add lock table to ensure ordered locks

1 files changed, 146 insertions, 0 deletions

diff --git a/weed/util/lock_table.go b/weed/util/lock_table.go
new file mode 100644
index 000000000..32d98bea3
--- /dev/null
+++ b/weed/util/lock_table.go
@@ -0,0 +1,146 @@
+package util
+
+import (
+	"fmt"
+	"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(&lt.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 {
+		fmt.Printf("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
+	fmt.Printf("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)
+	}
+
+	fmt.Printf("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() {
+
+}