// Copyright 2019, OpenTelemetry 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. // metric package provides an API for reporting diagnostic // measurements using three basic kinds of instruments (or four, if // calling one special case a separate one). // // The three basic kinds are: // // - counters // - gauges // - measures // // All instruments report either float64 or int64 values. // // The primary object that handles metrics is Meter. The // implementation of the Meter is provided by SDK. Normally, the Meter // is used directly only for the LabelSet generation, batch recording // and the handle destruction. // // LabelSet is a set of keys and values that are in a suitable, // optimized form to be used by Meter. // // Counters are instruments that are reporting a quantity or a sum. An // example could be bank account balance or bytes downloaded. Counters // can be created with either NewFloat64Counter or // NewInt64Counter. Counters expect non-negative values by default to // be reported. This can be changed with the WithMonotonic option // (passing false as a parameter) passed to the Meter.New*Counter // function - this allows reporting negative values. To report the new // value, use an Add function. // // Gauges are instruments that are reporting a current state of a // value. An example could be voltage or temperature. Gauges can be // created with either NewFloat64Gauge or NewInt64Gauge. Gauges by // default have no limitations about reported values - they can be // less or greater than the last reported value. This can be changed // with the WithMonotonic option passed to the New*Gauge function - // this permits the reported values only to go up. To report a new // value, use the Set function. // // Measures are instruments that are reporting values that are // recorded separately to figure out some statistical properties from // those values (like average). An example could be temperature over // time or lines of code in the project over time. Measures can be // created with either NewFloat64Measure or NewInt64Measure. Measures // by default take only non-negative values. This can be changed with // the WithAbsolute option (passing false as a parameter) passed to // the New*Measure function - this allows reporting negative values // too. To report a new value, use the Record function. // // All the basic kinds of instruments also support creating handles // for a potentially more efficient reporting. The handles have the // same function names as the instruments (so counter handle has Add, // gauge handle has Set and measure handle has Record). Handles can be // created with the AcquireHandle function of the respective // instrument. When done with the handle, call Release on it. package metric // import "go.opentelemetry.io/otel/api/metric"