admin: add plugin lock coordination

weed/admin/dash/admin_lock_manager.go

@@ -0,0 +1,87 @@
+package dash
+
+import (
+	"sync"
+
+	"github.com/seaweedfs/seaweedfs/weed/wdclient"
+	"github.com/seaweedfs/seaweedfs/weed/wdclient/exclusive_locks"
+)
+
+const (
+	adminLockName       = "shell"
+	adminLockClientName = "admin-plugin"
+)
+
+// AdminLockManager coordinates exclusive admin locks with reference counting.
+// It is safe for concurrent use.
+type AdminLockManager struct {
+	locker     *exclusive_locks.ExclusiveLocker
+	clientName string
+
+	mu        sync.Mutex
+	cond      *sync.Cond
+	acquiring bool
+	holdCount int
+}
+
+func NewAdminLockManager(masterClient *wdclient.MasterClient, clientName string) *AdminLockManager {
+	if masterClient == nil {
+		return nil
+	}
+	if clientName == "" {
+		clientName = adminLockClientName
+	}
+	manager := &AdminLockManager{
+		locker:     exclusive_locks.NewExclusiveLocker(masterClient, adminLockName),
+		clientName: clientName,
+	}
+	manager.cond = sync.NewCond(&manager.mu)
+	return manager
+}
+
+func (m *AdminLockManager) Acquire(reason string) (func(), error) {
+	if m == nil || m.locker == nil {
+		return func() {}, nil
+	}
+
+	m.mu.Lock()
+	if reason != "" {
+		m.locker.SetMessage(reason)
+	}
+	for m.acquiring {
+		m.cond.Wait()
+	}
+	if m.holdCount == 0 {
+		m.acquiring = true
+		m.mu.Unlock()
+		m.locker.RequestLock(m.clientName)
+		m.mu.Lock()
+		m.acquiring = false
+		m.holdCount = 1
+		m.cond.Broadcast()
+		m.mu.Unlock()
+		return m.Release, nil
+	}
+	m.holdCount++
+	m.mu.Unlock()
+	return m.Release, nil
+}
+
+func (m *AdminLockManager) Release() {
+	if m == nil || m.locker == nil {
+		return
+	}
+
+	m.mu.Lock()
+	if m.holdCount <= 0 {
+		m.mu.Unlock()
+		return
+	}
+	m.holdCount--
+	shouldRelease := m.holdCount == 0
+	m.mu.Unlock()
+
+	if shouldRelease {
+		m.locker.ReleaseLock()
+	}
+}