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79 lines
2.2 KiB
Go
79 lines
2.2 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/atomic"
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"time"
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)
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// A LMutex is a mutual exclusion lock with timeouts.
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type LMutex struct {
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state int64
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}
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// NewLMutex - initializes a new lsync mutex.
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func NewLMutex() *LMutex {
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return &LMutex{}
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}
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// Lock holds a lock on lm.
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//
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// If the lock is already in use, the calling go routine
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// blocks until the mutex is available.
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func (lm *LMutex) Lock() {
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lm.lockLoop(time.Duration(1<<63 - 1))
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}
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// GetLock tries to get a write lock on lm before the timeout occurs.
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func (lm *LMutex) GetLock(timeout time.Duration) (locked bool) {
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return lm.lockLoop(timeout)
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}
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// lockLoop will acquire either a read or a write lock
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//
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// The call will block until the lock is granted using a built-in
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// timing randomized back-off algorithm to try again until successful
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func (lm *LMutex) lockLoop(timeout time.Duration) bool {
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doneCh, start := make(chan struct{}), time.Now().UTC()
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defer close(doneCh)
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// We timed out on the previous lock, incrementally wait
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// for a longer back-off time and try again afterwards.
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for range newRetryTimerSimple(doneCh) {
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// Try to acquire the lock.
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if atomic.CompareAndSwapInt64(&lm.state, NOLOCKS, WRITELOCK) {
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return true
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} else if time.Now().UTC().Sub(start) >= timeout { // Are we past the timeout?
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break
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}
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// We timed out on the previous lock, incrementally wait
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// for a longer back-off time and try again afterwards.
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}
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return false
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}
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// Unlock unlocks the lock.
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//
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// It is a run-time error if lm is not locked on entry to Unlock.
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func (lm *LMutex) Unlock() {
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if !atomic.CompareAndSwapInt64(&lm.state, WRITELOCK, NOLOCKS) {
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panic("Trying to Unlock() while no Lock() is active")
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}
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}
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