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Forking in Perl, then communicating between processes
Interprocess Communication example from a Well House Consultants training course
More on Interprocess Communication [link]
Source code: fdem Module: P223
=head1 Forking in Perl The fork function in Perl splits the current process into two, duplicating all variables into each of the new processes. One of the new processes is known as the "parent" - this is the original process (under the original process id), and the other is know as the "child", which has a new process id. You can tell them apart by checking the value returned by fork - in the child it returns a zero, but in the parent it returns the process id of the newly created child. Based on the returned value, the parent and the child can go off to perform different tasks. You should take care in your code, though, to ensure that you add an exit call if appropriate to avoid one dropping through into the other at run time. Parent and child can alert each other via signals (not illustrated in this simple example) or writing messages to and from each other via a pipe. If you open a pipe before you fork, with two file handles, you can then (after forking) write to one of the file handles in the parent and read in the child, and / or write to a file handle in the child and read at the parent. This use of pipes to communicate between processes allows the processes to wait for one another (syncronise) when each of their individual tasks reaches a strategic point. =cut print "hello\n"; $abc = 123; $ppid = $$; pipe(FHX, FHY); if (!($pid = fork())) { print ("$abc ... Child of $ppid is $$\n"); sleep 5; print "yawn\n"; sleep 5; print "yawn\n"; print FHY ("OK, Mum, I'm done\n"); print "Child completed\n"; exit; } print ("$abc ... Parent is $ppid with child $pid\n"); sleep 4; print "yeah\n"; sleep 4; print "yeah\n"; $woch = <FHX>; print ("Always sitting at the school gate!\n"); print $woch; __END__ Dorothy:csr1 grahamellis$ perl fdem hello 123 ... Parent is 414 with child 415 123 ... Child of 414 is 415 yeah yawn yeah yawn Child completed Always sitting at the school gate! OK, Mum, I'm done Dorothy:csr1 grahamellis$ Learn about this subject
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This example comes from our "Interprocess Communication" training module. You'll find a description of the topic and some
other closely related examples on the "Interprocess Communication" module index page.
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