Semaphores and/or Shared Memory Implementations for 4.2BSD

[Don Libes]

I wrote a system for shared variables for 4.2.  Briefly:

A common memory server takes requests from client processes to declare,
read or write variables.  Common memory, then, is storage local to the CM
server.  Variables are typed, along with some other attributes such as
protection, lifetime, etc.  The manager can be told to wake up a process
if a variable has changed.  Thats the general idea.

For the way we're using it, semaphores aren't necessary (but they
would be easy to add).  One call, cm_sync(), updates the user's idea
of common memory variables with the manager's.  Its noninterruptible,
since the manager completely processes requests in the order they are
received.

In case its not obvious, this is all user level code.  

Don Libes	seismo!nbs-amrf!libes