Check if image is disposed

in significant Image and Image<T> methods

src/ImageSharp/Image.cs

@@ -80,8 +80,22 @@ internal Image(
         /// </summary>
         Configuration IConfigurable.Configuration => this.Configuration;
 
+        /// <summary>
+        /// Gets a value indicating whether the image instance is disposed.
+        /// </summary>
+        public bool IsDisposed { get; private set; }
+
         /// <inheritdoc />
-        public abstract void Dispose();
+        public void Dispose()
+        {
+            if (this.IsDisposed)
+            {
+                return;
+            }
+
+            this.IsDisposed = true;
+            this.DisposeImpl();
+        }
 
         /// <summary>
         /// Saves the image to the given stream using the given image encoder.
@@ -128,6 +142,11 @@ public abstract Image<TPixel2> CloneAs<TPixel2>(Configuration configuration)
         /// <param name="size">The <see cref="Size"/>.</param>
         protected void UpdateSize(Size size) => this.size = size;
 
+        /// <summary>
+        /// Implements the Dispose logic.
+        /// </summary>
+        protected abstract void DisposeImpl();
+
         private class EncodeVisitor : IImageVisitor
         {
             private readonly IImageEncoder encoder;

src/ImageSharp/ImageExtensions.cs

@@ -119,5 +119,16 @@ public static string ToBase64String<TPixel>(this Image<TPixel> source, IImageFor
                 return $"data:{format.DefaultMimeType};base64,{Convert.ToBase64String(stream.ToArray())}";
             }
         }
+
+        /// <summary>
+        /// Throws <see cref="ObjectDisposedException"/> if the image is disposed.
+        /// </summary>
+        internal static void CheckDisposed(this Image image)
+        {
+            if (image.IsDisposed)
+            {
+                throw new ObjectDisposedException(nameof(image), "Trying to execute an operation on a disposed image.");
+            }
+        }
     }
-}
+}

src/ImageSharp/Image{TPixel}.cs

@@ -162,6 +162,8 @@ internal Image(Configuration configuration, ImageMetadata metadata, IEnumerable<
         /// <returns>Returns a new <see cref="Image{TPixel}"/> with all the same pixel data as the original.</returns>
         public Image<TPixel> Clone(Configuration configuration)
         {
+            this.CheckDisposed();
+
             IEnumerable<ImageFrame<TPixel>> clonedFrames =
                 this.Frames.Select<ImageFrame<TPixel>, ImageFrame<TPixel>>(x => x.Clone(configuration));
             return new Image<TPixel>(configuration, this.Metadata.DeepClone(), clonedFrames);
@@ -175,17 +177,21 @@ public Image<TPixel> Clone(Configuration configuration)
         /// <returns>The <see cref="Image{TPixel2}"/>.</returns>
         public override Image<TPixel2> CloneAs<TPixel2>(Configuration configuration)
         {
+            this.CheckDisposed();
+
             IEnumerable<ImageFrame<TPixel2>> clonedFrames =
                 this.Frames.Select<ImageFrame<TPixel>, ImageFrame<TPixel2>>(x => x.CloneAs<TPixel2>(configuration));
             return new Image<TPixel2>(configuration, this.Metadata.DeepClone(), clonedFrames);
         }
 
         /// <inheritdoc/>
-        public override void Dispose() => this.Frames.Dispose();
+        protected override void DisposeImpl() => this.Frames.Dispose();
 
         /// <inheritdoc />
         internal override void AcceptVisitor(IImageVisitor visitor)
         {
+            this.CheckDisposed();
+
             visitor.Visit(this);
         }
 

tests/ImageSharp.Tests/Image/ImageCloneTests.cs

@@ -7,6 +7,24 @@ namespace SixLabors.ImageSharp.Tests
 {
     public class ImageCloneTests
     {
+        [Fact]
+        public void CloneAs_WhenDisposed_Throws()
+        {
+            Image<Rgba32> image = new Image<Rgba32>(5, 5);
+            image.Dispose();
+
+            Assert.Throws<ObjectDisposedException>(() => image.CloneAs<Bgra32>());
+        }
+
+        [Fact]
+        public void Clone_WhenDisposed_Throws()
+        {
+            Image<Rgba32> image = new Image<Rgba32>(5, 5);
+            image.Dispose();
+
+            Assert.Throws<ObjectDisposedException>(() => image.Clone());
+        }
+
         [Theory]
         [WithTestPatternImages(9, 9, PixelTypes.Rgba32)]
         public void CloneAs_ToBgra32(TestImageProvider<Rgba32> provider)
@@ -109,4 +127,4 @@ public void CloneAs_ToRgb24(TestImageProvider<Rgba32> provider)
             }
         }
     }
-}
+}

tests/ImageSharp.Tests/Image/ImageTests.Save.cs

@@ -4,6 +4,10 @@
 // ReSharper disable InconsistentNaming
 
 using System;
+using System.IO;
+
+using Moq;
+
 using SixLabors.ImageSharp.Formats.Png;
 using SixLabors.ImageSharp.PixelFormats;
 using Xunit;
@@ -65,6 +69,18 @@ public void SetEncoding()
                     Assert.Equal("image/png", mime.DefaultMimeType);
                 }
             }
+
+            [Fact]
+            public void ThrowsWhenDisposed()
+            {
+                var image = new Image<Rgba32>(5, 5);
+                image.Dispose();
+                IImageEncoder encoder = Mock.Of<IImageEncoder>();
+                using (MemoryStream stream = new MemoryStream())
+                {
+                    Assert.Throws<ObjectDisposedException>(() => image.Save(stream, encoder));
+                }
+            }
         }
     }
 }