** Inter-process Communication **

HP unix is rich in methods for doing IPC. Some are only accessible via C.
Here's a very brief run down. For more details, see man pages or a
unix book like `Advanced Unix Programming' by Rochkind (there's a copy in
the dpo machine room).

1. Files
One process can write into a file then another can read it. This method
can be used in C and in shell scripts. Unique filenames can easily be

2. Pipes
Pipes can be created within C programs to connect related processes.

3. Named Pipes ( FIFOs)
These can be created from the command line using the mknod command
with the -p option.

4. Semaphores
A file's ontological status can be used as a semaphores between consenting
processes. System V also has C call's  to create and manage semaphores.
See ~tpl/doc/examples for a nearly working program.

5. Signals
Like interrupts. Only a few are available. Use kill in the shell or in
C programs. 

6 Shared Memory
Processes can both read and write to the same bit of memory. See the
C calls shget() , shmat() and ~tpl/doc/examples.

7. Sockets
A flexible bsd unix import. Processes can write to or listen at these.
An example program is in preparation.

   ipcs -b 
to see what semaphores, message queues and shared memory are being used.