Library: Prometheus
Package: Core
Header: Poco/Prometheus/CallbackMetric.h
Description
A generic Metric implementation where the sample is obtained via a callback function or lambda.
The callback is invoked whenever the value of the metric is requested. This is typically when the metric is written to an Exporter.
This is implemented as a template to support both counter and gauge metrics with different underlying types.
Note that only metric types COUNTER and GAUGE are supported.
Labels are not supported.
Example usage:
CallbackMetric<Poco::UInt64, Metric::Type::COUNTER> sampleCount(
"sample_count"s,
[]()
{
return 42;
}
);
There are also pre-instantiated types available:
The following sample types are supported:
Inheritance
Direct Base Classes: Metric
All Base Classes: Collector, Metric
Member Summary
Member Functions: exportTo, help, value
Inherited Functions: exportTo, help, name, setHelp, type, validateName
Types Aliases
Callback
using Callback = std::function < Sample ()>;
Sample
using Sample = T;
Constructors
CallbackMetric 
CallbackMetric(
const std::string & name,
Callback callback
);
Creates a CallbackMetric with the given type and name and registers it with the default registry.
CallbackMetric
CallbackMetric(
const std::string & name,
const std::string & help,
Callback callback
);
Creates a CallbackMetric with the given type, name and help text, and registers it with the default registry.
CallbackMetric
CallbackMetric(
const std::string & name,
Registry * pRegistry,
Callback callback
);
Creates a CallbackMetric with the given type and name and registers it with the given registry (if not nullptr).
CallbackMetric
CallbackMetric(
const std::string & name,
const std::string & help,
Registry * pRegistry,
Callback callback
);
Creates a CallbackMetric with the given type, name and help text, and registers it with the given registry (if not nullptr).
Destructor
~CallbackMetric 
~CallbackMetric() = default;
Destroys the CallbackMetric.
Member Functions
exportTo
void exportTo(
Exporter & exporter
) const override;
See also: Poco::Prometheus::Collector::exportTo()
help
CallbackMetric & help(
const std::string & text
);
Sets the CallbackMetric's help text.
Must only be set once, immediately after creating the CallbackMetric.
value
Sample value() const;
Invokes the callback function and returns the value returned by it.