[chore] Add Go runtime and host metrics (#4137)

Daenney is a dummy and forgot to add these when he revamped the OTEL stuff.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4137
Co-authored-by: Daenney <daenney@noreply.codeberg.org>
Co-committed-by: Daenney <daenney@noreply.codeberg.org>

vendor/go.opentelemetry.io/contrib/instrumentation/runtime/internal/deprecatedruntime/doc.go

@@ -0,0 +1,22 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+// Package deprecatedruntime implements the deprecated runtime metrics for OpenTelemetry.
+//
+// The metric events produced are:
+//
+//	runtime.go.cgo.calls         -          Number of cgo calls made by the current process
+//	runtime.go.gc.count          -          Number of completed garbage collection cycles
+//	runtime.go.gc.pause_ns       (ns)       Amount of nanoseconds in GC stop-the-world pauses
+//	runtime.go.gc.pause_total_ns (ns)       Cumulative nanoseconds in GC stop-the-world pauses since the program started
+//	runtime.go.goroutines        -          Number of goroutines that currently exist
+//	runtime.go.lookups           -          Number of pointer lookups performed by the runtime
+//	runtime.go.mem.heap_alloc    (bytes)    Bytes of allocated heap objects
+//	runtime.go.mem.heap_idle     (bytes)    Bytes in idle (unused) spans
+//	runtime.go.mem.heap_inuse    (bytes)    Bytes in in-use spans
+//	runtime.go.mem.heap_objects  -          Number of allocated heap objects
+//	runtime.go.mem.heap_released (bytes)    Bytes of idle spans whose physical memory has been returned to the OS
+//	runtime.go.mem.heap_sys      (bytes)    Bytes of heap memory obtained from the OS
+//	runtime.go.mem.live_objects  -          Number of live objects is the number of cumulative Mallocs - Frees
+//	runtime.uptime               (ms)       Milliseconds since application was initialized
+package deprecatedruntime // import "go.opentelemetry.io/contrib/instrumentation/runtime/internal/deprecatedruntime"

vendor/go.opentelemetry.io/contrib/instrumentation/runtime/internal/deprecatedruntime/runtime.go

@@ -0,0 +1,296 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package deprecatedruntime // import "go.opentelemetry.io/contrib/instrumentation/runtime/internal/deprecatedruntime"
+
+import (
+	"context"
+	"math"
+	goruntime "runtime"
+	"sync"
+	"time"
+
+	"go.opentelemetry.io/otel/metric"
+)
+
+// Runtime reports the work-in-progress conventional runtime metrics specified by OpenTelemetry.
+type runtime struct {
+	minimumReadMemStatsInterval time.Duration
+	meter                       metric.Meter
+}
+
+// Start initializes reporting of runtime metrics using the supplied config.
+func Start(meter metric.Meter, minimumReadMemStatsInterval time.Duration) error {
+	r := &runtime{
+		meter:                       meter,
+		minimumReadMemStatsInterval: minimumReadMemStatsInterval,
+	}
+	return r.register()
+}
+
+func (r *runtime) register() error {
+	startTime := time.Now()
+	uptime, err := r.meter.Int64ObservableCounter(
+		"runtime.uptime",
+		metric.WithUnit("ms"),
+		metric.WithDescription("Milliseconds since application was initialized"),
+	)
+	if err != nil {
+		return err
+	}
+
+	goroutines, err := r.meter.Int64ObservableUpDownCounter(
+		"process.runtime.go.goroutines",
+		metric.WithDescription("Number of goroutines that currently exist"),
+	)
+	if err != nil {
+		return err
+	}
+
+	cgoCalls, err := r.meter.Int64ObservableUpDownCounter(
+		"process.runtime.go.cgo.calls",
+		metric.WithDescription("Number of cgo calls made by the current process"),
+	)
+	if err != nil {
+		return err
+	}
+
+	_, err = r.meter.RegisterCallback(
+		func(ctx context.Context, o metric.Observer) error {
+			o.ObserveInt64(uptime, time.Since(startTime).Milliseconds())
+			o.ObserveInt64(goroutines, int64(goruntime.NumGoroutine()))
+			o.ObserveInt64(cgoCalls, goruntime.NumCgoCall())
+			return nil
+		},
+		uptime,
+		goroutines,
+		cgoCalls,
+	)
+	if err != nil {
+		return err
+	}
+
+	return r.registerMemStats()
+}
+
+func (r *runtime) registerMemStats() error {
+	var (
+		err error
+
+		heapAlloc    metric.Int64ObservableUpDownCounter
+		heapIdle     metric.Int64ObservableUpDownCounter
+		heapInuse    metric.Int64ObservableUpDownCounter
+		heapObjects  metric.Int64ObservableUpDownCounter
+		heapReleased metric.Int64ObservableUpDownCounter
+		heapSys      metric.Int64ObservableUpDownCounter
+		liveObjects  metric.Int64ObservableUpDownCounter
+
+		// TODO: is ptrLookups useful? I've not seen a value
+		// other than zero.
+		ptrLookups metric.Int64ObservableCounter
+
+		gcCount      metric.Int64ObservableCounter
+		pauseTotalNs metric.Int64ObservableCounter
+		gcPauseNs    metric.Int64Histogram
+
+		lastNumGC    uint32
+		lastMemStats time.Time
+		memStats     goruntime.MemStats
+
+		// lock prevents a race between batch observer and instrument registration.
+		lock sync.Mutex
+	)
+
+	lock.Lock()
+	defer lock.Unlock()
+
+	if heapAlloc, err = r.meter.Int64ObservableUpDownCounter(
+		"process.runtime.go.mem.heap_alloc",
+		metric.WithUnit("By"),
+		metric.WithDescription("Bytes of allocated heap objects"),
+	); err != nil {
+		return err
+	}
+
+	if heapIdle, err = r.meter.Int64ObservableUpDownCounter(
+		"process.runtime.go.mem.heap_idle",
+		metric.WithUnit("By"),
+		metric.WithDescription("Bytes in idle (unused) spans"),
+	); err != nil {
+		return err
+	}
+
+	if heapInuse, err = r.meter.Int64ObservableUpDownCounter(
+		"process.runtime.go.mem.heap_inuse",
+		metric.WithUnit("By"),
+		metric.WithDescription("Bytes in in-use spans"),
+	); err != nil {
+		return err
+	}
+
+	if heapObjects, err = r.meter.Int64ObservableUpDownCounter(
+		"process.runtime.go.mem.heap_objects",
+		metric.WithDescription("Number of allocated heap objects"),
+	); err != nil {
+		return err
+	}
+
+	// FYI see https://github.com/golang/go/issues/32284 to help
+	// understand the meaning of this value.
+	if heapReleased, err = r.meter.Int64ObservableUpDownCounter(
+		"process.runtime.go.mem.heap_released",
+		metric.WithUnit("By"),
+		metric.WithDescription("Bytes of idle spans whose physical memory has been returned to the OS"),
+	); err != nil {
+		return err
+	}
+
+	if heapSys, err = r.meter.Int64ObservableUpDownCounter(
+		"process.runtime.go.mem.heap_sys",
+		metric.WithUnit("By"),
+		metric.WithDescription("Bytes of heap memory obtained from the OS"),
+	); err != nil {
+		return err
+	}
+
+	if ptrLookups, err = r.meter.Int64ObservableCounter(
+		"process.runtime.go.mem.lookups",
+		metric.WithDescription("Number of pointer lookups performed by the runtime"),
+	); err != nil {
+		return err
+	}
+
+	if liveObjects, err = r.meter.Int64ObservableUpDownCounter(
+		"process.runtime.go.mem.live_objects",
+		metric.WithDescription("Number of live objects is the number of cumulative Mallocs - Frees"),
+	); err != nil {
+		return err
+	}
+
+	if gcCount, err = r.meter.Int64ObservableCounter(
+		"process.runtime.go.gc.count",
+		metric.WithDescription("Number of completed garbage collection cycles"),
+	); err != nil {
+		return err
+	}
+
+	// Note that the following could be derived as a sum of
+	// individual pauses, but we may lose individual pauses if the
+	// observation interval is too slow.
+	if pauseTotalNs, err = r.meter.Int64ObservableCounter(
+		"process.runtime.go.gc.pause_total_ns",
+		// TODO: nanoseconds units
+		metric.WithDescription("Cumulative nanoseconds in GC stop-the-world pauses since the program started"),
+	); err != nil {
+		return err
+	}
+
+	if gcPauseNs, err = r.meter.Int64Histogram(
+		"process.runtime.go.gc.pause_ns",
+		// TODO: nanoseconds units
+		metric.WithDescription("Amount of nanoseconds in GC stop-the-world pauses"),
+	); err != nil {
+		return err
+	}
+
+	_, err = r.meter.RegisterCallback(
+		func(ctx context.Context, o metric.Observer) error {
+			lock.Lock()
+			defer lock.Unlock()
+
+			now := time.Now()
+			if now.Sub(lastMemStats) >= r.minimumReadMemStatsInterval {
+				goruntime.ReadMemStats(&memStats)
+				lastMemStats = now
+			}
+
+			o.ObserveInt64(heapAlloc, clampUint64(memStats.HeapAlloc))
+			o.ObserveInt64(heapIdle, clampUint64(memStats.HeapIdle))
+			o.ObserveInt64(heapInuse, clampUint64(memStats.HeapInuse))
+			o.ObserveInt64(heapObjects, clampUint64(memStats.HeapObjects))
+			o.ObserveInt64(heapReleased, clampUint64(memStats.HeapReleased))
+			o.ObserveInt64(heapSys, clampUint64(memStats.HeapSys))
+			o.ObserveInt64(liveObjects, clampUint64(memStats.Mallocs-memStats.Frees))
+			o.ObserveInt64(ptrLookups, clampUint64(memStats.Lookups))
+			o.ObserveInt64(gcCount, int64(memStats.NumGC))
+			o.ObserveInt64(pauseTotalNs, clampUint64(memStats.PauseTotalNs))
+
+			computeGCPauses(ctx, gcPauseNs, memStats.PauseNs[:], lastNumGC, memStats.NumGC)
+
+			lastNumGC = memStats.NumGC
+
+			return nil
+		},
+		heapAlloc,
+		heapIdle,
+		heapInuse,
+		heapObjects,
+		heapReleased,
+		heapSys,
+		liveObjects,
+
+		ptrLookups,
+
+		gcCount,
+		pauseTotalNs,
+	)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func clampUint64(v uint64) int64 {
+	if v > math.MaxInt64 {
+		return math.MaxInt64
+	}
+	return int64(v) // nolint: gosec  // Overflow checked above.
+}
+
+func computeGCPauses(
+	ctx context.Context,
+	recorder metric.Int64Histogram,
+	circular []uint64,
+	lastNumGC, currentNumGC uint32,
+) {
+	delta := int(int64(currentNumGC) - int64(lastNumGC))
+
+	if delta == 0 {
+		return
+	}
+
+	if delta >= len(circular) {
+		// There were > 256 collections, some may have been lost.
+		recordGCPauses(ctx, recorder, circular)
+		return
+	}
+
+	n := len(circular)
+	if n < 0 {
+		// Only the case in error situations.
+		return
+	}
+
+	length := uint64(n) // nolint: gosec  // n >= 0
+
+	i := uint64(lastNumGC) % length
+	j := uint64(currentNumGC) % length
+
+	if j < i { // wrap around the circular buffer
+		recordGCPauses(ctx, recorder, circular[i:])
+		recordGCPauses(ctx, recorder, circular[:j])
+		return
+	}
+
+	recordGCPauses(ctx, recorder, circular[i:j])
+}
+
+func recordGCPauses(
+	ctx context.Context,
+	recorder metric.Int64Histogram,
+	pauses []uint64,
+) {
+	for _, pause := range pauses {
+		recorder.Record(ctx, clampUint64(pause))
+	}
+}