Initial QSfera import

Server/vendor/go.opentelemetry.io/otel/sdk/trace/evictedqueue.go

@@ -0,0 +1,64 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package trace // import "go.opentelemetry.io/otel/sdk/trace"
+
+import (
+	"slices"
+	"sync"
+
+	"go.opentelemetry.io/otel/internal/global"
+)
+
+// evictedQueue is a FIFO queue with a configurable capacity.
+type evictedQueue[T any] struct {
+	queue          []T
+	capacity       int
+	droppedCount   int
+	logDroppedMsg  string
+	logDroppedOnce sync.Once
+}
+
+func newEvictedQueueEvent(capacity int) evictedQueue[Event] {
+	// Do not pre-allocate queue, do this lazily.
+	return evictedQueue[Event]{
+		capacity:      capacity,
+		logDroppedMsg: "limit reached: dropping trace trace.Event",
+	}
+}
+
+func newEvictedQueueLink(capacity int) evictedQueue[Link] {
+	// Do not pre-allocate queue, do this lazily.
+	return evictedQueue[Link]{
+		capacity:      capacity,
+		logDroppedMsg: "limit reached: dropping trace trace.Link",
+	}
+}
+
+// add adds value to the evictedQueue eq. If eq is at capacity, the oldest
+// queued value will be discarded and the drop count incremented.
+func (eq *evictedQueue[T]) add(value T) {
+	if eq.capacity == 0 {
+		eq.droppedCount++
+		eq.logDropped()
+		return
+	}
+
+	if eq.capacity > 0 && len(eq.queue) == eq.capacity {
+		// Drop first-in while avoiding allocating more capacity to eq.queue.
+		copy(eq.queue[:eq.capacity-1], eq.queue[1:])
+		eq.queue = eq.queue[:eq.capacity-1]
+		eq.droppedCount++
+		eq.logDropped()
+	}
+	eq.queue = append(eq.queue, value)
+}
+
+func (eq *evictedQueue[T]) logDropped() {
+	eq.logDroppedOnce.Do(func() { global.Warn(eq.logDroppedMsg) })
+}
+
+// copy returns a copy of the evictedQueue.
+func (eq *evictedQueue[T]) copy() []T {
+	return slices.Clone(eq.queue)
+}