G'day wonderG,

Welcome to the Monastery.

"The above if block if(wait() == -1) can not be executed..."

The short answer is because "wait() == -1" is FALSE.

"...could you help to check if there is any errors in my code"

You've presented us with incomplete code. This just raises a lot of questions and means we have to engage in guesswork if we were to attempt an answer.

Please cut down your code to a minimum, that we can run, and reproduces the problem; as described in "Short, Self-Contained, Correct Example". Also, follow the guidelines in "How do I post a question effectively?".

It would also be preferable unless you do use potentially confusing constructs like "unless (...) {...} else {...}". Confused? Try s/unless you do/if you don't/. :-)

Here's some very basic code that uses wait() and doesn't have a problem. 

#!/usr/bin/env perl

use strict;
use warnings;

my $pid = fork();

if (defined $pid) {
    if ($pid) {
        print "Parent: $$; Child: $pid\n";
        my $wait = wait();
        print "Parent waited on Child: $wait\n";
    }
    else {
        print "Child: $$\n";
        exit;
    }
}
else {
    warn 'Fork failed!';
}

[download]

Sample output:

Parent: 553; Child: 554
Child: 554
Parent waited on Child: 554

[download]

This may highlight your problem and allow you to fix it. If not, add small amounts of code until your problem resurfaces; then post that and ask for our help.

See also waitpid().

— Ken

In reply to Re: Multiprocess - child process cannot be finished successfully by kcott
in thread Multiprocess - child process cannot be finished successfully by wonderG

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