I think I have found the problem.
It turns out that the closing and opening of the pipe is in the wrong place.
This code actually works:
#!/bin/env perl
#
use strict;
use FileHandle;
# Global variables;
my $child = 0;
my $max_child = 60;
# ------- Sub routines -------------------------------------
sub SpawnChild
{
my ($no, $child) = @_;
my $pid = fork(); # Fork a new child process
if ($pid) { # This is the parent
process
return;
}
else { # this is the child
my $sleep = 0; #int(rand(3)+1); # a no use random work load
sleep($sleep);
print WRITE "Child $no Slept $sleep\n";
exit;
}
}
sub Parent
{
my ($max_iterations) = @_;
for (my $i = 1; $i < $max_iterations; $i++) {
$child++;
print STDOUT "Parent $i $child\n";
SpawnChild($i, $child);
while ($child >= $max_child) {
my $input = <READ>;
print STDOUT $input; # print the input from
the child
$child--;
}
}
while ($child > 0) { # after the main loop
has finished
my $input = <READ>; # some child processes
are still running
print STDOUT $input; # wait for them
$child--;
}
}
# -------- Main code ----------------------------------------
pipe(READ, WRITE); # open a pipe
autoflush WRITE 1;
Parent(1000);
close READ;
close WRITE;
# -------- End ----------------------------------------------
I have ran this dozens of time and it seems it always works.
I hope somebody else can use this, might (s)he stumble upon multiprocessing
Cheers,
Jeroen
> Sent: 26 June 2003 17:55
> To: '[EMAIL PROTECTED]'
> Subject: IPC with parent from mutiple children
>
>
> Hi all,
>
> Again, I drown in the muddy watters of child processes:
>
> What I want to achieve is: spawn up to $max_child processes
> and setup pipes in such away that all child processes can
> 'print' to the parent. This because I want to inform the
> parent about the exit value of the process
> (I know I can set up a signal handler for that, but I have
> found them very unreliable, so I want to trry it using pipes)
>
> My output is not what I expected :( Can somebody help me??
>
> This is the code:
>
> #!/bin/env perl
> #
>
> use strict;
> use FileHandle;
>
> # Global variables;
> my $child = 0;
> my $max_child = 4;
>
> sub SpawnChild
> {
> my ($no, $child) = @_;
>
> pipe(READ, WRITE);
> autoflush WRITE 1;
>
> # Fork a new child process
> my $pid = fork();
> if ($pid) {
> # This is the parent process
> close(WRITE);
> return;
> }
> else { # this is the child
> close(READ);
>
> my $sleep = int(rand(6)+1); # a no use random work load
> sleep($sleep);
> print WRITE "End $no Slept $sleep\n";
> exit;
> }
> }
>
>
> sub Parent
> {
> my ($max_iterations) = @_;
>
> for (my $i = 1; $i < $max_iterations; $i++) {
> $child++;
>
> print STDOUT "Spawn $i $child\n";
> SpawnChild($i, $child);
>
> while ($child >= $max_child) {
> my $input = <READ>;
> print STDOUT $input;
> $child--;
> }
> }
> for (my $i = 1; $i < $max_child; $i++) {
> my $input = <READ>;
> print STDOUT $input;
> $child--;
> }
> }
>
> This is my output:
>
> Spawn 1 1
> Spawn 2 2
> Spawn 3 3
> Spawn 4 4
> End 4 Slept 6
> Spawn 5 4
> End 5 Slept 2
> Spawn 6 4
> End 6 Slept 1
> Spawn 7 4
> End 7 Slept 1
> Spawn 8 4
> End 8 Slept 2
> Spawn 9 4
> End 9 Slept 5
>
> So I miss something like
> End 1 Slept 6
> End 2 Slept 3
> End 3 Slept 2
> End 4 Slept 4
>
> Where did the 'return print' for the first 4 children go????
>
> Thanks for any suggestions
>
> Jeroen Lodewijks
>
>
>
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