anshumangoyal has asked for the wisdom of the Perl Monks concerning the following question:

I have a code where I send command to another machine and wait for it's response over UDP. Now, I want when the response from remote machine stops coming for 'time-out' number of seconds i should close the socket and come out. Here is the code/function i am using. Problem is alarm is not triggered and the program remains in infinite loop. Can any one help. 
sub ReceiveResponse {
    my $port = shift;
    my $time_out = 1;
    
    print "FW Machine: Waiting for Command Response On Port $recv_port
+\n";
    
    eval {
        local $SIG{ALRM} = sub { 
            die "Timed Out";
        };
        my $socket_resp = IO::Socket::INET->new(LocalPort => $recv_por
+t, Proto => 'udp', Timeout => undef);
        alarm 10;
        while (1) {
            my $recieved_data;
            $socket_resp->recv($recieved_data,1024);
            my $peer_address = $socket_resp->peerhost();
            my $peer_port = $socket_resp->peerport();
            if ($peer_address eq $send_ip_address) {
                my $desti = GetIP();
                chomp($recieved_data);
                print "$peer_address:$peer_port > $desti:$recv_port =>
+ $recieved_data\n";
                if ($recieved_data =~ m/^done/i) {
                    last;
                }
            }
        }
        
        $socket_resp->close();
        alarm 0;
    };

    alarm 0;
    
    if ($@ =~ /Timed Out/i) {
        print "Timed-Out Receiving Data from UDP\n";
    }
}

[download]

Replies are listed 'Best First'.
Re: alarm not working
by aitap (Curate) on Jul 11, 2012 at 09:19 UTC
    The following code works normally: 
    #!/usr/bin/perl

eval {
        local $SIG{ALRM} = sub { 
            die "Timed Out";
        };
        alarm 3;
        sleep 1 while 1;
        
        alarm 0;
};

alarm 0;
    
if ($@ =~ /Timed Out/i) {
    print "Timed-Out waiting for infinite loop to finish\n";
}

    [download]
    So I guess, your problem is that $socket_resp->recv($recieved_data,1024); blocks until it receives 1024 bytes. Try adding Blocking => 0 to IO::Socket::INET->new() arguments. You would also probably want to substitute my $port = shift; with my $recv_port = shift; (use warnings; warned about it).
    Sorry if my advice was wrong.
[reply]
[d/l]
[select]
      Blocking does not resolve the problem. Here is the code, I am still facing the issue the program is not killed after alarm but sits back waiting and waiting. 
          my $socket_resp = IO::Socket::INET->new(LocalPort => $response_por
+t, Proto => 'udp', Blocking => 1, Timeout => undef);
    
    print "FW Machine: Waiting for Command Response On Port $response_
+port\n";
    
    eval {
        local $SIG{ALRM} = sub { 
            die "Timed Out";
        };
        alarm 10;

        while (1) {
            my $recieved_data;
            $socket_resp->recv($recieved_data, 1024);
            alarm 10;
            my $peer_address = $socket_resp->peerhost();
            my $peer_port = $socket_resp->peerport();
            if ($peer_address eq $send_ip_address) {
                my $desti = GetIP();
                chomp($recieved_data);
                print "$peer_address:$peer_port > $desti:$response_por
+t => $recieved_data\n";
                if ($recieved_data =~ m/^done/i) {
                    last;
                }
            }
        }
        
        alarm 0;
    };
    
    alarm 0;
    
    if ($@ =~ /Timed Out/i) {
        print "Timed-Out waiting for infinite loop to finish\n";
    }
    
    $socket_resp->close();

      [download]
[reply]
[d/l]

        alarm() on Windows cannot interrupt system calls, so there should be another answer.(see Alphabetical Listing of Perl Functions)

        Can you try the third method from Re: what does timeout mean in IO::Socket::INET ?? It seems to be the right thing.

        Also, I may have misunderstood somethng, but Blocking is set to 1 in your code. If all else fails, the following (ugly) kludge can help: 

        my $socket_resp = IO::Socket::INET->new(LocalPort => $response_port, P
+roto => 'udp', Blocking => 0, Timeout => undef);
...
$received_data=&timeout_recv($socket,1024,10);
...
sub timeout_recv {
 my $return;
 my $buf;
 my $cnt=0;
 for (1..$_[2]) { # $_[2] is timeout
  $_[0]->recv($buf,$_[1]-$cnt) // 0; # $_[1] is count of bytes to rece
+ive
  $cnt += length $buf;
  $return .= $buf;
  return $return if $cnt == $_[1];
  sleep 1; # the ugliest line
 }
 die "Timed Out";
}

        [download]

        Sorry if my advice was wrong.
[reply]
[d/l]
[select]
Re: alarm not working
by BrowserUk (Patriarch) on Jul 11, 2012 at 09:28 UTC

    What OS are you on?

[reply]
      I am on Windows OS.
[reply]

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