69 lines
1.7 KiB
Go
69 lines
1.7 KiB
Go
package core
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import (
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"sync"
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"sync/atomic"
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"time"
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)
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// UpgradeableMutex wraps a RWMutex and provides safe upgrading / downgrading
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// by informing you whether a write lock was achieved in the brief swap time
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type UpgradeableMutex struct {
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wLast int64
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internal sync.RWMutex
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}
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// RLock exactly wraps the internal RWMutex
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func (mu *UpgradeableMutex) RLock() {
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mu.internal.RLock()
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}
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// RUnlock exactly wraps the internal RWMutex
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func (mu *UpgradeableMutex) RUnlock() {
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mu.internal.RUnlock()
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}
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// Lock wraps the internal RWMutex, atomically storing the last write-lock time
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func (mu *UpgradeableMutex) Lock() {
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mu.internal.Lock()
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atomic.StoreInt64(&mu.wLast, time.Now().UnixNano())
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}
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// Unlock exactly wraps the internal RWMutex
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func (mu *UpgradeableMutex) Unlock() {
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mu.internal.Unlock()
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}
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// safeSwap stores the current time, performs the swap function and checks if
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// any write locks were achieved during the swap function
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func (mu *UpgradeableMutex) safeSwap(swapFn func()) bool {
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// Get the 'now' time
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now := time.Now().UnixNano()
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// Store now time
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atomic.StoreInt64(&mu.wLast, now)
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// Perform the swap
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swapFn()
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// Successful swap determined by if last write-lock
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// is still equal to 'now'
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return atomic.LoadInt64(&mu.wLast) == now
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}
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// UpgradeLock upgrades a read to a write lock, returning success state as a bool
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func (mu *UpgradeableMutex) UpgradeLock() bool {
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return mu.safeSwap(func() {
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mu.internal.RUnlock()
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mu.internal.Lock()
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})
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}
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// DowngradeLock downgrades a write to a read lock, returning success state as a bool
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func (mu *UpgradeableMutex) DowngradeLock() bool {
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return mu.safeSwap(func() {
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mu.internal.Unlock()
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mu.internal.RLock()
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})
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}
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