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480b2ca07c
* [NOD-294] Fix golint in deploy.sh and fixed all lint errors * [NOD-294] Fix typos in comments * [NOD-294] Convert VirtualForTest into alias of *virtualBlock * [NOD-294] Fixed some more typos in comments
80 lines
2.5 KiB
Go
80 lines
2.5 KiB
Go
package locks
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import (
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"sync"
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)
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// PriorityMutex is a read-write mutex with an additional low
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// priority lock. It's implemented with the following
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// components:
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// * Data mutex: The actual lock on the data structure. Its
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// type is sync.RWMutex for its high priority read lock.
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// * High priority waiting group: A waiting group that is being
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// incremented every time a high priority lock (read or write)
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// is acquired, and decremented every time a high priority lock is
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// unlocked. Low priority locks can start being held only
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// when the waiting group is empty.
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// * Low priority mutex: This mutex ensures that when the
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// waiting group is empty, only one low priority lock
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// will be able to lock the data mutex.
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// PriorityMutex implements a lock with three priorities:
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// * High priority write lock - locks the mutex with the highest priority.
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// * High priority read lock - locks the mutex with lower priority than
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// the high priority write lock. Can be held concurrently with other
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// with other read locks.
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// * Low priority write lock - locks the mutex with lower priority then
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// the read lock.
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type PriorityMutex struct {
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dataMutex sync.RWMutex
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highPriorityWaiting *waitGroup
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lowPriorityMutex sync.Mutex
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}
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// NewPriorityMutex returns a new priority mutex
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func NewPriorityMutex() *PriorityMutex {
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lock := PriorityMutex{
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highPriorityWaiting: newWaitGroup(),
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}
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return &lock
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}
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// LowPriorityWriteLock acquires a low-priority write lock.
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func (mtx *PriorityMutex) LowPriorityWriteLock() {
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mtx.lowPriorityMutex.Lock()
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mtx.highPriorityWaiting.wait()
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mtx.dataMutex.Lock()
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}
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// LowPriorityWriteUnlock unlocks the low-priority write lock
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func (mtx *PriorityMutex) LowPriorityWriteUnlock() {
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mtx.dataMutex.Unlock()
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mtx.lowPriorityMutex.Unlock()
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}
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// HighPriorityWriteLock acquires a high-priority write lock.
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func (mtx *PriorityMutex) HighPriorityWriteLock() {
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mtx.highPriorityWaiting.add()
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mtx.dataMutex.Lock()
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}
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// HighPriorityWriteUnlock unlocks the high-priority write lock
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func (mtx *PriorityMutex) HighPriorityWriteUnlock() {
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mtx.dataMutex.Unlock()
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mtx.highPriorityWaiting.done()
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}
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// HighPriorityReadLock acquires a high-priority read
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// lock.
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func (mtx *PriorityMutex) HighPriorityReadLock() {
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mtx.highPriorityWaiting.add()
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mtx.dataMutex.RLock()
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}
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// HighPriorityReadUnlock unlocks the high-priority read
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// lock
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func (mtx *PriorityMutex) HighPriorityReadUnlock() {
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mtx.highPriorityWaiting.done()
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mtx.dataMutex.RUnlock()
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}
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