120 lines
5.2 KiB
Go
120 lines
5.2 KiB
Go
// Copyright 2014 The Prometheus Authors
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package prometheus
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// Collector is the interface implemented by anything that can be used by
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// Prometheus to collect metrics. A Collector has to be registered for
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// collection. See Registerer.Register.
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//
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// The stock metrics provided by this package (Gauge, Counter, Summary,
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// Histogram, Untyped) are also Collectors (which only ever collect one metric,
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// namely itself). An implementer of Collector may, however, collect multiple
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// metrics in a coordinated fashion and/or create metrics on the fly. Examples
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// for collectors already implemented in this library are the metric vectors
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// (i.e. collection of multiple instances of the same Metric but with different
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// label values) like GaugeVec or SummaryVec, and the ExpvarCollector.
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type Collector interface {
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// Describe sends the super-set of all possible descriptors of metrics
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// collected by this Collector to the provided channel and returns once
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// the last descriptor has been sent. The sent descriptors fulfill the
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// consistency and uniqueness requirements described in the Desc
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// documentation.
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//
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// It is valid if one and the same Collector sends duplicate
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// descriptors. Those duplicates are simply ignored. However, two
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// different Collectors must not send duplicate descriptors.
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//
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// Sending no descriptor at all marks the Collector as “unchecked”,
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// i.e. no checks will be performed at registration time, and the
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// Collector may yield any Metric it sees fit in its Collect method.
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//
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// This method idempotently sends the same descriptors throughout the
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// lifetime of the Collector. It may be called concurrently and
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// therefore must be implemented in a concurrency safe way.
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//
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// If a Collector encounters an error while executing this method, it
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// must send an invalid descriptor (created with NewInvalidDesc) to
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// signal the error to the registry.
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Describe(chan<- *Desc)
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// Collect is called by the Prometheus registry when collecting
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// metrics. The implementation sends each collected metric via the
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// provided channel and returns once the last metric has been sent. The
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// descriptor of each sent metric is one of those returned by Describe
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// (unless the Collector is unchecked, see above). Returned metrics that
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// share the same descriptor must differ in their variable label
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// values.
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//
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// This method may be called concurrently and must therefore be
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// implemented in a concurrency safe way. Blocking occurs at the expense
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// of total performance of rendering all registered metrics. Ideally,
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// Collector implementations support concurrent readers.
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Collect(chan<- Metric)
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}
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// DescribeByCollect is a helper to implement the Describe method of a custom
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// Collector. It collects the metrics from the provided Collector and sends
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// their descriptors to the provided channel.
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//
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// If a Collector collects the same metrics throughout its lifetime, its
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// Describe method can simply be implemented as:
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//
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// func (c customCollector) Describe(ch chan<- *Desc) {
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// DescribeByCollect(c, ch)
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// }
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//
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// However, this will not work if the metrics collected change dynamically over
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// the lifetime of the Collector in a way that their combined set of descriptors
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// changes as well. The shortcut implementation will then violate the contract
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// of the Describe method. If a Collector sometimes collects no metrics at all
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// (for example vectors like CounterVec, GaugeVec, etc., which only collect
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// metrics after a metric with a fully specified label set has been accessed),
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// it might even get registered as an unchecked Collector (cf. the Register
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// method of the Registerer interface). Hence, only use this shortcut
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// implementation of Describe if you are certain to fulfill the contract.
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//
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// The Collector example demonstrates a use of DescribeByCollect.
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func DescribeByCollect(c Collector, descs chan<- *Desc) {
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metrics := make(chan Metric)
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go func() {
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c.Collect(metrics)
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close(metrics)
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}()
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for m := range metrics {
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descs <- m.Desc()
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}
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}
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// selfCollector implements Collector for a single Metric so that the Metric
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// collects itself. Add it as an anonymous field to a struct that implements
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// Metric, and call init with the Metric itself as an argument.
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type selfCollector struct {
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self Metric
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}
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// init provides the selfCollector with a reference to the metric it is supposed
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// to collect. It is usually called within the factory function to create a
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// metric. See example.
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func (c *selfCollector) init(self Metric) {
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c.self = self
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}
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// Describe implements Collector.
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func (c *selfCollector) Describe(ch chan<- *Desc) {
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ch <- c.self.Desc()
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}
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// Collect implements Collector.
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func (c *selfCollector) Collect(ch chan<- Metric) {
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ch <- c.self
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}
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