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Full Discussion: fork() in for loop
Top Forums Programming fork() in for loop Post 25980 by Perderabo on Thursday 8th of August 2002 01:09:26 PM
Old 08-08-2002
fork() makes a copy of a process. If you do that in a "for" loop, you have a problem. The first time through the loop you invoke fork() and now you have two processes. Unless you have code to prevent it, both processes with continue to run that loop. On the second iteration you get 4 processes, then 8, then 16, then 32.... Anr 32 processes all forking themselves will put a nasty load on the system.
 

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LEARN ABOUT PLAN9

rendezvous

RENDEZVOUS(2)							System Calls Manual						     RENDEZVOUS(2)

NAME

       rendezvous - user level process synchronization

SYNOPSIS

       #include <u.h>
       #include <libc.h>

       ulong rendezvous(ulong tag, ulong value)

DESCRIPTION

       The  rendezvous	system	call allows two processes to synchronize and exchange a value.	In conjunction with the shared memory system calls
       (see segattach(2) and fork(2)), it enables parallel programs to control their scheduling.

       Two processes wishing to synchronize call rendezvous with a common tag, typically an address in memory they share.  One process will arrive
       at  the rendezvous first; it suspends execution until a second arrives.	When a second process meets the rendezvous the value arguments are
       exchanged between the processes and returned as the result of the respective rendezvous system calls.  Both processes are awakened when the
       rendezvous succeeds.

       The tag space is common to processes in the same file name space, so rendezvous only works between processes in the same file name space.

       If a rendezvous is interrupted the return value is ~0, so that value should not be used in normal communication.

SOURCE

       /sys/src/libc/9syscall

SEE ALSO

       segattach(2), fork(2)

DIAGNOSTICS

       Sets errstr.

BUGS

       The  correlation of rendezvous tags and file name space is a historical accident.  If two unrelated processes happen to be in the same name
       space and do a rendezvous, trouble will result.	The solution is to call rfork(RFNAMEG) (see  fork(2))  in  programs  that  use	rendezvous
       unless they need to share the name space with their parent.  This is especially important in Alef programs.

																     RENDEZVOUS(2)
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