1 // Copyright 2020 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 package metrics 6 7 import ( 8 _ "runtime" // depends on the runtime via a linkname'd function 9 "unsafe" 10 ) 11 12 // Sample captures a single metric sample. 13 type Sample struct { 14 // Name is the name of the metric sampled. 15 // 16 // It must correspond to a name in one of the metric descriptions 17 // returned by All. 18 Name string 19 20 // Value is the value of the metric sample. 21 Value Value 22 } 23 24 // Implemented in the runtime. 25 func runtime_readMetrics(unsafe.Pointer, int, int) 26 27 // Read populates each Value field in the given slice of metric samples. 28 // 29 // Desired metrics should be present in the slice with the appropriate name. 30 // The user of this API is encouraged to re-use the same slice between calls for 31 // efficiency, but is not required to do so. 32 // 33 // Note that re-use has some caveats. Notably, Values should not be read or 34 // manipulated while a Read with that value is outstanding; that is a data race. 35 // This property includes pointer-typed Values (for example, Float64Histogram) 36 // whose underlying storage will be reused by Read when possible. To safely use 37 // such values in a concurrent setting, all data must be deep-copied. 38 // 39 // It is safe to execute multiple Read calls concurrently, but their arguments 40 // must share no underlying memory. When in doubt, create a new []Sample from 41 // scratch, which is always safe, though may be inefficient. 42 // 43 // Sample values with names not appearing in All will have their Value populated 44 // as KindBad to indicate that the name is unknown. 45 func Read(m []Sample) { 46 runtime_readMetrics(unsafe.Pointer(&m[0]), len(m), cap(m)) 47 } 48