60 lines
2.0 KiB
Go
60 lines
2.0 KiB
Go
// Copyright The OpenTelemetry 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.
|
|
|
|
package metric // import "go.opentelemetry.io/otel/sdk/metric"
|
|
|
|
import (
|
|
"sync/atomic"
|
|
)
|
|
|
|
// refcountMapped atomically counts the number of references (usages) of an entry
|
|
// while also keeping a state of mapped/unmapped into a different data structure
|
|
// (an external map or list for example).
|
|
//
|
|
// refcountMapped uses an atomic value where the least significant bit is used to
|
|
// keep the state of mapping ('1' is used for unmapped and '0' is for mapped) and
|
|
// the rest of the bits are used for refcounting.
|
|
type refcountMapped struct {
|
|
// refcount has to be aligned for 64-bit atomic operations.
|
|
value int64
|
|
}
|
|
|
|
// ref returns true if the entry is still mapped and increases the
|
|
// reference usages, if unmapped returns false.
|
|
func (rm *refcountMapped) ref() bool {
|
|
// Check if this entry was marked as unmapped between the moment
|
|
// we got a reference to it (or will be removed very soon) and here.
|
|
return atomic.AddInt64(&rm.value, 2)&1 == 0
|
|
}
|
|
|
|
func (rm *refcountMapped) unref() {
|
|
atomic.AddInt64(&rm.value, -2)
|
|
}
|
|
|
|
// tryUnmap flips the mapped bit to "unmapped" state and returns true if both of the
|
|
// following conditions are true upon entry to this function:
|
|
// * There are no active references;
|
|
// * The mapped bit is in "mapped" state.
|
|
// Otherwise no changes are done to mapped bit and false is returned.
|
|
func (rm *refcountMapped) tryUnmap() bool {
|
|
if atomic.LoadInt64(&rm.value) != 0 {
|
|
return false
|
|
}
|
|
return atomic.CompareAndSwapInt64(
|
|
&rm.value,
|
|
0,
|
|
1,
|
|
)
|
|
}
|