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runtime/metrics: expand Read documention with caveats

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This change modifies the documentation of Read with some caveats about
reusing the slice passed in to Read as well as with what concurrent
situations are safe.

Change-Id: I76fd31acc67ae384546a8442dfbf9d16b7445cff
Reviewed-on: https://go-review.googlesource.com/c/go/+/275853
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
This commit is contained in:
Michael Anthony Knyszek 2020-12-07 15:03:51 +00:00 committed by Michael Knyszek
parent d0f40d2922
commit e0d20e52ee
1 changed files with 10 additions and 0 deletions
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10
src/runtime/metrics/sample.go
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@ -30,6 +30,16 @@ func runtime_readMetrics(unsafe.Pointer, int, int)
// The user of this API is encouraged to re-use the same slice between calls for
// efficiency, but is not required to do so.
//
// Note that re-use has some caveats. Notably, Values should not be read or
// manipulated while a Read with that value is outstanding; that is a data race.
// This property includes pointer-typed Values (e.g. Float64Histogram) whose
// underlying storage will be reused by Read when possible. To safely use such
// values in a concurrent setting, all data must be deep-copied.
//
// It is safe to execute multiple Read calls concurrently, but their arguments
// must share no underlying memory. When in doubt, create a new []Sample from
// scratch, which is always safe, though may be inefficient.
//
// Sample values with names not appearing in All will have their Value populated
// as KindBad to indicate that the name is unknown.
func Read(m []Sample) {