term% cat index.txt 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 ex‐
change 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 ex‐
changed between the processes and returned as the result of the respec‐
tive 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 un‐
less they need to share the name space with their parent. This is es‐
pecially important in Alef programs.
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