Add accumulative allocation tracking to allocators

src/ImageSharp/Memory/Allocators/MemoryAllocator.cs

@@ -12,6 +12,8 @@ namespace SixLabors.ImageSharp.Memory;
 public abstract class MemoryAllocator
 {
     private const int OneGigabyte = 1 << 30;
+    private long accumulativeAllocatedBytes;
+    private int trackingSuppressionCount;
 
     /// <summary>
     /// Gets the default platform-specific global <see cref="MemoryAllocator"/> instance that
@@ -23,9 +25,41 @@ public abstract class MemoryAllocator
     /// </summary>
     public static MemoryAllocator Default { get; } = Create();
 
-    internal long MemoryGroupAllocationLimitBytes { get; private set; } = Environment.Is64BitProcess ? 4L * OneGigabyte : OneGigabyte;
+    /// <summary>
+    /// Gets the maximum number of bytes that can be allocated by a memory group.
+    /// </summary>
+    /// <remarks>
+    /// The allocation limit is determined by the process architecture: 4 GB for 64-bit processes and
+    /// 1 GB for 32-bit processes.
+    /// </remarks>
+    internal long MemoryGroupAllocationLimitBytes { get; private protected set; } = Environment.Is64BitProcess ? 4L * OneGigabyte : OneGigabyte;
+
+    /// <summary>
+    /// Gets the maximum allowed total allocation size, in bytes, for the current process.
+    /// </summary>
+    /// <remarks>
+    /// The allocation limit is determined based on the process architecture. For 64-bit processes,
+    /// the limit is higher than for 32-bit processes.
+    /// </remarks>
+    internal long AccumulativeAllocationLimitBytes { get; private protected set; } = Environment.Is64BitProcess ? 8L * OneGigabyte : 2L * OneGigabyte;
 
-    internal int SingleBufferAllocationLimitBytes { get; private set; } = OneGigabyte;
+    /// <summary>
+    /// Gets the maximum size, in bytes, that can be allocated for a single buffer.
+    /// </summary>
+    /// <remarks>
+    /// The single buffer allocation limit is set to 1 GB by default.
+    /// </remarks>
+    internal int SingleBufferAllocationLimitBytes { get; private protected set; } = OneGigabyte;
+
+    /// <summary>
+    /// Gets a value indicating whether change tracking is currently suppressed for this instance.
+    /// </summary>
+    /// <remarks>
+    /// When change tracking is suppressed, modifications to the object will not be recorded or
+    /// trigger change notifications. This property is used internally to temporarily disable tracking during
+    /// batch updates or initialization.
+    /// </remarks>
+    private bool IsTrackingSuppressed => Volatile.Read(ref this.trackingSuppressionCount) > 0;
 
     /// <summary>
     /// Gets the length of the largest contiguous buffer that can be handled by this allocator instance in bytes.
@@ -53,6 +87,11 @@ public abstract class MemoryAllocator
             allocator.SingleBufferAllocationLimitBytes = (int)Math.Min(allocator.SingleBufferAllocationLimitBytes, allocator.MemoryGroupAllocationLimitBytes);
         }
 
+        if (options.AccumulativeAllocationLimitMegabytes.HasValue)
+        {
+            allocator.AccumulativeAllocationLimitBytes = options.AccumulativeAllocationLimitMegabytes.Value * 1024L * 1024L;
+        }
+
         return allocator;
     }
 
@@ -72,6 +111,10 @@ public abstract class MemoryAllocator
     /// Releases all retained resources not being in use.
     /// Eg: by resetting array pools and letting GC to free the arrays.
     /// </summary>
+    /// <remarks>
+    /// This does not dispose active allocations; callers are responsible for disposing all
+    /// <see cref="IMemoryOwner{T}"/> instances to release memory.
+    /// </remarks>
     public virtual void ReleaseRetainedResources()
     {
     }
@@ -102,11 +145,137 @@ public abstract class MemoryAllocator
             InvalidMemoryOperationException.ThrowAllocationOverLimitException(totalLengthInBytes, this.MemoryGroupAllocationLimitBytes);
         }
 
-        // Cast to long is safe because we already checked that the total length is within the limit.
-        return this.AllocateGroupCore<T>(totalLength, (long)totalLengthInBytes, bufferAlignment, options);
+        long totalLengthInBytesLong = (long)totalLengthInBytes;
+        this.ReserveAllocation(totalLengthInBytesLong);
+
+        using (this.SuppressTracking())
+        {
+            try
+            {
+                MemoryGroup<T> group = this.AllocateGroupCore<T>(totalLength, totalLengthInBytesLong, bufferAlignment, options);
+                group.SetAllocationTracking(this, totalLengthInBytesLong);
+                return group;
+            }
+            catch
+            {
+                this.ReleaseAccumulatedBytes(totalLengthInBytesLong);
+                throw;
+            }
+        }
     }
 
     internal virtual MemoryGroup<T> AllocateGroupCore<T>(long totalLengthInElements, long totalLengthInBytes, int bufferAlignment, AllocationOptions options)
         where T : struct
         => MemoryGroup<T>.Allocate(this, totalLengthInElements, bufferAlignment, options);
+
+    /// <summary>
+    /// Tracks the allocation of an <see cref="IMemoryOwner{T}" /> instance after reserving bytes.
+    /// </summary>
+    /// <typeparam name="T">Type of the data stored in the buffer.</typeparam>
+    /// <param name="owner">The allocation to track.</param>
+    /// <param name="lengthInBytes">The allocation size in bytes.</param>
+    /// <returns>The tracked allocation.</returns>
+    protected IMemoryOwner<T> TrackAllocation<T>(IMemoryOwner<T> owner, ulong lengthInBytes)
+        where T : struct
+    {
+        if (this.IsTrackingSuppressed || lengthInBytes == 0)
+        {
+            return owner;
+        }
+
+        return new TrackingMemoryOwner<T>(owner, this, (long)lengthInBytes);
+    }
+
+    /// <summary>
+    /// Reserves accumulative allocation bytes before creating the underlying buffer.
+    /// </summary>
+    /// <param name="lengthInBytes">The number of bytes to reserve.</param>
+    protected void ReserveAllocation(long lengthInBytes)
+    {
+        if (this.IsTrackingSuppressed || lengthInBytes <= 0)
+        {
+            return;
+        }
+
+        long total = Interlocked.Add(ref this.accumulativeAllocatedBytes, lengthInBytes);
+        if (total > this.AccumulativeAllocationLimitBytes)
+        {
+            _ = Interlocked.Add(ref this.accumulativeAllocatedBytes, -lengthInBytes);
+            InvalidMemoryOperationException.ThrowAllocationOverLimitException((ulong)lengthInBytes, this.AccumulativeAllocationLimitBytes);
+        }
+    }
+
+    /// <summary>
+    /// Releases accumulative allocation bytes previously tracked by this allocator.
+    /// </summary>
+    /// <param name="lengthInBytes">The number of bytes to release.</param>
+    internal void ReleaseAccumulatedBytes(long lengthInBytes)
+    {
+        if (lengthInBytes <= 0)
+        {
+            return;
+        }
+
+        _ = Interlocked.Add(ref this.accumulativeAllocatedBytes, -lengthInBytes);
+    }
+
+    /// <summary>
+    /// Suppresses accumulative allocation tracking for the lifetime of the returned scope.
+    /// </summary>
+    /// <returns>An <see cref="IDisposable"/> that restores tracking when disposed.</returns>
+    internal IDisposable SuppressTracking() => new TrackingSuppressionScope(this);
+
+    /// <summary>
+    /// Temporarily suppresses accumulative allocation tracking within a scope.
+    /// </summary>
+    private sealed class TrackingSuppressionScope : IDisposable
+    {
+        private MemoryAllocator? allocator;
+
+        public TrackingSuppressionScope(MemoryAllocator allocator)
+        {
+            this.allocator = allocator;
+            _ = Interlocked.Increment(ref allocator.trackingSuppressionCount);
+        }
+
+        public void Dispose()
+        {
+            if (this.allocator != null)
+            {
+                _ = Interlocked.Decrement(ref this.allocator.trackingSuppressionCount);
+                this.allocator = null;
+            }
+        }
+    }
+
+    /// <summary>
+    /// Wraps an <see cref="IMemoryOwner{T}"/> to release accumulative tracking on dispose.
+    /// </summary>
+    private sealed class TrackingMemoryOwner<T> : IMemoryOwner<T>
+        where T : struct
+    {
+        private IMemoryOwner<T>? owner;
+        private readonly MemoryAllocator allocator;
+        private readonly long lengthInBytes;
+
+        public TrackingMemoryOwner(IMemoryOwner<T> owner, MemoryAllocator allocator, long lengthInBytes)
+        {
+            this.owner = owner;
+            this.allocator = allocator;
+            this.lengthInBytes = lengthInBytes;
+        }
+
+        public Memory<T> Memory => this.owner?.Memory ?? Memory<T>.Empty;
+
+        public void Dispose()
+        {
+            // Ensure only one caller disposes the inner owner and releases the reservation.
+            IMemoryOwner<T>? inner = Interlocked.Exchange(ref this.owner, null);
+            if (inner != null)
+            {
+                inner.Dispose();
+                this.allocator.ReleaseAccumulatedBytes(this.lengthInBytes);
+            }
+        }
+    }
 }

src/ImageSharp/Memory/Allocators/MemoryAllocatorOptions.cs

@@ -10,6 +10,7 @@ public struct MemoryAllocatorOptions
 {
     private int? maximumPoolSizeMegabytes;
     private int? allocationLimitMegabytes;
+    private int? accumulativeAllocationLimitMegabytes;
 
     /// <summary>
     /// Gets or sets a value defining the maximum size of the <see cref="MemoryAllocator"/>'s internal memory pool
@@ -17,7 +18,7 @@ public struct MemoryAllocatorOptions
     /// </summary>
     public int? MaximumPoolSizeMegabytes
     {
-        get => this.maximumPoolSizeMegabytes;
+        readonly get => this.maximumPoolSizeMegabytes;
         set
         {
             if (value.HasValue)
@@ -35,7 +36,7 @@ public struct MemoryAllocatorOptions
     /// </summary>
     public int? AllocationLimitMegabytes
     {
-        get => this.allocationLimitMegabytes;
+        readonly get => this.allocationLimitMegabytes;
         set
         {
             if (value.HasValue)
@@ -46,4 +47,29 @@ public struct MemoryAllocatorOptions
             this.allocationLimitMegabytes = value;
         }
     }
+
+    /// <summary>
+    /// Gets or sets a value defining the maximum total size that can be allocated by the allocator in Megabytes.
+    /// <see langword="null"/> means platform default: 2GB on 32-bit processes, 8GB on 64-bit processes.
+    /// </summary>
+    public int? AccumulativeAllocationLimitMegabytes
+    {
+        readonly get => this.accumulativeAllocationLimitMegabytes;
+        set
+        {
+            if (value.HasValue)
+            {
+                Guard.MustBeGreaterThan(value.Value, 0, nameof(this.AccumulativeAllocationLimitMegabytes));
+                if (this.AllocationLimitMegabytes.HasValue)
+                {
+                    Guard.MustBeGreaterThanOrEqualTo(
+                        value.Value,
+                        this.AllocationLimitMegabytes.Value,
+                        nameof(this.AccumulativeAllocationLimitMegabytes));
+                }
+            }
+
+            this.accumulativeAllocationLimitMegabytes = value;
+        }
+    }
 }

src/ImageSharp/Memory/Allocators/SimpleGcMemoryAllocator.cs

@@ -12,6 +12,32 @@ namespace SixLabors.ImageSharp.Memory;
 /// </summary>
 public sealed class SimpleGcMemoryAllocator : MemoryAllocator
 {
+    /// <summary>
+    /// Initializes a new instance of the <see cref="SimpleGcMemoryAllocator"/> class with default limits.
+    /// </summary>
+    public SimpleGcMemoryAllocator()
+        : this(default)
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="SimpleGcMemoryAllocator"/> class with custom limits.
+    /// </summary>
+    /// <param name="options">The <see cref="MemoryAllocatorOptions"/> to apply.</param>
+    public SimpleGcMemoryAllocator(MemoryAllocatorOptions options)
+    {
+        if (options.AllocationLimitMegabytes.HasValue)
+        {
+            this.MemoryGroupAllocationLimitBytes = options.AllocationLimitMegabytes.Value * 1024L * 1024L;
+            this.SingleBufferAllocationLimitBytes = (int)Math.Min(this.SingleBufferAllocationLimitBytes, this.MemoryGroupAllocationLimitBytes);
+        }
+
+        if (options.AccumulativeAllocationLimitMegabytes.HasValue)
+        {
+            this.AccumulativeAllocationLimitBytes = options.AccumulativeAllocationLimitMegabytes.Value * 1024L * 1024L;
+        }
+    }
+
     /// <inheritdoc />
     protected internal override int GetBufferCapacityInBytes() => int.MaxValue;
 
@@ -29,6 +55,18 @@ public sealed class SimpleGcMemoryAllocator : MemoryAllocator
             InvalidMemoryOperationException.ThrowAllocationOverLimitException(lengthInBytes, this.SingleBufferAllocationLimitBytes);
         }
 
-        return new BasicArrayBuffer<T>(new T[length]);
+        long lengthInBytesLong = (long)lengthInBytes;
+        this.ReserveAllocation(lengthInBytesLong);
+
+        try
+        {
+            IMemoryOwner<T> buffer = new BasicArrayBuffer<T>(new T[length]);
+            return this.TrackAllocation(buffer, lengthInBytes);
+        }
+        catch
+        {
+            this.ReleaseAccumulatedBytes(lengthInBytesLong);
+            throw;
+        }
     }
 }

src/ImageSharp/Memory/Allocators/UniformUnmanagedMemoryPoolMemoryAllocator.cs

@@ -96,13 +96,24 @@ internal sealed class UniformUnmanagedMemoryPoolMemoryAllocator : MemoryAllocato
 
         if (lengthInBytes <= (ulong)this.sharedArrayPoolThresholdInBytes)
         {
-            SharedArrayPoolBuffer<T> buffer = new(length);
-            if (options.Has(AllocationOptions.Clean))
+            long lengthInBytesLong = (long)lengthInBytes;
+            this.ReserveAllocation(lengthInBytesLong);
+
+            try
             {
-                buffer.GetSpan().Clear();
-            }
+                SharedArrayPoolBuffer<T> buffer = new(length);
+                if (options.Has(AllocationOptions.Clean))
+                {
+                    buffer.GetSpan().Clear();
+                }
 
-            return buffer;
+                return this.TrackAllocation(buffer, lengthInBytes);
+            }
+            catch
+            {
+                this.ReleaseAccumulatedBytes(lengthInBytesLong);
+                throw;
+            }
         }
 
         if (lengthInBytes <= (ulong)this.poolBufferSizeInBytes)
@@ -110,12 +121,38 @@ internal sealed class UniformUnmanagedMemoryPoolMemoryAllocator : MemoryAllocato
             UnmanagedMemoryHandle mem = this.pool.Rent();
             if (mem.IsValid)
             {
-                UnmanagedBuffer<T> buffer = this.pool.CreateGuardedBuffer<T>(mem, length, options.Has(AllocationOptions.Clean));
-                return buffer;
+                long lengthInBytesLong = (long)lengthInBytes;
+                this.ReserveAllocation(lengthInBytesLong);
+
+                try
+                {
+                    UnmanagedBuffer<T> buffer = this.pool.CreateGuardedBuffer<T>(mem, length, options.Has(AllocationOptions.Clean));
+                    return this.TrackAllocation(buffer, lengthInBytes);
+                }
+                catch
+                {
+                    this.ReleaseAccumulatedBytes(lengthInBytesLong);
+                    throw;
+                }
             }
         }
 
-        return this.nonPoolAllocator.Allocate<T>(length, options);
+        long nonPooledLengthInBytesLong = (long)lengthInBytes;
+        this.ReserveAllocation(nonPooledLengthInBytesLong);
+
+        try
+        {
+            using (this.nonPoolAllocator.SuppressTracking())
+            {
+                IMemoryOwner<T> nonPooled = this.nonPoolAllocator.Allocate<T>(length, options);
+                return this.TrackAllocation(nonPooled, lengthInBytes);
+            }
+        }
+        catch
+        {
+            this.ReleaseAccumulatedBytes(nonPooledLengthInBytesLong);
+            throw;
+        }
     }
 
     /// <inheritdoc />
@@ -148,7 +185,10 @@ internal sealed class UniformUnmanagedMemoryPoolMemoryAllocator : MemoryAllocato
             return poolGroup;
         }
 
-        return MemoryGroup<T>.Allocate(this.nonPoolAllocator, totalLengthInElements, bufferAlignment, options);
+        using (this.nonPoolAllocator.SuppressTracking())
+        {
+            return MemoryGroup<T>.Allocate(this.nonPoolAllocator, totalLengthInElements, bufferAlignment, options);
+        }
     }
 
     public override void ReleaseRetainedResources() => this.pool.Release();

src/ImageSharp/Memory/Allocators/UnmanagedMemoryAllocator.cs

@@ -2,6 +2,7 @@
 // Licensed under the Six Labors Split License.
 
 using System.Buffers;
+using System.Runtime.CompilerServices;
 using SixLabors.ImageSharp.Memory.Internals;
 
 namespace SixLabors.ImageSharp.Memory;
@@ -19,13 +20,26 @@ internal class UnmanagedMemoryAllocator : MemoryAllocator
     protected internal override int GetBufferCapacityInBytes() => this.bufferCapacityInBytes;
 
     public override IMemoryOwner<T> Allocate<T>(int length, AllocationOptions options = AllocationOptions.None)
+        where T : struct
     {
-        UnmanagedBuffer<T> buffer = UnmanagedBuffer<T>.Allocate(length);
-        if (options.Has(AllocationOptions.Clean))
+        ulong lengthInBytes = (ulong)length * (ulong)Unsafe.SizeOf<T>();
+        long lengthInBytesLong = (long)lengthInBytes;
+        this.ReserveAllocation(lengthInBytesLong);
+
+        try
         {
-            buffer.GetSpan().Clear();
-        }
+            UnmanagedBuffer<T> buffer = UnmanagedBuffer<T>.Allocate(length);
+            if (options.Has(AllocationOptions.Clean))
+            {
+                buffer.GetSpan().Clear();
+            }
 
-        return buffer;
+            return this.TrackAllocation(buffer, lengthInBytes);
+        }
+        catch
+        {
+            this.ReleaseAccumulatedBytes(lengthInBytesLong);
+            throw;
+        }
     }
 }

src/ImageSharp/Memory/DiscontiguousBuffers/IMemoryGroup{T}.cs

@@ -15,12 +15,12 @@ public interface IMemoryGroup<T> : IReadOnlyList<Memory<T>>
     /// Gets the number of elements per contiguous sub-buffer preceding the last buffer.
     /// The last buffer is allowed to be smaller.
     /// </summary>
-    int BufferLength { get; }
+    public int BufferLength { get; }
 
     /// <summary>
     /// Gets the aggregate number of elements in the group.
     /// </summary>
-    long TotalLength { get; }
+    public long TotalLength { get; }
 
     /// <summary>
     /// Gets a value indicating whether the group has been invalidated.
@@ -29,7 +29,7 @@ public interface IMemoryGroup<T> : IReadOnlyList<Memory<T>>
     /// Invalidation usually occurs when an image processor capable to alter the image dimensions replaces
     /// the image buffers internally.
     /// </remarks>
-    bool IsValid { get; }
+    public bool IsValid { get; }
 
     /// <summary>
     /// Returns a value-type implementing an allocation-free enumerator of the memory groups in the current
@@ -39,5 +39,5 @@ public interface IMemoryGroup<T> : IReadOnlyList<Memory<T>>
     /// implementation, which is still available when casting to one of the underlying interfaces.
     /// </summary>
     /// <returns>A new <see cref="MemoryGroupEnumerator{T}"/> instance mapping the current <see cref="Memory{T}"/> values in use.</returns>
-    new MemoryGroupEnumerator<T> GetEnumerator();
+    public new MemoryGroupEnumerator<T> GetEnumerator();
 }

src/ImageSharp/Memory/DiscontiguousBuffers/MemoryGroup{T}.Consumed.cs

@@ -31,23 +31,23 @@ internal abstract partial class MemoryGroup<T>
 
         /// <inheritdoc/>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public override MemoryGroupEnumerator<T> GetEnumerator()
-        {
-            return new MemoryGroupEnumerator<T>(this);
-        }
+        public override MemoryGroupEnumerator<T> GetEnumerator() => new(this);
 
         /// <inheritdoc/>
         IEnumerator<Memory<T>> IEnumerable<Memory<T>>.GetEnumerator()
-        {
+
             /* The runtime sees the Array class as if it implemented the
              * type-generic collection interfaces explicitly, so here we
              * can just cast the source array to IList<Memory<T>> (or to
              * an equivalent type), and invoke the generic GetEnumerator
              * method directly from that interface reference. This saves
              * having to create our own iterator block here. */
-            return ((IList<Memory<T>>)this.source).GetEnumerator();
-        }
+            => ((IList<Memory<T>>)this.source).GetEnumerator();
 
-        public override void Dispose() => this.View.Invalidate();
+        public override void Dispose()
+        {
+            this.View.Invalidate();
+            this.ReleaseAllocationTracking();
+        }
     }
 }

src/ImageSharp/Memory/DiscontiguousBuffers/MemoryGroup{T}.Owned.cs

@@ -73,8 +73,8 @@ internal abstract partial class MemoryGroup<T>
                 result[i] = currentBuffer;
             }
 
-            ObservedBuffer lastBuffer = ObservedBuffer.Create(pooledBuffers[pooledBuffers.Length - 1], sizeOfLastBuffer, options);
-            result[result.Length - 1] = lastBuffer;
+            ObservedBuffer lastBuffer = ObservedBuffer.Create(pooledBuffers[^1], sizeOfLastBuffer, options);
+            result[^1] = lastBuffer;
             return result;
         }
 
@@ -155,6 +155,7 @@ internal abstract partial class MemoryGroup<T>
                 }
             }
 
+            this.ReleaseAllocationTracking();
             this.memoryOwners = null;
             this.IsValid = false;
             this.groupLifetimeGuard = null;

src/ImageSharp/Memory/DiscontiguousBuffers/MemoryGroup{T}.cs

@@ -22,6 +22,9 @@ internal abstract partial class MemoryGroup<T> : IMemoryGroup<T>, IDisposable
     private static readonly int ElementSize = Unsafe.SizeOf<T>();
 
     private MemoryGroupSpanCache memoryGroupSpanCache;
+    private MemoryAllocator? trackingAllocator;
+    private long trackingLengthInBytes;
+    private int trackingReleased;
 
     private MemoryGroup(int bufferLength, long totalLength)
     {
@@ -52,16 +55,45 @@ internal abstract partial class MemoryGroup<T> : IMemoryGroup<T>, IDisposable
     /// <inheritdoc />
     public abstract MemoryGroupEnumerator<T> GetEnumerator();
 
+    /// <summary>
+    /// Configures allocation tracking by specifying the allocator and the length, in bytes, to be tracked.
+    /// </summary>
+    /// <param name="allocator">The memory allocator to use for tracking allocations.</param>
+    /// <param name="lengthInBytes">The length, in bytes, of the memory region to track. Must be greater than or equal to zero.</param>
+    /// <remarks>
+    /// Intended for initialization; callers should avoid changing tracking state concurrently with disposal.
+    /// </remarks>
+    internal void SetAllocationTracking(MemoryAllocator allocator, long lengthInBytes)
+    {
+        this.trackingAllocator = allocator;
+        this.trackingLengthInBytes = lengthInBytes;
+    }
+
+    /// <summary>
+    /// Releases any resources or tracking information associated with allocation tracking for this instance.
+    /// </summary>
+    /// <remarks>
+    /// This method is intended to be called when allocation tracking is no longer needed. It is safe
+    /// to call multiple times; subsequent calls after the first have no effect, even when called concurrently.
+    /// </remarks>
+    internal void ReleaseAllocationTracking()
+    {
+        if (Interlocked.Exchange(ref this.trackingReleased, 1) == 0 && this.trackingAllocator != null)
+        {
+            this.trackingAllocator.ReleaseAccumulatedBytes(this.trackingLengthInBytes);
+            this.trackingAllocator = null;
+        }
+    }
+
     /// <inheritdoc />
     IEnumerator<Memory<T>> IEnumerable<Memory<T>>.GetEnumerator()
-    {
+
         /* This method is implemented in each derived class.
          * Implementing the method here as non-abstract and throwing,
          * then reimplementing it explicitly in each derived class, is
          * a workaround for the lack of support for abstract explicit
          * interface method implementations in C#. */
-        throw new NotImplementedException($"The type {this.GetType()} needs to override IEnumerable<Memory<T>>.GetEnumerator()");
-    }
+        => throw new NotImplementedException($"The type {this.GetType()} needs to override IEnumerable<Memory<T>>.GetEnumerator()");
 
     /// <inheritdoc />
     IEnumerator IEnumerable.GetEnumerator() => ((IEnumerable<Memory<T>>)this).GetEnumerator();

tests/ImageSharp.Tests/Memory/Allocators/SimpleGcMemoryAllocatorTests.cs

@@ -48,6 +48,50 @@ public class SimpleGcMemoryAllocatorTests
         }
     }
 
+    [Fact]
+    public void Allocate_AccumulativeLimit_ReleasesOnOwnerDispose()
+    {
+        SimpleGcMemoryAllocator allocator = new(new MemoryAllocatorOptions
+        {
+            AccumulativeAllocationLimitMegabytes = 1
+        });
+        const int oneMb = 1 << 20;
+
+        // Reserve the full limit with a single owner.
+        IMemoryOwner<byte> b0 = allocator.Allocate<byte>(oneMb);
+
+        // Additional allocation should exceed the limit while the owner is live.
+        Assert.Throws<InvalidMemoryOperationException>(() => allocator.Allocate<byte>(1));
+
+        // Disposing the owner releases the reservation.
+        b0.Dispose();
+
+        // Allocation should succeed after the reservation is released.
+        allocator.Allocate<byte>(oneMb).Dispose();
+    }
+
+    [Fact]
+    public void AllocateGroup_AccumulativeLimit_ReleasesOnGroupDispose()
+    {
+        SimpleGcMemoryAllocator allocator = new(new MemoryAllocatorOptions
+        {
+            AccumulativeAllocationLimitMegabytes = 1
+        });
+        const int oneMb = 1 << 20;
+
+        // Reserve the full limit with a single group.
+        MemoryGroup<byte> g0 = allocator.AllocateGroup<byte>(oneMb, 1024);
+
+        // Additional allocation should exceed the limit while the group is live.
+        Assert.Throws<InvalidMemoryOperationException>(() => allocator.AllocateGroup<byte>(1, 1024));
+
+        // Disposing the group releases the reservation.
+        g0.Dispose();
+
+        // Allocation should succeed after the reservation is released.
+        allocator.AllocateGroup<byte>(oneMb, 1024).Dispose();
+    }
+
     [StructLayout(LayoutKind.Explicit, Size = 512)]
     private struct BigStruct
     {

tests/ImageSharp.Tests/Memory/Allocators/UniformUnmanagedPoolMemoryAllocatorTests.cs

@@ -16,8 +16,8 @@ public class UniformUnmanagedPoolMemoryAllocatorTests
 {
     public class BufferTests1 : BufferTestSuite
     {
-        private static MemoryAllocator CreateMemoryAllocator() =>
-            new UniformUnmanagedMemoryPoolMemoryAllocator(
+        private static UniformUnmanagedMemoryPoolMemoryAllocator CreateMemoryAllocator() =>
+            new(
                 sharedArrayPoolThresholdInBytes: 1024,
                 poolBufferSizeInBytes: 2048,
                 maxPoolSizeInBytes: 2048 * 4,
@@ -31,8 +31,8 @@ public class UniformUnmanagedPoolMemoryAllocatorTests
 
     public class BufferTests2 : BufferTestSuite
     {
-        private static MemoryAllocator CreateMemoryAllocator() =>
-            new UniformUnmanagedMemoryPoolMemoryAllocator(
+        private static UniformUnmanagedMemoryPoolMemoryAllocator CreateMemoryAllocator() =>
+            new(
                 sharedArrayPoolThresholdInBytes: 512,
                 poolBufferSizeInBytes: 1024,
                 maxPoolSizeInBytes: 1024 * 4,
@@ -179,8 +179,8 @@ public class UniformUnmanagedPoolMemoryAllocatorTests
             g1.Dispose();
 
             // Do some unmanaged allocations to make sure new non-pooled unmanaged allocations will grab different memory:
-            IntPtr dummy1 = Marshal.AllocHGlobal((IntPtr)B(8));
-            IntPtr dummy2 = Marshal.AllocHGlobal((IntPtr)B(8));
+            IntPtr dummy1 = Marshal.AllocHGlobal(checked((IntPtr)B(8)));
+            IntPtr dummy2 = Marshal.AllocHGlobal(checked((IntPtr)B(8)));
 
             using MemoryGroup<byte> g2 = allocator.AllocateGroup<byte>(B(8), 1024);
             using MemoryGroup<byte> g3 = allocator.AllocateGroup<byte>(B(8), 1024);
@@ -446,6 +446,50 @@ public class UniformUnmanagedPoolMemoryAllocatorTests
         Assert.Throws<InvalidMemoryOperationException>(() => allocator.AllocateGroup<byte>(5 * oneMb, 1024));
     }
 
+    [Fact]
+    public void Allocate_AccumulativeLimit_ReleasesOnOwnerDispose()
+    {
+        MemoryAllocator allocator = MemoryAllocator.Create(new MemoryAllocatorOptions
+        {
+            AccumulativeAllocationLimitMegabytes = 1
+        });
+        const int oneMb = 1 << 20;
+
+        // Reserve the full limit with a single owner.
+        IMemoryOwner<byte> b0 = allocator.Allocate<byte>(oneMb);
+
+        // Additional allocation should exceed the limit while the owner is live.
+        Assert.Throws<InvalidMemoryOperationException>(() => allocator.Allocate<byte>(1));
+
+        // Disposing the owner releases the reservation.
+        b0.Dispose();
+
+        // Allocation should succeed after the reservation is released.
+        allocator.Allocate<byte>(oneMb).Dispose();
+    }
+
+    [Fact]
+    public void AllocateGroup_AccumulativeLimit_ReleasesOnGroupDispose()
+    {
+        MemoryAllocator allocator = MemoryAllocator.Create(new MemoryAllocatorOptions
+        {
+            AccumulativeAllocationLimitMegabytes = 1
+        });
+        const int oneMb = 1 << 20;
+
+        // Reserve the full limit with a single group.
+        MemoryGroup<byte> g0 = allocator.AllocateGroup<byte>(oneMb, 1024);
+
+        // Additional allocation should exceed the limit while the group is live.
+        Assert.Throws<InvalidMemoryOperationException>(() => allocator.AllocateGroup<byte>(1, 1024));
+
+        // Disposing the group releases the reservation.
+        g0.Dispose();
+
+        // Allocation should succeed after the reservation is released.
+        allocator.AllocateGroup<byte>(oneMb, 1024).Dispose();
+    }
+
     [ConditionalFact(typeof(Environment), nameof(Environment.Is64BitProcess))]
     public void MemoryAllocator_Create_SetHighLimit()
     {

tests/ImageSharp.Tests/Memory/DiscontiguousBuffers/MemoryGroupTests.Allocate.cs

@@ -98,7 +98,15 @@ public partial class MemoryGroupTests
         [InlineData(AllocationOptions.Clean)]
         public unsafe void Allocate_FromPool_AllocationOptionsAreApplied(AllocationOptions options)
         {
-            UniformUnmanagedMemoryPool pool = new(10, 5);
+            // Disable trimming to avoid buffers being freed between Return and TryAllocate by the
+            // trim timer or the Gen2 GC callback.
+            UniformUnmanagedMemoryPool pool = new(
+                10,
+                5,
+                new UniformUnmanagedMemoryPool.TrimSettings
+                {
+                    Rate = 0
+                });
             UnmanagedMemoryHandle[] buffers = pool.Rent(5);
             foreach (UnmanagedMemoryHandle b in buffers)
             {