LECTURE 3, WED FEB 2

**Pipes, for inter-process communication.

Unnamed pipe betw parent and child.

2-element integer array as pipe ptr object; pipe() API call.

demo of simple pipe.c sample code, with child writing to parent.

do you need to close the read end if you're only writing?  apparently
not on Alpha linux.

how are pipes implemented?  FIFO (unlike stacks, which are LIFO),
using files.  unnamed pipe is built on an invisible file that only the
OS knows about.

what is diff between pwrite/pread and write/read?  we are not sure.


**Signals, which the OS sends to your process

signals are software interrupts, generated by the operating system

there are multiple APIs for setting up signals

demo of catch-ctrl-c.c

sending signals to processes via the shell using the 'kill' cmd

there are multiple signals with numeric ids

you can't trap the SIGKILL signal

demo of periodic signalling using 'alarm'; ticktock.c code.