Add statistic for count of alive WorkingBeatmaps

osu.Game/Beatmaps/WorkingBeatmap.cs

@@ -13,6 +13,7 @@
 using System.Threading;
 using System.Threading.Tasks;
 using osu.Framework.Audio;
+using osu.Framework.Statistics;
 using osu.Game.IO.Serialization;
 using osu.Game.Rulesets;
 using osu.Game.Rulesets.Objects;
@@ -32,6 +33,8 @@ public abstract class WorkingBeatmap : IDisposable
 
         protected AudioManager AudioManager { get; }
 
+        private static readonly GlobalStatistic<int> total_count = GlobalStatistics.Get<int>(nameof(Beatmaps), $"Total {nameof(WorkingBeatmap)}s");
+
         protected WorkingBeatmap(BeatmapInfo beatmapInfo, AudioManager audioManager)
         {
             AudioManager = audioManager;
@@ -44,6 +47,8 @@ protected WorkingBeatmap(BeatmapInfo beatmapInfo, AudioManager audioManager)
             waveform = new RecyclableLazy<Waveform>(GetWaveform);
             storyboard = new RecyclableLazy<Storyboard>(GetStoryboard);
             skin = new RecyclableLazy<Skin>(GetSkin);
+
+            total_count.Value++;
         }
 
         protected virtual Track GetVirtualTrack()
@@ -227,8 +232,15 @@ public void Dispose()
             GC.SuppressFinalize(this);
         }
 
+        private bool isDisposed;
+
         protected virtual void Dispose(bool isDisposing)
         {
+            if (isDisposed)
+                return;
+
+            isDisposed = true;
+
             // recycling logic is not here for the time being, as components which use
             // retrieved objects from WorkingBeatmap may not hold a reference to the WorkingBeatmap itself.
             // this should be fine as each retrieved component do have their own finalizers.
@@ -236,6 +248,8 @@ protected virtual void Dispose(bool isDisposing)
             // cancelling the beatmap load is safe for now since the retrieval is a synchronous
             // operation. if we add an async retrieval method this may need to be reconsidered.
             beatmapCancellation.Cancel();
+
+            total_count.Value--;
         }
 
         ~WorkingBeatmap()