Allow a token to be valid only when created by the allocator

src/XenoAtom.Allocators.Tests/BasicTests.cs

@@ -1,4 +1,5 @@
 using System.Globalization;
+using System.Runtime.CompilerServices;
 using System.Text;
 
 namespace XenoAtom.Allocators.Tests;
@@ -10,7 +11,22 @@ public partial class BasicTests
     public static MemoryAddress BaseAddress => 0xFE00_1200_0000_0000;
 
     public static MemorySize BaseChunkSize => 65536;
+
+    [TestMethod]
+    public void TestToken()
+    {
+        var token = new TlsfAllocationToken();
+        Assert.IsFalse(token.IsValid);
 
+        token = new TlsfAllocationToken(0);
+        Assert.IsTrue(token.IsValid);
+        Assert.AreEqual(0, token.BlockIndex);
+
+        token = new TlsfAllocationToken(1);
+        Assert.IsTrue(token.IsValid);
+        Assert.AreEqual(1, token.BlockIndex);
+    }
+
     [TestMethod]
     public async Task TestAllocate1()
     {

src/XenoAtom.Allocators/TlsfAllocationToken.cs

@@ -2,20 +2,60 @@
 // Licensed under the BSD-Clause 2 license.
 // See license.txt file in the project root for full license information.
 
+using System;
+using System.Runtime.CompilerServices;
+
 namespace XenoAtom.Allocators;
 
 /// <summary>
 /// A token representing an allocation from a <see cref="TlsfAllocator"/> returned by <see cref="TlsfAllocation.Token"/>.
 /// </summary>
-public readonly record struct TlsfAllocationToken
+public readonly struct TlsfAllocationToken : IEquatable<TlsfAllocationToken>
 {
-    internal TlsfAllocationToken(uint blockIndex)
+    private readonly int _blockIndex;
+
+    internal TlsfAllocationToken(int blockIndex)
+    {
+        // Block index is stored with the operator ~ to be able to detect if the token is valid or not.
+        _blockIndex = ~blockIndex;
+    }
+
+    /// <summary>
+    /// Returns true if this token is valid.
+    /// </summary>
+    public bool IsValid
     {
-        BlockIndex = blockIndex;
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => _blockIndex < 0;
     }
 
-    internal readonly uint BlockIndex;
+    internal int BlockIndex => ~_blockIndex;
 
     /// <inheritdoc />
     public override string ToString() => $"TlsfAllocationToken({BlockIndex})";
+
+    public bool Equals(TlsfAllocationToken other)
+    {
+        return _blockIndex == other._blockIndex;
+    }
+
+    public override bool Equals(object? obj)
+    {
+        return obj is TlsfAllocationToken other && Equals(other);
+    }
+
+    public override int GetHashCode()
+    {
+        return _blockIndex;
+    }
+
+    public static bool operator ==(TlsfAllocationToken left, TlsfAllocationToken right)
+    {
+        return left.Equals(right);
+    }
+
+    public static bool operator !=(TlsfAllocationToken left, TlsfAllocationToken right)
+    {
+        return !left.Equals(right);
+    }
 }

src/XenoAtom.Allocators/TlsfAllocator.cs

@@ -170,7 +170,7 @@ public bool TryAllocate(MemorySize size, out TlsfAllocation allocation)
                 InsertBlockIntoFreeList(ref freeBlock, freeBlockIndex, newFirstLevelIndex, newSecondLevelIndex);
             }
 
-            allocation = new TlsfAllocation(new((uint)usedBlockIndex), chunk.Info.Id, (ulong)chunk.Info.BaseAddress + offsetIntoChunk, size);
+            allocation = new TlsfAllocation(new(usedBlockIndex), chunk.Info.Id, (ulong)chunk.Info.BaseAddress + offsetIntoChunk, size);
         }
         else
         {
@@ -184,7 +184,7 @@ public bool TryAllocate(MemorySize size, out TlsfAllocation allocation)
             chunk.FreeBlockCount--;
             Debug.Assert(chunk.FreeBlockCount >= 0);
 
-            allocation = new TlsfAllocation(new((uint)freeBlockIndex), chunk.Info.Id, (ulong)chunk.Info.BaseAddress + offsetIntoChunk, size);
+            allocation = new TlsfAllocation(new(freeBlockIndex), chunk.Info.Id, (ulong)chunk.Info.BaseAddress + offsetIntoChunk, size);
         }
 
         return true;

src/XenoAtom.Allocators/XenoAtom.Allocators.csproj

@@ -32,6 +32,7 @@
   </ItemGroup>
 
   <ItemGroup>
+    <InternalsVisibleTo Include="$(AssemblyName).Tests" />
     <PackageReference Include="MinVer" Version="5.0.0">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>