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// _ _
// __ _____ __ ___ ___ __ _| |_ ___
// \ \ /\ / / _ \/ _` \ \ / / |/ _` | __/ _ \
// \ V V / __/ (_| |\ V /| | (_| | || __/
// \_/\_/ \___|\__,_| \_/ |_|\__,_|\__\___|
//
// Copyright © 2016 - 2024 Weaviate B.V. All rights reserved.
//
// CONTACT: [email protected]
//
package common
import "sync"
const DefaultShardedLocksCount = 512
type ShardedLocks struct {
// number of locks
count int
// ensures single LockAll and multiple RLockAll, Lock and RLock
// LockAll is exclusive to RLockAll, Lock, RLock
writeAll *sync.RWMutex
// indicates whether write of any single shard is ongoing, exclusive with readAll
writeAny *sync.RWMutex
// indicates whether read of all shards is ongoing, exclusive with writeAny
readAll *sync.RWMutex
// allows safe transition between writeAny and readAll
change *sync.RWMutex
// sharded locks
shards []*sync.RWMutex
}
func NewDefaultShardedLocks() *ShardedLocks {
return NewShardedLocks(DefaultShardedLocksCount)
}
func NewShardedLocks(count int) *ShardedLocks {
if count < 2 {
count = 2
}
writeAll := new(sync.RWMutex)
writeAny := new(sync.RWMutex)
readAll := new(sync.RWMutex)
change := new(sync.RWMutex)
shards := make([]*sync.RWMutex, count)
for i := 0; i < count; i++ {
shards[i] = new(sync.RWMutex)
}
return &ShardedLocks{
count: count,
writeAll: writeAll,
readAll: readAll,
writeAny: writeAny,
change: change,
shards: shards,
}
}
func (sl *ShardedLocks) LockAll() {
sl.writeAll.Lock()
}
func (sl *ShardedLocks) UnlockAll() {
sl.writeAll.Unlock()
}
func (sl *ShardedLocks) LockedAll(callback func()) {
sl.LockAll()
defer sl.UnlockAll()
callback()
}
func (sl *ShardedLocks) Lock(id uint64) {
sl.writeAll.RLock()
sl.markOngoingWriteAny()
sl.shards[sl.mid(id)].Lock()
}
func (sl *ShardedLocks) Unlock(id uint64) {
sl.shards[sl.mid(id)].Unlock()
sl.writeAny.RUnlock()
sl.writeAll.RUnlock()
}
func (sl *ShardedLocks) Locked(id uint64, callback func()) {
sl.Lock(id)
defer sl.Unlock(id)
callback()
}
func (sl *ShardedLocks) RLockAll() {
sl.writeAll.RLock()
sl.markOngoingReadAll()
}
func (sl *ShardedLocks) RUnlockAll() {
sl.readAll.RUnlock()
sl.writeAll.RUnlock()
}
func (sl *ShardedLocks) RLockedAll(callback func()) {
sl.RLockAll()
defer sl.RUnlockAll()
callback()
}
func (sl *ShardedLocks) RLock(id uint64) {
sl.writeAll.RLock()
sl.shards[sl.mid(id)].RLock()
}
func (sl *ShardedLocks) RUnlock(id uint64) {
sl.shards[sl.mid(id)].RUnlock()
sl.writeAll.RUnlock()
}
func (sl *ShardedLocks) RLocked(id uint64, callback func()) {
sl.RLock(id)
defer sl.RUnlock(id)
callback()
}
func (sl *ShardedLocks) mid(id uint64) uint64 {
return id % uint64(sl.count)
}
func (sl *ShardedLocks) markOngoingWriteAny() {
sl.change.RLock()
defer sl.change.RUnlock()
// wait until no ongoing readAll
sl.readAll.Lock()
// mark ongoing writeAny
sl.writeAny.RLock()
sl.readAll.Unlock()
}
func (sl *ShardedLocks) markOngoingReadAll() {
sl.change.Lock()
defer sl.change.Unlock()
// wait until no ongoing writeAny
sl.writeAny.Lock()
// mark ongoing readAll
sl.readAll.RLock()
sl.writeAny.Unlock()
}
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