05-04-2014
Quote:
Originally Posted by
sidharthmellam
my concern is , why the sleeping process is consuming resources ,
It might help to understand what a "sleeping" process is, so here it goes:
Suppose a process starts: it gets loaded into memory, so some memory has to be allocated to it. It also gets some processor time, otherwise it would lurk just there, unable to run. Now it starts and probably it will need some additional memory to hold runtime data, it might need other OS resources, like files to be opened, network connections to be established, etc., etc..
All these requests involve the OS, which may or may not be able to fulfill these immediately. If it is, the process gets what it requests, but if not it will be put to sleep until the OS can provide. That it is put to sleep does not mean it has nothing to do or that it could be stopped. This is just a way for the OS to do something else until it can provide everything necessary to run the process.
Another possiblity is that the process waits for a certain event: suppose the process services a certain network event: it will listen to the network and until a certain signal comes it has nothing to do - therefore it is going to sleep. When the signal comes, it wakes up, does whatever it is supposed to do, then goes back to sleep again. If you stop the process because it sleeps it will not be able to wake up once the signal comes.
I hope this helps.
bakunin
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SLEEP(3) BSD Library Functions Manual SLEEP(3)
NAME
sleep -- suspend thread execution for an interval measured in seconds
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <unistd.h>
unsigned int
sleep(unsigned int seconds);
DESCRIPTION
The sleep() function suspends execution of the calling thread until either seconds seconds have elapsed or a signal is delivered to the
thread and its action is to invoke a signal-catching function or to terminate the thread or process. System activity may lengthen the sleep
by an indeterminate amount.
This function is implemented using nanosleep(2) by pausing for seconds seconds or until a signal occurs. Consequently, in this implementa-
tion, sleeping has no effect on the state of process timers, and there is no special handling for SIGALRM.
RETURN VALUES
If the sleep() function returns because the requested time has elapsed, the value returned will be zero. If the sleep() function returns due
to the delivery of a signal, the value returned will be the unslept amount (the requested time minus the time actually slept) in seconds.
SEE ALSO
nanosleep(2), usleep(3)
STANDARDS
The sleep() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1'').
HISTORY
A sleep() function appeared in Version 7 AT&T UNIX.
BSD
February 13, 1998 BSD