disk can also be fine.
After all children exited, the parent collects all those results and
merges them.
Map: the parent divides the tasks over the children
Reduce: each child reduces its assigned input to a result
Merge: the parent combines all the results into the final result
--
Ruud
--
To unsubscribe, e-mail: beginners-unsubscr...@perl.org
For additional commands, e-mail: beginners-h...@perl.org
http://learn.perl.org/
Re: updating variable in Parent using Parallel::ForkManager
punit jain wrote:
Hi,
Hello,
I am facing an issue. Below is code snippet : -
my $pm = new Parallel::ForkManager(10);
my $count=0;
foreach my $user (@users) {
$pm->start($user) and next;
my $result;
--- do some processing ---
$pm->finish(0, \$result);
}
$pm->wait_all_children;
However the final value of count is not correct. Is there some race
condition on same variable updation by the processes ?
Regards,
Punit
pm -> run_on_finish (
sub {
my $result = @;
if (defined($result)) {
my $count += $result;
Here you are creating a variable named $count which is only visible
inside the scope of this subroutine, so your other $count variable is
not affected.
}
}
John
--
Any intelligent fool can make things bigger and
more complex... It takes a touch of genius -
and a lot of courage to move in the opposite
direction. -- Albert Einstein
--
To unsubscribe, e-mail: beginners-unsubscr...@perl.org
For additional commands, e-mail: beginners-h...@perl.org
http://learn.perl.org/
Re: updating variable in Parent using Parallel::ForkManager
Hi Punit,
On Mon, 30 Jul 2012 19:17:21 +0530
punit jain wrote:
> Hi,
>
>
> I am facing an issue. Below is code snippet : -
>
It is a good idea to include a self-contained reproducing code that will
demonstrate the problem - not incomplete snippets.
> my $pm = new Parallel::ForkManager(10);
>
> my $count=0;
>
> foreach my $user (@users) {
>
>$pm->start($user) and next;
>
>my $result;
>
> --- do some processing ---
>
>$pm->finish(0, \$result);
>
> }
>
>
>
> $pm->wait_all_children;
>
>
> However the final value of count is not correct. Is there some race
> condition on same variable updation by the processes ?
>
> Regards,
> Punit
>
>
>
> pm -> run_on_finish (
>
>sub {
>
>my $result = @;
>
>if (defined($result)) {
>
>my $count += $result;
>
This is wrong - $count will be a lexical variable only present inside its
scope. You should declare it global to the scope - outside the anonymous
subroutine:
<<<
my $count = 0;
$pm->run_on_finish(
sub {
$count += $result;
}
);
>>>
For more information see:
http://perl.plover.com/FAQs/Namespaces.html
Regards,
Shlomi Fish
--
-
Shlomi Fish http://www.shlomifish.org/
Freecell Solver - http://fc-solve.shlomifish.org/
I’d do Windows-- , but this may result in an integer underflow.
— an Israeli Linuxer.
Please reply to list if it's a mailing list post - http://shlom.in/reply .
--
To unsubscribe, e-mail: beginners-unsubscr...@perl.org
For additional commands, e-mail: beginners-h...@perl.org
http://learn.perl.org/
