// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

/*
Package metrics provides a stable interface to access implementation-defined
metrics exported by the Go runtime. This package is similar to existing functions
like runtime.ReadMemStats and debug.ReadGCStats, but significantly more general.

The set of metrics defined by this package may evolve as the runtime itself
evolves, and also enables variation across Go implementations, whose relevant
metric sets may not intersect.

Interface

Metrics are designated by a string key, rather than, for example, a field name in
a struct. The full list of supported metrics is always available in the slice of
Descriptions returned by All. Each Description also includes useful information
about the metric, such as how to display it (e.g. gauge vs. counter) and how difficult
or disruptive it is to obtain it (e.g. do you need to stop the world?).

Thus, users of this API are encouraged to sample supported metrics defined by the
slice returned by All to remain compatible across Go versions. Of course, situations
arise where reading specific metrics is critical. For these cases, users are
encouranged to use build tags, and although metrics may be deprecated and removed,
users should consider this to be an exceptional and rare event, coinciding with a
very large change in a particular Go implementation.

Each metric key also has a "kind" that describes the format of the metric's value.
In the interest of not breaking users of this package, the "kind" for a given metric
is guaranteed not to change. If it must change, then a new metric will be introduced
with a new key and a new "kind."

Metric key format

As mentioned earlier, metric keys are strings. Their format is simple and well-defined,
designed to be both human and machine readable. It is split into two components,
separated by a colon: a rooted path and a unit. The choice to include the unit in
the key is motivated by compatibility: if a metric's unit changes, its semantics likely
did also, and a new key should be introduced.

For more details on the precise definition of the metric key's path and unit formats, see
the documentation of the Name field of the Description struct.

Supported metrics

TODO(mknyszek): List them here as they're added.
*/
package metrics