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65 lines
2.1 KiB
Go
65 lines
2.1 KiB
Go
/*
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* Minio Cloud Storage, (C) 2017 Minio, Inc.
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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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*/
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package lsync
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import (
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"sync"
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"sync/atomic"
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)
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// LFrequentAccess is a synchronization mechanism for frequently read yet
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// infrequently updated data structures. It uses a copy-on-write paradigm
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// for updates to the data.
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type LFrequentAccess struct {
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state atomic.Value
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writeLock sync.Mutex
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locked bool
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}
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// NewLFrequentAccess - initializes a new LFrequentAccess.
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func NewLFrequentAccess(x interface{}) *LFrequentAccess {
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lm := &LFrequentAccess{}
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lm.state.Store(x)
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return lm
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}
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// ReadOnlyAccess returns the data intented for reads without further synchronization
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func (lm *LFrequentAccess) ReadOnlyAccess() (constReadOnly interface{}) {
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return lm.state.Load()
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}
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// LockBeforeSet must be called before updates of the data in order to synchronize
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// with other potential writers. It returns the current version of the data that
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// needs to be copied over into a new version.
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func (lm *LFrequentAccess) LockBeforeSet() (constCurVersion interface{}) {
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lm.writeLock.Lock()
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lm.locked = true
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return lm.state.Load()
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}
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// SetNewCopyAndUnlock updates the data with a new modified copy and unlocks
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// simultaneously. Make sure to call LockBeforeSet beforehand to synchronize
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// between potential parallel writers (and not lose any updated information).
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func (lm *LFrequentAccess) SetNewCopyAndUnlock(newCopy interface{}) {
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if !lm.locked {
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panic("SetNewCopyAndUnlock: locked state is false (did you call LockBeforeSet?)")
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}
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lm.state.Store(newCopy)
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lm.locked = false
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lm.writeLock.Unlock()
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}
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