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60 lines
2.0 KiB
Go
60 lines
2.0 KiB
Go
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// Copyright The OpenTelemetry Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package metric // import "go.opentelemetry.io/otel/sdk/metric"
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import (
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"sync/atomic"
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)
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// refcountMapped atomically counts the number of references (usages) of an entry
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// while also keeping a state of mapped/unmapped into a different data structure
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// (an external map or list for example).
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//
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// refcountMapped uses an atomic value where the least significant bit is used to
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// keep the state of mapping ('1' is used for unmapped and '0' is for mapped) and
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// the rest of the bits are used for refcounting.
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type refcountMapped struct {
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// refcount has to be aligned for 64-bit atomic operations.
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value int64
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}
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// ref returns true if the entry is still mapped and increases the
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// reference usages, if unmapped returns false.
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func (rm *refcountMapped) ref() bool {
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// Check if this entry was marked as unmapped between the moment
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// we got a reference to it (or will be removed very soon) and here.
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return atomic.AddInt64(&rm.value, 2)&1 == 0
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}
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func (rm *refcountMapped) unref() {
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atomic.AddInt64(&rm.value, -2)
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}
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// tryUnmap flips the mapped bit to "unmapped" state and returns true if both of the
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// following conditions are true upon entry to this function:
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// * There are no active references;
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// * The mapped bit is in "mapped" state.
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// Otherwise no changes are done to mapped bit and false is returned.
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func (rm *refcountMapped) tryUnmap() bool {
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if atomic.LoadInt64(&rm.value) != 0 {
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return false
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}
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return atomic.CompareAndSwapInt64(
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&rm.value,
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0,
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1,
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)
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}
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