RENDEZVOUS(2) 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 synchro-
nize 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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