[ale] SIGALRM

[newcombe at aa.csc.peachnet.edu (Dan Newcombe)]

> Why would a program catch signal 14 (SIGALRM)?

They are quite the collectors item.  It fact, in SIGALRM issue number 
2, we learn that Superman was actually...well, never mind.

Alarm is similar to sleep.  Sleep puts the process to sleep for a 
certain amount of time.  While the timer counts down, the process can't 
do anything.

With Alarm, the process continues to run, and the timer counts down "in 
the background".  When the timer hits zero the system sends an SIGALRM 
to the process telling it the timer was done, and the process can then 
react.

An example:
	A process is expecting to read data from a (pipe|socket|device) 
within a certain amount of time.  If the process slept for that time,
it may miss some info.  By setting the alarm, the process can read 
whatever comes across while waiting for the alarm.  When the alarm 
happens, the process then knows that time is up, and should stop 
waiting for data (ie. it timed-out)

Hope this helps.
	-Dan

--
Dan Newcombe - Clayton State College - User Services - 770-961-3421 
newcombe at aa.csc.peachnet.edu  http://www.csc.peachnet.edu/home/dan/
-  Fearlessly the idiot faced the crowd - smiling.
                                    Pink Floyd, Fearless