Proc/NiceSleep version 0.57

STATUS
   This is BETA software.  The API is subject to change until 
   release 0.75, at which point it will be considered stable. 

   This module has been tested on linux, freebsd, and win32, and
   should work on any machine that runs perl. Comments, ideas, bug 
   reports, patches, and ports are greatly appreciated.

ABSTRACT
   Proc::NiceSleep is a Perl module which defines simple functions
   to allow a process to yield use of the system in an intelligent
   manner. See SYNOPSIS and DESCRIPTION below for details.

   The Proc::NiceSleep module is available on the Comprehensive Perl Archive 
   Network (CPAN). The latest version should always be available at 
   http://joshr.com/src/; http://cpan.perl.org/authors/id/J/JO/JOSHR/ 
   and mirrors may lag behind.

INSTALLATION
   To install this module type the following:

   perl Makefile.PL
   make
   make test
   make install

   or, if you use the CPAN shell, from the command line you can use:

   perl -MCPAN -e 'install Proc::NiceSleep'

DEPENDENCIES 
   This module requires no other non-standard perl modules, 
   but will perform with sub-second resolution only if Time::HiRes is 
   detected and supports it. For the load functions to have an effect, 
   Sys::CpuLoad must be found and successfully loaded.

NAME
    Proc::NiceSleep - yield system in an intelligent fashion

SYNOPSIS
      use Proc::NiceSleep qw( :all ); 
      nice(5);                  # lower our priority, if our OS supports it 
      max_load(1.1);            # max load we allow, if Sys::CpuLoad found
      sleep_factor(.5);         # sleep 50% as long as we run
      min_run_time(2);          # run at least 2 seconds without sleep
      while($somecondition) {
        #dosomething();
        $slept = maybe_sleep(); # sleep some amount of time if appropriate 
      }

  GETTING HELP
    If you have questions about Proc::NiceSleep, you can get help from the
    proc-nicesleep-at-joshr.com mailing list (replace -at- with @). You can
    subscribe to the list by sending the word 'subscribe' (no quotes) in the
    body of an email to

             proc-nicesleep-request-at-joshr.com

    There is also a Proc::NiceSleep announcement mailing list, to subscribe
    send an email with just the word 'subscribe' in the email to

             proc-nicesleep-announce-request-at-joshr.com

DESCRIPTION
    Proc::NiceSleep is a Perl module which defines subroutines to allow a
    process to yield use of the system in a method consistent with the
    configured policy. Proc::NiceSleep is intended for use in situations
    where the operating system does not support priorities, or where using
    the operating system's built-in priorities does not yield the system
    sufficiently.

    By default Proc::NiceSleep expects to yield the process for one tenth
    the amount of time that process runs. This is expressed by the default
    Sleep Factor of 0.10. Proc::NiceSleep can also be configured to attempt
    to keep the average system load below a certain threshhold through use
    of the max_load() function.

    A convenient nice() function, which acts much like the shell command and
    executable of the same name, is also provided for easy, platform
    independent access to your system's priorities (if available).

    If Proc::NiceSleep autodetects the presence of the Time::HiRes module
    (and your operating system supports it) then timing and yielding
    operations will occur with sub-second granularity. If not, no warning or
    error will be issued but Proc::NiceSleep operations will occur with a
    granularity of about one second. Sys::CpuLoad must be found for
    max_load() to have any effect.

    The following functions can be imported from this module.

    maybe_sleep ()
        Checks to see if this process should yield use of the system by
        issuing some kind of sleep at this point, and if so, does so for an
        appropriate amount of time. Returns 0 if no sleep was performed,
        otherwise returns the amount of seconds maybe_sleep() actually slept
        for.

    max_load ()
        Set or gets the maximum 1-minute average load allowed to occur
        before a sleep call will be issued by maybe_sleep(). The default
        value of 0 disables this feature; setting the maximum load will only
        have an effect if Sys::CpuLoad is successfully loaded. This module
        will check the system load no more than about once per second. If
        both sleep_factor() and max_load() are used then maybe_sleep() will
        yield the system if either condition is met.

    sleep_factor ()
        Sets or gets the sleep factor depending on whether a number is
        passed or not. A sleep factor of 1 means to sleep an equal amount of
        time as we run, 2 means to sleep twice as long, and so on. The
        default value is 0.1. If the sleep factor is set to zero, then this
        feature is disabled. If both sleep_factor() and max_load() are used
        then maybe_sleep() will yield the system if either condition is met.

    nice ()
        Sets or gets the priority of the process, as understood by the
        operating system. If passed an integer, nice() attempts to set
        priority of the process to the value specified, and returns that
        value. If no parameter is passed, nice() attempts to query the
        operating system for the priority of the process and return it. If
        your OS doesn't support priorities then nice() will likely always
        return 0.

        The exact nice() values returned and recognized, and their meanings
        to the system, are system dependent but usually range from about -20
        (highest priority) to 20 (lowest priority, 'nicest').

    min_run_time ()
        Sets or gets the minimum run time, in seconds, depending on whether
        a number is passed or not. The minumum run time is the least amount
        of time that Proc::NiceSleep will allow the process to run between
        sleeps. The default value is 0.01 seconds.

    min_sleep_time ()
        Sets or gets the minimum amount time, in seconds, that maybe_sleep()
        will sleep for if it detects that a sleep is appropriate. Setting
        the minimum sleep time to zero (which is also the default value)
        will disable this feature.

    DumpText ()
        Returns a string (intended for display) containing multiple lines
        with internal information about Proc::NiceSleep's runtime
        configuration and statistics. The format and contents of the
        returned string are intended for informational and debugging use and
        are subject to change.

    Dump ()
        Returns a reference to a hash with internal information about
        Proc::NiceSleep configuration and statistics. The names and presence
        of the returned hash names and values are for informational and
        debugging purposes only and are subject to change. Modifying the
        returned hash will have no effect on the operation of
        Proc::NiceSleep.

EXPORT
    None by default.

AUTHOR
    Josh Rabinowitz, <joshr-proc-nicesleep@joshr.com>

CAVEATS
    The meanings of values accepted by nice() may vary between operating
    systems (e.g. HP-UX). This problem is to be addressed in future
    revisions to this package; for now be advised that use of nice() is not
    necessarily portable.

    Uncoordinated use of sleep() (and possibly of signal() and alarm()) in
    your perl program may cause your program to yield the system more or
    less than specified via Proc::NiceSleep policies.

SEE ALSO
    Time::HiRes, Sys::CpuLoad

COPYRIGHT
    Copyright (c) 2002 Josh Rabinowitz. All rights reserved. This program is
    free software; you can redistribute it and/or modify it under the same
    terms as Perl itself.

ACKNOWLEDGEMENTS
    Proc::NiceSleep is loosely modeled on Lincoln Stein's CGI.pm, and on D.
    Wegscheid and other's Time::HiRes.pm. Thanks to Michael G Schwern,
    Terrence Brannon, and David Alban for their valuable input.

