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.\" ========================================================================
.\"
.IX Title "Net::Prometheus::Gauge 3pm"
.TH Net::Prometheus::Gauge 3pm "2020-11-09" "perl v5.32.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
"Net::Prometheus::Gauge" \- a snapshot value\-reporting metric
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&   use Net::Prometheus;
\&
\&   my $client = Net::Prometheus\->new;
\&
\&   my $gauge = $client\->new_gauge(
\&      name => "users",
\&      help => "Number of current users",
\&   );
\&
\&   my %users;
\&   ...
\&
\&   $gauge\->set( scalar keys %users );
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This class provides a gauge metric \- an arbitrary value that observes some
snapshot of state at some instant in time. This is often used to report on the
current usage of resources by the instrumented program, in a way that can
decrease as well as increase. It is a subclass of Net::Prometheus::Metric.
.SS "Value-Reporting Functions"
.IX Subsection "Value-Reporting Functions"
As an alternative to using the \f(CW\*(C`set\*(C'\fR method to update the value of the gauge,
a callback function can be used instead which should return the current value
to report for that gauge. This function is invoked at collection time, meaning
the reported value is up-to-date.
.PP
These functions are invoked inline as part of the collection process, so they
should be as small and lightweight as possible. Typical applications involve
reporting the size of an array or hash within the implementation's code.
.PP
.Vb 1
\&   $gauge\->set_function( sub { scalar @items } );
\&
\&   $gauge\->set_function( sub { scalar keys %things } );
.Ve
.SH "CONSTRUCTOR"
.IX Header "CONSTRUCTOR"
Instances of this class are not usually constructed directly, but instead via
the Net::Prometheus object that will serve it:
.PP
.Vb 1
\&   $gauge = $prometheus\->new_gauge( %args )
.Ve
.PP
This takes the same constructor arguments as documented in
Net::Prometheus::Metric.
.SH "METHODS"
.IX Header "METHODS"
.SS "set"
.IX Subsection "set"
.Vb 2
\&   $gauge\->set( @label_values, $value )
\&   $gauge\->set( \e%labels, $value )
\&
\&   $child\->set( $value )
.Ve
.PP
Sets the current value for the gauge.
.PP
If the gauge has any labels defined, the values for them must be given first.
.SS "set_function"
.IX Subsection "set_function"
.Vb 2
\&   $gauge\->set_function( @label_values, $func )
\&   $gauge\->set_function( \e%labels, $func )
\&
\&   $child\->set_function( $func )
.Ve
.PP
Sets a value-returning callback function for the gauge. If the gauge is
labeled, each label combination requires its own function.
.PP
When invoked, the function will be passed no arguments and is expected to
return a single value
.PP
.Vb 1
\&   $value = $func\->()
.Ve
.SS "inc"
.IX Subsection "inc"
.Vb 2
\&   $gauge\->inc( @label_values, $delta )
\&   $gauge\->inc( \e%labels, $delta )
\&
\&   $child\->inc( $delta )
.Ve
.PP
Increment the current value for the gauge. \f(CW$delta\fR will default to 1 if not
supplied.
.SS "dec"
.IX Subsection "dec"
.Vb 2
\&   $gauge\->dec( @label_values, $delta )
\&   $gauge\->dec( \e%labels, $delta )
\&
\&   $child\->dec( $delta )
.Ve
.PP
Decrement the current value for the gauge. \f(CW$delta\fR will default to 1 if not
supplied.
.SH "AUTHOR"
.IX Header "AUTHOR"
Paul Evans <leonerd@leonerd.org.uk>