Initial QSfera import

Server/vendor/github.com/nats-io/nats-server/v2/server/ats/ats.go

@@ -0,0 +1,86 @@
+// Copyright 2025 The NATS Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// ats controls the go routines for the access time service.
+// This allows more efficient unixnano operations for cache access times.
+// We will have one per binary (usually per server).
+package ats
+
+import (
+	"sync/atomic"
+	"time"
+)
+
+// Update every 100ms for gathering access time in unix nano.
+const TickInterval = 100 * time.Millisecond
+
+var (
+	// Our unix nano time.
+	utime atomic.Int64
+	// How may registered users do we have, controls lifetime of Go routine.
+	refs atomic.Int64
+	// To signal the shutdown of the Go routine.
+	done chan struct{}
+)
+
+func init() {
+	// Initialize our done chan.
+	done = make(chan struct{}, 1)
+}
+
+// Register usage. This will happen on filestore creation.
+func Register() {
+	if v := refs.Add(1); v == 1 {
+		// This is the first to register (could also go up and down),
+		// so spin up Go routine and grab initial time.
+		utime.Store(time.Now().UnixNano())
+
+		go func() {
+			ticker := time.NewTicker(TickInterval)
+			defer ticker.Stop()
+			for {
+				select {
+				case <-ticker.C:
+					utime.Store(time.Now().UnixNano())
+				case <-done:
+					return
+				}
+			}
+		}()
+	}
+}
+
+// Unregister usage. We will shutdown the go routine if no more registered users.
+func Unregister() {
+	if v := refs.Add(-1); v == 0 {
+		done <- struct{}{}
+	} else if v < 0 {
+		refs.Store(0)
+		panic("unbalanced unregister for access time state")
+	}
+}
+
+// Will load the access time from an atomic.
+// If no one has registered this will return 0 or stale data.
+// It is the responsibility of the user to properly register and unregister.
+func AccessTime() int64 {
+	// Return last updated time.
+	v := utime.Load()
+	if v == 0 {
+		// Always register a time, the worst case is a stale time.
+		// On startup, we can register in parallel and could previously panic.
+		v = time.Now().UnixNano()
+		utime.Store(v)
+	}
+	return v
+}