runtime,runtime/metrics: add memory metrics

This change adds support for a variety of runtime memory metrics and
contains the base implementation of Read for the runtime/metrics
package, which lives in the runtime.

It also adds testing infrastructure for the metrics package, and a bunch
of format and documentation tests.

For #37112.

Change-Id: I16a2c4781eeeb2de0abcb045c15105f1210e2d8a
Reviewed-on: https://go-review.googlesource.com/c/go/+/247041
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
Trust: Michael Knyszek <mknyszek@google.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/src/runtime/metrics/sample.go b/src/runtime/metrics/sample.go
index c7a3fc424a..b4b0979aa6 100644
--- a/src/runtime/metrics/sample.go
+++ b/src/runtime/metrics/sample.go
@@ -4,6 +4,11 @@
 
 package metrics
 
+import (
+	_ "runtime" // depends on the runtime via a linkname'd function
+	"unsafe"
+)
+
 // Sample captures a single metric sample.
 type Sample struct {
 	// Name is the name of the metric sampled.
@@ -16,6 +21,9 @@ type Sample struct {
 	Value Value
 }
 
+// Implemented in the runtime.
+func runtime_readMetrics(unsafe.Pointer, int, int)
+
 // Read populates each Value field in the given slice of metric samples.
 //
 // Desired metrics should be present in the slice with the appropriate name.
@@ -25,5 +33,5 @@ type Sample struct {
 // will have the value populated as KindBad to indicate that the name is
 // unknown.
 func Read(m []Sample) {
-	panic("unimplemented")
+	runtime_readMetrics(unsafe.Pointer(&m[0]), len(m), cap(m))
 }