khenaidoo | ffe076b | 2019-01-15 16:08:08 -0500 | [diff] [blame^] | 1 | // Copyright 2014 The Prometheus Authors |
| 2 | // Licensed under the Apache License, Version 2.0 (the "License"); |
| 3 | // you may not use this file except in compliance with the License. |
| 4 | // You may obtain a copy of the License at |
| 5 | // |
| 6 | // http://www.apache.org/licenses/LICENSE-2.0 |
| 7 | // |
| 8 | // Unless required by applicable law or agreed to in writing, software |
| 9 | // distributed under the License is distributed on an "AS IS" BASIS, |
| 10 | // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 11 | // See the License for the specific language governing permissions and |
| 12 | // limitations under the License. |
| 13 | |
| 14 | package prometheus |
| 15 | |
| 16 | // Collector is the interface implemented by anything that can be used by |
| 17 | // Prometheus to collect metrics. A Collector has to be registered for |
| 18 | // collection. See Registerer.Register. |
| 19 | // |
| 20 | // The stock metrics provided by this package (Gauge, Counter, Summary, |
| 21 | // Histogram, Untyped) are also Collectors (which only ever collect one metric, |
| 22 | // namely itself). An implementer of Collector may, however, collect multiple |
| 23 | // metrics in a coordinated fashion and/or create metrics on the fly. Examples |
| 24 | // for collectors already implemented in this library are the metric vectors |
| 25 | // (i.e. collection of multiple instances of the same Metric but with different |
| 26 | // label values) like GaugeVec or SummaryVec, and the ExpvarCollector. |
| 27 | type Collector interface { |
| 28 | // Describe sends the super-set of all possible descriptors of metrics |
| 29 | // collected by this Collector to the provided channel and returns once |
| 30 | // the last descriptor has been sent. The sent descriptors fulfill the |
| 31 | // consistency and uniqueness requirements described in the Desc |
| 32 | // documentation. |
| 33 | // |
| 34 | // It is valid if one and the same Collector sends duplicate |
| 35 | // descriptors. Those duplicates are simply ignored. However, two |
| 36 | // different Collectors must not send duplicate descriptors. |
| 37 | // |
| 38 | // Sending no descriptor at all marks the Collector as “unchecked”, |
| 39 | // i.e. no checks will be performed at registration time, and the |
| 40 | // Collector may yield any Metric it sees fit in its Collect method. |
| 41 | // |
| 42 | // This method idempotently sends the same descriptors throughout the |
| 43 | // lifetime of the Collector. It may be called concurrently and |
| 44 | // therefore must be implemented in a concurrency safe way. |
| 45 | // |
| 46 | // If a Collector encounters an error while executing this method, it |
| 47 | // must send an invalid descriptor (created with NewInvalidDesc) to |
| 48 | // signal the error to the registry. |
| 49 | Describe(chan<- *Desc) |
| 50 | // Collect is called by the Prometheus registry when collecting |
| 51 | // metrics. The implementation sends each collected metric via the |
| 52 | // provided channel and returns once the last metric has been sent. The |
| 53 | // descriptor of each sent metric is one of those returned by Describe |
| 54 | // (unless the Collector is unchecked, see above). Returned metrics that |
| 55 | // share the same descriptor must differ in their variable label |
| 56 | // values. |
| 57 | // |
| 58 | // This method may be called concurrently and must therefore be |
| 59 | // implemented in a concurrency safe way. Blocking occurs at the expense |
| 60 | // of total performance of rendering all registered metrics. Ideally, |
| 61 | // Collector implementations support concurrent readers. |
| 62 | Collect(chan<- Metric) |
| 63 | } |
| 64 | |
| 65 | // DescribeByCollect is a helper to implement the Describe method of a custom |
| 66 | // Collector. It collects the metrics from the provided Collector and sends |
| 67 | // their descriptors to the provided channel. |
| 68 | // |
| 69 | // If a Collector collects the same metrics throughout its lifetime, its |
| 70 | // Describe method can simply be implemented as: |
| 71 | // |
| 72 | // func (c customCollector) Describe(ch chan<- *Desc) { |
| 73 | // DescribeByCollect(c, ch) |
| 74 | // } |
| 75 | // |
| 76 | // However, this will not work if the metrics collected change dynamically over |
| 77 | // the lifetime of the Collector in a way that their combined set of descriptors |
| 78 | // changes as well. The shortcut implementation will then violate the contract |
| 79 | // of the Describe method. If a Collector sometimes collects no metrics at all |
| 80 | // (for example vectors like CounterVec, GaugeVec, etc., which only collect |
| 81 | // metrics after a metric with a fully specified label set has been accessed), |
| 82 | // it might even get registered as an unchecked Collecter (cf. the Register |
| 83 | // method of the Registerer interface). Hence, only use this shortcut |
| 84 | // implementation of Describe if you are certain to fulfill the contract. |
| 85 | // |
| 86 | // The Collector example demonstrates a use of DescribeByCollect. |
| 87 | func DescribeByCollect(c Collector, descs chan<- *Desc) { |
| 88 | metrics := make(chan Metric) |
| 89 | go func() { |
| 90 | c.Collect(metrics) |
| 91 | close(metrics) |
| 92 | }() |
| 93 | for m := range metrics { |
| 94 | descs <- m.Desc() |
| 95 | } |
| 96 | } |
| 97 | |
| 98 | // selfCollector implements Collector for a single Metric so that the Metric |
| 99 | // collects itself. Add it as an anonymous field to a struct that implements |
| 100 | // Metric, and call init with the Metric itself as an argument. |
| 101 | type selfCollector struct { |
| 102 | self Metric |
| 103 | } |
| 104 | |
| 105 | // init provides the selfCollector with a reference to the metric it is supposed |
| 106 | // to collect. It is usually called within the factory function to create a |
| 107 | // metric. See example. |
| 108 | func (c *selfCollector) init(self Metric) { |
| 109 | c.self = self |
| 110 | } |
| 111 | |
| 112 | // Describe implements Collector. |
| 113 | func (c *selfCollector) Describe(ch chan<- *Desc) { |
| 114 | ch <- c.self.Desc() |
| 115 | } |
| 116 | |
| 117 | // Collect implements Collector. |
| 118 | func (c *selfCollector) Collect(ch chan<- Metric) { |
| 119 | ch <- c.self |
| 120 | } |