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/ PBS::ProgressBar

NAME

PBS::ProgressBar - provide a progress meter on a standard terminal

SYNOPSIS

use PBS::ProgressBar;

$progress = PBS::ProgressBar->new ({count => $count});
$progress->update ($so_far);

DESCRIPTION

PBS::ProgressBar provides a simple progress bar on the terminal, to let the user know that something is happening, roughly how much stuff has been done, and maybe an estimate at how long remains.

A typical use sets up the progress bar with a number of items to do, and then calls update to update the bar whenever an item is processed.

Often, this would involve updating the progress bar many times with no user-visible change. To avoid uneccessary work, the update method returns a value, being the update value at which the user will next see a change. By only calling update when the current value exceeds the next update value, the call overhead is reduced.

Remember to call the $progress->update($max_value) when the job is done to get a nice 100% done bar.

A progress bar by default is simple; it just goes from left-to-right, filling the bar with '=' characters. These are called major characters. For long-running jobs, this may be too slow, so two additional features are available: a linear completion time estimator, and/or a minor character: this is a character that moves from left-to-right on the progress bar (it does not fill it as the major character does), traversing once for each major-character added. This exponentially increases the granularity of the bar for the same width.

EXAMPLES

A really simple use

#!/usr/bin/perl

use PBS::ProgressBar 2.00;

use constant MAX => 100_000;

my $progress = PBS::ProgressBar->new(MAX);

for (0..MAX) {
  my $is_power = 0;
  for(my $i = 0; 2**$i <= $_; $i++) {
    $is_power = 1
      if 2**$i == $_;
  }

  if ( $is_power ) {
    $progress->update($_);
  }
}

Here is a simple example. The process considers all the numbers between 0 and MAX, and updates the progress bar whenever it finds one. Note that the progress bar update will be very erratic. See below for a smoother example. Note also that the progress bar will never complete; see below to solve this.

The complete text of this example is in examples/powers in the distribution set (it is not installed as part of the module).

A smoother bar update

my $progress = PBS::ProgressBar->new($max);

for (0..$max) {
  my $is_power = 0;
  for(my $i = 0; 2**$i <= $_; $i++) {
    $is_power = 1
      if 2**$i == $_;
  }

  $progress->update($_)
}

This example calls update for each value considered. This will result in a much smoother progress update, but more program time is spent updating the bar than doing the "real" work. See below to remedy this. This example does not call $progress->update($max); at the end, since it is unnecessary, and ProgressBar will throw an exception at an attempt to update a finished bar.

The complete text of this example is in examples/powers2 in the distribution set (it is not installed as part of the module.

A (much) more efficient update

my $progress = PBS::ProgressBar->new({name => 'Powers', count => $max, remove => 1});
$progress->minor(0);
my $next_update = 0;

for (0..$max) {
  my $is_power = 0;
  for(my $i = 0; 2**$i <= $_; $i++) {
    $is_power = 1
      if 2**$i == $_;
  }

  $next_update = $progress->update($_)
    if $_ >= $next_update;
}
$progress->update($max)
  if $max >= $next_update;

This example does two things to improve efficiency: firstly, it uses the value returned by update to only call it again when needed; secondly, it switches off the use of minor characters to update a lot less frequently ($progress->minor(0);. The use of the return value of update means that the call of $progress->update($max); at the end is required to ensure that the bar ends on 100%, which gives the user a nice feeling.

This example also sets the name of the progress bar.

This example also demonstrates the use of the 'remove' flag, which removes the progress bar from the terminal when done.

The complete text of this example is in examples/powers3 in the distribution set (it is not installed as part of the module.

Using Completion Time Estimation

my $progress = PBS::ProgressBar->new({name  => 'Powers',
                                       count => $max,
                                       ETA   => linear, });
$progress->max_update_rate(1);
my $next_update = 0;

for (0..$max) {
  my $is_power = 0;
  for(my $i = 0; 2**$i <= $_; $i++) {
    if ( 2**$i == $_ ) {
      $is_power = 1;
      $progress->message(sprintf "Found %8d to be 2 ** %2d", $_, $i);
    }
  }

  $next_update = $progress->update($_)
    if $_ > $next_update;
}
$progress->update($max)
    if $max >= $next_update;

This example uses the ETA option to switch on completion estimation. Also, the update return is tuned to try to update the bar approximately once per second, with the max_update_rate call. See the documentation for the new method for details of the format(s) used.

This example also provides an example of the use of the message function to output messages to the same filehandle whilst keeping the progress bar intact

The complete text of this example is in examples/powers5 in the distribution set (it is not installed as part of the module.

CLASS CONSTANTS

INSTANCE CONSTRUCTION

new

Create & return a new PBS::ProgressBar instance.

ARGUMENTS

If one argument is provided, and it is a hashref, then the hash is treated as a set of key/value pairs, with the following keys; otherwise, it is treated as a number, being equivalent to the count key.

count

The item count. The progress is marked at 100% when update count is invoked, and proportionally until then.

name

A name to prefix the progress bar with.

fh

The filehandle to output to. Defaults to stderr. Do not try to use *foo{THING} syntax if you want Term capabilities; it does not work. Pass in a globref instead.

ETA

A total time estimation to use. If enabled, a time finished estimation is printed on the RHS (once sufficient updates have been performed to make such an estimation feasible). Naturally, this is an estimate; no guarantees are made. The format of the estimate

Note that the format is intended to be as compact as possible while giving over the relevant information. Depending upon the time remaining, the format is selected to provide some resolution whilst remaining compact. Since the time remaining decreases, the format typically changes over time.

As the ETA approaches, the format will state minutes & seconds left. This is identifiable by the word 'Left' at the RHS of the line. If the ETA is further away, then an estimate time of completion (rather than time left) is given, and is identifiable by 'ETA' at the LHS of the ETA box (on the right of the progress bar). A time or date may be presented; these are of the form of a 24 hour clock, e.g. '13:33', a time plus days (e.g., ' 7PM+3' for around in over 3 days time) or a day/date, e.g. ' 1Jan' or '27Feb'.

If ETA is switched on, the return value of update is also affected: the idea here is that if the progress bar seems to be moving quicker than the eye would normally care for (and thus a great deal of time is spent doing progress updates rather than "real" work), the next value is increased to slow it. The maximum rate aimed for is tunable via the max_update_rate component.

The available values for this are:

undef

Do not do estimation. The default.

linear

Perform linear estimation. This is simply that the amount of time between the creation of the progress bar and now is divided by the current amount done, and completion estimated linearly.

EXAMPLES
my $progress = PBS::ProgressBar->new(100); # count from 1 to 100
my $progress = PBS::ProgressBar->new({ count => 100 }); # same

# Count to 200 thingies, outputting to stdout instead of stderr,
# prefix bar with 'thingy'
my $progress = PBS::ProgressBar->new({ count => 200,
                                        fh    => \*STDOUT,
                                        name  => 'thingy' });

INSTANCE COMPONENTS

Scalar Components.

See "get_set" in Class::MethodMaker for usage.

target

The final target. Updates are measured in terms of this. Changes will have no effect until the next update, but the next update value should be relative to the new target. So

$p = PBS::ProgressBar({count => 20});
# Halfway
$p->update(10);
# Double scale
$p->target(40)
$p->update(21);

will cause the progress bar to update to 52.5%

max_update_rate

This value is taken as being the maximum speed between updates to aim for. It is only meaningful if ETA is switched on. It defaults to 0.5, being the number of seconds between updates.

Boolean Components

See "get_set" in Class::MethodMaker for usage.

minor

Default: set. If unset, no minor scale will be calculated or updated.

Minor characters are used on the progress bar to give the user the idea of progress even when there are so many more tasks than the terminal is wide that the granularity would be too great. By default, PBS::ProgressBar makes a guess as to when minor characters would be valuable. However, it may not always guess right, so this method may be called to force it one way or the other. Of course, the efficiency saving is minimal unless the client is utilizing the return value of update.

See examples/powers4 and examples/powers3 to see minor characters in action, and not in action, respectively.

INSTANCE HIGHER-LEVEL PROCEDURES

update

Update the progress bar.

ARGUMENTS
so_far

Current progress point, in whatever units were passed to new.

If not defined, assumed to be 1+ whatever was the value last time update was called (starting at 0).

RETURNS
next_call

The next value of so_far at which to call update.

message

Output a message. This is very much like print, but we try not to disturb the terminal.

ARGUMENTS
string

The message to output.

BUGS

REPORTING BUGS

Email the author.

COMPATIBILITY

If exactly two arguments are provided, then new operates in v1 compatibility mode: the arguments are considered to be name, and item count. Various other defaults are set to emulate version one (e.g., the major output character is '#', the bar width is set to 50 characters and the output filehandle is not treated as a terminal). This mode is deprecated.

AUTHOR

Martyn J. Pearce fluffy@cpan.org

Significant contributions from Ed Avis, amongst others.

COPYRIGHT

Copyright (c) 2001, 2002, 2003, 2004, 2005 Martyn J. Pearce. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

SEE ALSO