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