PERLIPC

Man Page for PERLIPC


NAME
     perlipc - Perl interprocess communication

DESCRIPTION
     The IPC facilities of Perl are built on the Berkeley socket
     mechanism.  If you don't have sockets, you can ignore this
     section.  The calls have the same names as the corresponding
     system calls, but the arguments tend to differ, for two
     reasons.  First, Perl file handles work differently than C
     file descriptors.  Second, Perl already knows the length of
     its strings, so you don't need to pass that information.

     Client/Server Communication

     Here's a sample TCP client.

         ($them,$port) = @ARGV;
         $port = 2345 unless $port;
         $them = 'localhost' unless $them;

         $SIG{'INT'} = 'dokill';
         sub dokill { kill 9,$child if $child; }

         use Socket;

         $sockaddr = 'S n a4 x8';
         chop($hostname = `hostname`);

         ($name, $aliases, $proto) = getprotobyname('tcp');
         ($name, $aliases, $port) = getservbyname($port, 'tcp')
             unless $port =~ /^+$/;
         ($name, $aliases, $type, $len, $thisaddr) =
                         gethostbyname($hostname);
         ($name,  $aliases,  $type, $len, $thataddr) = gethostby-
name($them);

         $this = pack($sockaddr, &AF_INET, 0, $thisaddr);
         $that = pack($sockaddr, &AF_INET, $port, $thataddr);

         socket(S,  &PF_INET,  &SOCK_STREAM,   $proto)   ||   die
"socket: $!";
         bind(S, $this) || die "bind: $!";
         connect(S, $that) || die "connect: $!";

         select(S); $| = 1; select(stdout);











         if ($child = fork) {
             while (<>) {
                 print S;
             }
             sleep 3;
             do dokill();
         }
         else {
             while (<S>) {
                 print;
             }
         }

     And here's a server:

         ($port) = @ARGV;
         $port = 2345 unless $port;

         use Socket;

         $sockaddr = 'S n a4 x8';

         ($name, $aliases, $proto) = getprotobyname('tcp');
         ($name, $aliases, $port) = getservbyname($port, 'tcp')
             unless $port =~ /^+$/;

         $this = pack($sockaddr, &AF_INET, $port, "    ");

         select(NS); $| = 1; select(stdout);

         socket(S,   &PF_INET,   &SOCK_STREAM,   $proto)  ||  die
"socket: $!";
         bind(S, $this) || die "bind: $!";
         listen(S, 5) || die "connect: $!";

         select(S); $| = 1; select(stdout);

         for (;;) {
             print "Listening again0;
             ($addr = accept(NS,S)) || die $!;
             print "accept ok0;

             ($af,$port,$inetaddr) = unpack($sockaddr,$addr);
             @inetaddr = unpack('C4',$inetaddr);
             print "$af $port @inetaddr0;

             while (<NS>) {
                 print;
                 print NS;
             }
         }

PERLIPC(1)               USER COMMANDS  Release 5.0 Patchlevel 00



     SysV IPC

     Here's a small example showing shared memory usage:

         $IPC_PRIVATE = 0;
         $IPC_RMID = 0;
         $size = 2000;
         $key = shmget($IPC_PRIVATE, $size , 0777 );
         die if !defined($key);

         $message = "Message #1";
         shmwrite($key, $message, 0, 60 ) || die "$!";
         shmread($key,$buff,0,60) || die "$!";

         print $buff,"0;

         print "deleting $key0;
         shmctl($key ,$IPC_RMID, 0) || die "$!";

     Here's an example of a semaphore:

         $IPC_KEY = 1234;
         $IPC_RMID = 0;
         $IPC_CREATE = 0001000;
         $key = semget($IPC_KEY, $nsems , 0666 | $IPC_CREATE );
         die if !defined($key);
         print "$key0;

     Put this code in a separate file to be run in more that one
     process Call the file take:

         # create a semaphore

         $IPC_KEY = 1234;
         $key = semget($IPC_KEY,  0 , 0 );
         die if !defined($key);

         $semnum = 0;
         $semflag = 0;

         # 'take' semaphore
         # wait for semaphore to be zero
         $semop = 0;
         $opstring1 = pack("sss", $semnum, $semop, $semflag);

         # Increment the semaphore count
         $semop = 1;
         $opstring2 = pack("sss", $semnum, $semop,  $semflag);
         $opstring = $opstring1 . $opstring2;

	 semop($key,$opstring) || die "$!";

     Put this code in a separate file to be run in more that one
     process Call this file give:

         #'give' the semaphore
         # run this in the original process and you will see
         # that the second process continues

         $IPC_KEY = 1234;
         $key = semget($IPC_KEY, 0, 0);
         die if !defined($key);

         $semnum = 0;
         $semflag = 0;

         # Decrement the semaphore count
         $semop = -1;
         $opstring = pack("sss", $semnum, $semop, $semflag);

         semop($key,$opstring) || die "$!";
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