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|
package util
import (
"fmt"
"github.com/seaweedfs/seaweedfs/weed/glog"
"sync"
"sync/atomic"
)
// LockTable is a table of locks that can be acquired.
// Locks are acquired in order of request.
type LockTable[T comparable] struct {
mu sync.Mutex
locks map[T]*LockEntry
lockIdSeq int64
}
type LockEntry struct {
mu sync.Mutex
waiters []*ActiveLock // ordered waiters that are blocked by exclusive locks
activeLockOwnerCount int32
lockType LockType
cond *sync.Cond
}
type LockType int
const (
SharedLock LockType = iota
ExclusiveLock
)
type ActiveLock struct {
ID int64
isDeleted bool
intention string // for debugging
}
func NewLockTable[T comparable]() *LockTable[T] {
return &LockTable[T]{
locks: make(map[T]*LockEntry),
}
}
func (lt *LockTable[T]) NewActiveLock(intention string) *ActiveLock {
id := atomic.AddInt64(<.lockIdSeq, 1)
l := &ActiveLock{ID: id, intention: intention}
return l
}
func (lt *LockTable[T]) AcquireLock(intention string, key T, lockType LockType) (lock *ActiveLock) {
lt.mu.Lock()
// Get or create the lock entry for the key
entry, exists := lt.locks[key]
if !exists {
entry = &LockEntry{}
entry.cond = sync.NewCond(&entry.mu)
lt.locks[key] = entry
}
lt.mu.Unlock()
lock = lt.NewActiveLock(intention)
// If the lock is held exclusively, wait
entry.mu.Lock()
if len(entry.waiters) > 0 || lockType == ExclusiveLock {
glog.V(4).Infof("ActiveLock %d %s wait for %+v type=%v with waiters %d active %d.\n", lock.ID, lock.intention, key, lockType, len(entry.waiters), entry.activeLockOwnerCount)
if len(entry.waiters) > 0 {
for _, waiter := range entry.waiters {
fmt.Printf(" %d", waiter.ID)
}
fmt.Printf("\n")
}
entry.waiters = append(entry.waiters, lock)
if lockType == ExclusiveLock {
for !lock.isDeleted && ((len(entry.waiters) > 0 && lock.ID != entry.waiters[0].ID) || entry.activeLockOwnerCount > 0) {
entry.cond.Wait()
}
} else {
for !lock.isDeleted && (len(entry.waiters) > 0 && lock.ID != entry.waiters[0].ID) {
entry.cond.Wait()
}
}
// Remove the transaction from the waiters list
if len(entry.waiters) > 0 && lock.ID == entry.waiters[0].ID {
entry.waiters = entry.waiters[1:]
entry.cond.Broadcast()
}
}
entry.activeLockOwnerCount++
// Otherwise, grant the lock
entry.lockType = lockType
glog.V(4).Infof("ActiveLock %d %s locked %+v type=%v with waiters %d active %d.\n", lock.ID, lock.intention, key, lockType, len(entry.waiters), entry.activeLockOwnerCount)
if len(entry.waiters) > 0 {
for _, waiter := range entry.waiters {
fmt.Printf(" %d", waiter.ID)
}
fmt.Printf("\n")
}
entry.mu.Unlock()
return lock
}
func (lt *LockTable[T]) ReleaseLock(key T, lock *ActiveLock) {
lt.mu.Lock()
defer lt.mu.Unlock()
entry, exists := lt.locks[key]
if !exists {
return
}
entry.mu.Lock()
defer entry.mu.Unlock()
// Remove the transaction from the waiters list
for i, waiter := range entry.waiters {
if waiter == lock {
waiter.isDeleted = true
entry.waiters = append(entry.waiters[:i], entry.waiters[i+1:]...)
break
}
}
// If there are no waiters, release the lock
if len(entry.waiters) == 0 {
delete(lt.locks, key)
}
glog.V(4).Infof("ActiveLock %d %s unlocked %+v type=%v with waiters %d active %d.\n", lock.ID, lock.intention, key, entry.lockType, len(entry.waiters), entry.activeLockOwnerCount)
if len(entry.waiters) > 0 {
for _, waiter := range entry.waiters {
fmt.Printf(" %d", waiter.ID)
}
fmt.Printf("\n")
}
entry.activeLockOwnerCount--
// Notify the next waiter
entry.cond.Broadcast()
}
func main() {
}
|
