Track running backup count via BackupTracker

This avoids an unnecessary apiserver List call when
the backup reconciler is already at capacity.

Signed-off-by: Scott Seago <sseago@redhat.com>

pkg/controller/backup_tracker.go

@@ -25,45 +25,90 @@ import (
 
 // BackupTracker keeps track of in-progress backups.
 type BackupTracker interface {
+	// Add informs the tracker that a backup is ReadyToStart.
+	AddReadyToStart(ns, name string)
 	// Add informs the tracker that a backup is in progress.
 	Add(ns, name string)
-	// Delete informs the tracker that a backup is no longer in progress.
+	// Add informs the tracker that a backup has moved beyond InProgress
+	AddPostProcessing(ns, name string)
+	// Delete informs the tracker that a backup has reached a terminal state.
 	Delete(ns, name string)
-	// Contains returns true if the tracker is tracking the backup.
+	// Contains returns true if backup is InProgress or post-InProgress
 	Contains(ns, name string) bool
+	// RunningCount returns the number of backups which are ReadyToStart or InProgress
+	RunningCount() int
 }
 
 type backupTracker struct {
-	lock    sync.RWMutex
-	backups sets.Set[string]
+	lock                sync.RWMutex
+	readyToStartBackups sets.Set[string]
+	inProgressBackups   sets.Set[string]
+	postProgressBackups sets.Set[string]
 }
 
 // NewBackupTracker returns a new BackupTracker.
 func NewBackupTracker() BackupTracker {
 	return &backupTracker{
-		backups: sets.New[string](),
+		readyToStartBackups: sets.New[string](),
+		inProgressBackups:   sets.New[string](),
+		postProgressBackups: sets.New[string](),
 	}
 }
 
+func (bt *backupTracker) AddReadyToStart(ns, name string) {
+	bt.lock.Lock()
+	defer bt.lock.Unlock()
+
+	bt.readyToStartBackups.Insert(backupTrackerKey(ns, name))
+}
+
 func (bt *backupTracker) Add(ns, name string) {
 	bt.lock.Lock()
 	defer bt.lock.Unlock()
 
-	bt.backups.Insert(backupTrackerKey(ns, name))
+	key := backupTrackerKey(ns, name)
+	bt.readyToStartBackups.Delete(key)
+	bt.inProgressBackups.Insert(key)
+}
+
+func (bt *backupTracker) AddPostProcessing(ns, name string) {
+	bt.lock.Lock()
+	defer bt.lock.Unlock()
+
+	key := backupTrackerKey(ns, name)
+	bt.readyToStartBackups.Delete(key)
+	bt.inProgressBackups.Delete(key)
+	bt.postProgressBackups.Insert(key)
 }
 
 func (bt *backupTracker) Delete(ns, name string) {
 	bt.lock.Lock()
 	defer bt.lock.Unlock()
 
-	bt.backups.Delete(backupTrackerKey(ns, name))
+	key := backupTrackerKey(ns, name)
+	bt.readyToStartBackups.Delete(key)
+	bt.inProgressBackups.Delete(key)
+	bt.postProgressBackups.Delete(key)
 }
 
+// Contains returns true if backup is InProgress or post-InProgress
+// ignores ReadyToStart, since this is used to determine whether
+// a backup is in progress and thus not able to be deleted now.
 func (bt *backupTracker) Contains(ns, name string) bool {
 	bt.lock.RLock()
 	defer bt.lock.RUnlock()
 
-	return bt.backups.Has(backupTrackerKey(ns, name))
+	key := backupTrackerKey(ns, name)
+	return bt.inProgressBackups.Has(key) || bt.postProgressBackups.Has(key)
+}
+
+// RunningCount returns the number of backups which are ReadyToStart or InProgress
+// used by queue controller to determine whether a new backup can be started.
+func (bt *backupTracker) RunningCount() int {
+	bt.lock.RLock()
+	defer bt.lock.RUnlock()
+
+	return bt.inProgressBackups.Len() + bt.readyToStartBackups.Len()
 }
 
 func backupTrackerKey(ns, name string) string {