[Mono.Android] Guard GREF/WREF logging P/Invokes behind Logger.LogGlobalRef check

The AndroidObjectReferenceManager overrides for CreateGlobalReference,
DeleteGlobalReference, CreateWeakGlobalReference, and
DeleteWeakGlobalReference were unconditionally calling native logging
P/Invokes on every invocation, even when GREF logging was disabled.

While the native side does an early return when LOG_GREF is off, the
managed-to-native transition itself has significant overhead that adds
up in tight loops (e.g. GC bridge processing with thousands of refs).

Changes:
- Guard all 4 logging P/Invoke calls behind `if (Logger.LogGlobalRef)`
  early-return checks, matching the existing local ref pattern
- Add managed `_grefc` and `_weak_grefc` counters using Interlocked
  to replace the native counter P/Invokes
- Keep the gref_gc_threshold full-GC trigger working unconditionally
- Switch GlobalReferenceCount/WeakGlobalReferenceCount properties to
  read from managed counters via Volatile.Read

Performance (physical device, CoreCLR, Release, 3740 objects):
- Bridge cleanup: 385ms → 4ms (~100x improvement)
- Per-object NewGlobalRef overhead: ~7000µs → ~0µs

Author: simonrozsival

src/Mono.Android/Android.Runtime/AndroidRuntime.cs

@@ -103,12 +103,15 @@ public AndroidRuntimeOptions (IntPtr jnienv,
 	}
 
 	internal class AndroidObjectReferenceManager : JniRuntime.JniObjectReferenceManager {
+		static int _grefc;
+		static int _weak_grefc;
+
 		public override int GlobalReferenceCount {
-			get {return RuntimeNativeMethods._monodroid_gref_get ();}
+			get {return Volatile.Read (ref _grefc);}
 		}
 
 		public override int WeakGlobalReferenceCount {
-			get {return RuntimeNativeMethods._monodroid_weak_gref_get ();}
+			get {return Volatile.Read (ref _weak_grefc);}
 		}
 
 		public override JniObjectReference CreateLocalReference (JniObjectReference value, ref int localReferenceCount)
@@ -176,20 +179,24 @@ public override void WriteGlobalReferenceLine (string format, params object?[] a
 
 		public override JniObjectReference CreateGlobalReference (JniObjectReference value)
 		{
-			var r     = base.CreateGlobalReference (value);
+			var r  = base.CreateGlobalReference (value);
+			int gc = Interlocked.Increment (ref _grefc);
 
-			var log		= Logger.LogGlobalRef;
-			var ctype	= log ? GetObjectRefType (value.Type) : (byte) '*';
-			var ntype	= log ? GetObjectRefType (r.Type) : (byte) '*';
-			var tname = log ? Thread.CurrentThread.Name : null;
-			var tid   = log ? Thread.CurrentThread.ManagedThreadId : 0;
-			var from  = log ? new StringBuilder (new StackTrace (true).ToString ()) : null;
-			int gc 		= RuntimeNativeMethods._monodroid_gref_log_new (value.Handle, ctype, r.Handle, ntype, tname, tid, from, 1);
 			if (gc >= JNIEnvInit.gref_gc_threshold) {
 				Logger.Log (LogLevel.Warn, "monodroid-gc", gc + " outstanding GREFs. Performing a full GC!");
 				System.GC.Collect ();
 			}
 
+			if (!Logger.LogGlobalRef)
+				return r;
+
+			var ctype = GetObjectRefType (value.Type);
+			var ntype = GetObjectRefType (r.Type);
+			var tname = Thread.CurrentThread.Name;
+			var tid   = Thread.CurrentThread.ManagedThreadId;
+			var from  = new StringBuilder (new StackTrace (true).ToString ());
+			RuntimeNativeMethods._monodroid_gref_log_new (value.Handle, ctype, r.Handle, ntype, tname, tid, from, 1);
+
 			return r;
 		}
 
@@ -206,11 +213,17 @@ static byte GetObjectRefType (JniObjectReferenceType type)
 
 		public override void DeleteGlobalReference (ref JniObjectReference value)
 		{
-			var log		= Logger.LogGlobalRef;
-			var ctype	= log ? GetObjectRefType (value.Type) : (byte) '*';
-			var tname = log ? Thread.CurrentThread.Name : null;
-			var tid   = log ? Thread.CurrentThread.ManagedThreadId : 0;
-			var from  = log ? new StringBuilder (new StackTrace (true).ToString ()) : null;
+			Interlocked.Decrement (ref _grefc);
+
+			if (!Logger.LogGlobalRef) {
+				base.DeleteGlobalReference (ref value);
+				return;
+			}
+
+			var ctype = GetObjectRefType (value.Type);
+			var tname = Thread.CurrentThread.Name;
+			var tid   = Thread.CurrentThread.ManagedThreadId;
+			var from  = new StringBuilder (new StackTrace (true).ToString ());
 			RuntimeNativeMethods._monodroid_gref_log_delete (value.Handle, ctype, tname, tid, from, 1);
 
 			base.DeleteGlobalReference (ref value);
@@ -219,25 +232,34 @@ public override void DeleteGlobalReference (ref JniObjectReference value)
 		public override JniObjectReference CreateWeakGlobalReference (JniObjectReference value)
 		{
 			var r = base.CreateWeakGlobalReference (value);
+			Interlocked.Increment (ref _weak_grefc);
+
+			if (!Logger.LogGlobalRef)
+				return r;
 
-			var log		= Logger.LogGlobalRef;
-			var ctype	= log ? GetObjectRefType (value.Type) : (byte) '*';
-			var ntype	= log ? GetObjectRefType (r.Type) : (byte) '*';
-			var tname = log ? Thread.CurrentThread.Name : null;
-			var tid   = log ? Thread.CurrentThread.ManagedThreadId : 0;
-			var from  = log ? new StringBuilder (new StackTrace (true).ToString ()) : null;
+			var ctype = GetObjectRefType (value.Type);
+			var ntype = GetObjectRefType (r.Type);
+			var tname = Thread.CurrentThread.Name;
+			var tid   = Thread.CurrentThread.ManagedThreadId;
+			var from  = new StringBuilder (new StackTrace (true).ToString ());
 			RuntimeNativeMethods._monodroid_weak_gref_new (value.Handle, ctype, r.Handle, ntype, tname, tid, from, 1);
 
 			return r;
 		}
 
 		public override void DeleteWeakGlobalReference (ref JniObjectReference value)
 		{
-			var log		= Logger.LogGlobalRef;
-			var ctype	= log ? GetObjectRefType (value.Type) : (byte) '*';
-			var tname = log ? Thread.CurrentThread.Name : null;
-			var tid   = log ? Thread.CurrentThread.ManagedThreadId : 0;
-			var from  = log ? new StringBuilder (new StackTrace (true).ToString ()) : null;
+			Interlocked.Decrement (ref _weak_grefc);
+
+			if (!Logger.LogGlobalRef) {
+				base.DeleteWeakGlobalReference (ref value);
+				return;
+			}
+
+			var ctype = GetObjectRefType (value.Type);
+			var tname = Thread.CurrentThread.Name;
+			var tid   = Thread.CurrentThread.ManagedThreadId;
+			var from  = new StringBuilder (new StackTrace (true).ToString ());
 			RuntimeNativeMethods._monodroid_weak_gref_delete (value.Handle, ctype, tname, tid, from, 1);
 
 			base.DeleteWeakGlobalReference (ref value);