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.

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