Convert EnterExitWrapper to a readonly ref struct, this should be a speedup in all cases. Will need to experiment to see if this mean the try/finally from #3296 can be avoided

Author: CasualPokePlayer

src/BizHawk.Client.EmuHawk/RetroAchievements/RetroAchievements.Memory.cs

@@ -79,15 +79,15 @@ protected virtual int FixAddr(int addr)
 
 			protected virtual byte ReadMem(int addr)
 			{
-				using (MemGuard?.EnterExit())
+				using (MemGuard.EnterExit())
 				{
 					return _domain.PeekByte(FixAddr(addr) ^ _addressMangler);
 				}
 			}
 
 			protected virtual void WriteMem(int addr, byte val)
 			{
-				using (MemGuard?.EnterExit())
+				using (MemGuard.EnterExit())
 				{
 					_domain.PokeByte(FixAddr(addr) ^ _addressMangler, val);
 				}
@@ -102,7 +102,7 @@ protected virtual int ReadMemBlock(int addr, IntPtr buffer, int bytes)
 					return 0;
 				}
 
-				using (MemGuard?.EnterExit())
+				using (MemGuard.EnterExit())
 				{
 					var end = Math.Min(addr + bytes, _domainAddrStart + BankSize);
 					var length = end - addr;
@@ -191,7 +191,7 @@ protected override int ReadMemBlock(int addr, IntPtr buffer, int bytes)
 					return 0;
 				}
 
-				using (MemGuard?.EnterExit())
+				using (MemGuard.EnterExit())
 				{
 					var end = Math.Min(addr + bytes, BankSize);
 					var length = end - addr;
@@ -236,7 +236,7 @@ private byte ReadVRAMPacked(int addr)
 
 			protected override byte ReadMem(int addr)
 			{
-				using (MemGuard?.EnterExit())
+				using (MemGuard.EnterExit())
 				{
 					if (addr < 0x40)
 					{
@@ -251,7 +251,7 @@ protected override byte ReadMem(int addr)
 
 			protected override void WriteMem(int addr, byte val)
 			{
-				using (MemGuard?.EnterExit())
+				using (MemGuard.EnterExit())
 				{
 					if (addr < 0x40)
 					{
@@ -275,7 +275,7 @@ protected override int ReadMemBlock(int addr, IntPtr buffer, int bytes)
 					return 0;
 				}
 
-				using (MemGuard?.EnterExit())
+				using (MemGuard.EnterExit())
 				{
 					var regs = _debuggable.GetCpuFlagsAndRegisters();
 					var end = Math.Min(addr + bytes, BankSize);

src/BizHawk.Common/IMonitor.cs

@@ -11,32 +11,22 @@ public interface IMonitor
 
 	public static class MonitorExtensions
 	{
-		public static IDisposable EnterExit(this IMonitor m)
-		{
-			var ret = new EnterExitWrapper(m);
-			m.Enter();
-			return ret;
-		}
+		public static EnterExitWrapper EnterExit(this IMonitor m)
+			=> new(m);
 
-		private class EnterExitWrapper : IDisposable
+		public readonly ref struct EnterExitWrapper
 		{
-			private readonly IMonitor _m;
+			// yes, this can be null
+			private readonly IMonitor? _m;
 
-			private bool _disposed;
-
-			public EnterExitWrapper(IMonitor m)
-			{
-				_m = m;
+			public EnterExitWrapper(IMonitor? m)
+			{
+				_m = m;
+				_m?.Enter();
 			}
 
 			public void Dispose()
-			{
-				if (!_disposed)
-				{
-					_m.Exit();
-					_disposed = true;
-				}
-			}
+				=> _m?.Exit();
 		}
 	}
 }