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Top Forums UNIX for Dummies Questions & Answers timer interrupt Post 302077022 by Perderabo on Sunday 18th of June 2006 07:59:39 PM
Old 06-18-2006
Sometimes a process needs something that is not available....a free disk buffer, some data from disk, or maybe just a signal. So it will go to sleep and wait for the resource to become available. This act of sleeping on a resource is what raises a process' priority to a kernel priority. But a sleeping process is not using a cpu. When the resource becomes available, the process will run at the elevated level, but, if the kernel is well written, this will be a very short time. Either it will sleep for something else or it will return to user mode. At return to user mode time, the priority is recalculated. Since the process recently spent time asleep, it will get credit for not hogging the cpu.

Thus very high priority processes tend to not be running and do not want the cpu. The quantum is based on cpu time, not elapsed time. But if the quantum were to be consumed while the process is in system mode, this will be detected upon the return to user mode.

But no matter how high the priority is, if another higher priority wants the cpu, the lower priority process will be preempted. You are getting confused with another issue. Unix guarantees that some system calls are atomic. To meet this guarantee, it has a concept of very high priority. The difference is a that a very high priority process will not wake up if a signal is sent to it. The signal will be pending until its priority lowers somewhat. If a process is writing to a disk file, it will not be signalable until the write completes. But if a process is writing to a tty, a signal can interrupt the write before it completes.
 

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Xacobeo::Timer(3pm)					User Contributed Perl Documentation				       Xacobeo::Timer(3pm)

NAME
Xacobeo::Timer - A custom made timer. SYNOPSIS
use Xacobeo::Timer; # As a one time use my $timer = Xacobeo::Timer->start("Long operation"); do_long_operation(); $timer->elapsed(); # Displays the time elapsed # A simple stop watch (the destructor displays the time elapsed) my $TIMER = Xacobeo::Timer->new("Method calls"); sub hotspot { $TIMER->start(); # Very slow stuff here $TIMER->stop(); } DESCRIPTION
This package provides a very simple timer. This timer is used for finding hot spots in the application. The timer is quite simple it provides the method "start" that starts the timer and the method "stop" that stops the timer and accumulates the elapsed time. The method "show" can be used to print the time elapsed so far while the method "elapsed" returns the time elapsed so far. When an instance of this class dies (because it was undefed or collected by the garbage collector) the builtin Perl desctrutor will automatically call the method "show". But if the method show or elapsed was called during the lifetime of the instance then the destructor will not invoke the method show. METHODS
The package defines the following methods: new Creates a new Timer. Parameters: o $name (Optional) The name of the timer. start Starts the timer. If this sub is called without a blessed instance then a new Timer will be created. Parameters: o $name (optional) The name is used only when called without a blessed instance. stop Stops the timer and adds accumulates the elapsed time. If the timer wasn't started previously this results in a no-op. show Prints the elapsed time. This method stops the timer if it was started previously and wasn't stopped. elapsed Returns the total time elapsed so far. If the timer was already started the pending time will not be taking into account. AUTHORS
Emmanuel Rodriguez <potyl@cpan.org>. COPYRIGHT AND LICENSE
Copyright (C) 2008,2009 by Emmanuel Rodriguez. This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.8 or, at your option, any later version of Perl 5 you may have available. perl v5.14.2 2011-11-16 Xacobeo::Timer(3pm)
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