Initial commit

vendor/github.com/cockroachdb/pebble/internal/cache/refcnt_tracing.go

@@ -0,0 +1,66 @@
+// Copyright 2020 The LevelDB-Go and Pebble Authors. All rights reserved. Use
+// of this source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+//go:build tracing
+// +build tracing
+
+package cache
+
+import (
+	"fmt"
+	"runtime/debug"
+	"strings"
+	"sync"
+	"sync/atomic"
+)
+
+// refcnt provides an atomic reference count, along with a tracing facility for
+// debugging logic errors in manipulating the reference count. This version is
+// used when the "tracing" build tag is enabled.
+type refcnt struct {
+	val atomic.Int32
+	sync.Mutex
+	msgs []string
+}
+
+func (v *refcnt) init(val int32) {
+	v.val.Store(val)
+	v.trace("init")
+}
+
+func (v *refcnt) refs() int32 {
+	return v.val.Load()
+}
+
+func (v *refcnt) acquire() {
+	switch n := v.val.Add(1); {
+	case n <= 1:
+		panic(fmt.Sprintf("pebble: inconsistent reference count: %d", n))
+	}
+	v.trace("acquire")
+}
+
+func (v *refcnt) release() bool {
+	n := v.val.Add(-1)
+	switch {
+	case n < 0:
+		panic(fmt.Sprintf("pebble: inconsistent reference count: %d", n))
+	}
+	v.trace("release")
+	return n == 0
+}
+
+func (v *refcnt) trace(msg string) {
+	s := fmt.Sprintf("%s: refs=%d\n%s", msg, v.refs(), debug.Stack())
+	v.Lock()
+	v.msgs = append(v.msgs, s)
+	v.Unlock()
+}
+
+func (v *refcnt) traces() string {
+	v.Lock()
+	s := strings.Join(v.msgs, "\n")
+	v.Unlock()
+	return s
+}