term% ls -F
term% cat index.txt
RENDEZVOUS(2)                 System Calls Manual                RENDEZVOUS(2)

       rendezvous - user level process synchronization

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

       ulong rendezvous(ulong tag, ulong value)

       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.


       segattach(2), fork(2)

       Sets errstr.

       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.