• perldoc -q fork
• perldoc -q wait
• perldoc -q waitpid
• perldoc -q kill
• perldoc perlipc

I would have a parent start two (or more) children. As soon as the first one terminates, it would send a suitable signal to the other one(s).

Update: in the above the emphasized "it" should refer to "the parent", although as jdhedden pointed out it seems to refer to "the first one". Apologies.

It would be a bit difficult for two childred to signal each other as they wouldn't know the other's PID. Better to have child and parent handle the two tasks: The parent gets the child's PID from the fork() call, and the child can get the parent's PID using ppid().

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Remember: There's always one more bug.

That's what I meant. I guess... ;-)

I agree with blazar's basic approach.

One thing about your problem. Why burn bandwidth on parallel downloads when you're going to give up on the slower one? I don't understand what that design gets you.

this is only to simplify my question, i have 2 complex process and i don't know how to use the thread method and to monitor the status and kill

With threads, just run each process in it's own thread and then use exit to terminate. Whichever finishes first will terminate the other thread automatically.

#! perl slw
#use 5.008008; For "no warnings 'threads'" ## Doesn't work?
use strict;
use threads;
no warnings 'threads';

async {
    no warnings 'threads';
    sleep rand(10); ## One longe running process
    print 'Thread 2 finished first';
    exit;
};

sleep rand(10); ## another long running process
print 'thread 1 finished first';
exit;
[download]

The code will issue a warning A thread exited while 2 threads were running., but killing a thread this way is no worse that killing a process. From 5.8.8, no warnings 'threads'; is documented ... but not for this particular message it seems.