MemoryAllocator.Default

src/ImageSharp/Configuration.cs

@@ -126,7 +126,7 @@ namespace SixLabors.ImageSharp
         /// <summary>
         /// Gets or sets the <see cref="MemoryAllocator"/> that is currently in use.
         /// </summary>
-        public MemoryAllocator MemoryAllocator { get; set; } = MemoryAllocator.Create();
+        public MemoryAllocator MemoryAllocator { get; set; } = MemoryAllocator.Default;
 
         /// <summary>
         /// Gets the maximum header size of all the formats.

src/ImageSharp/Memory/Allocators/MemoryAllocator.cs

@@ -11,6 +11,27 @@ namespace SixLabors.ImageSharp.Memory
     /// </summary>
     public abstract class MemoryAllocator
     {
+        private static MemoryAllocator defaultMemoryAllocator = Create();
+
+        /// <summary>
+        /// Gets or sets the default global <see cref="MemoryAllocator"/> instance for the current process.
+        /// </summary>
+        /// <remarks>
+        /// Since <see cref="Configuration.Default"/> is lazy-initialized, setting the value of <see cref="Default"/>
+        /// will only override <see cref="Configuration.Default"/>'s <see cref="Configuration.MemoryAllocator"/>
+        /// before the first read of the <see cref="Configuration.Default"/> property.
+        /// After that, a manual assigment of <see cref="Configuration.Default"/> is necessary.
+        /// </remarks>
+        public static MemoryAllocator Default
+        {
+            get => defaultMemoryAllocator;
+            set
+            {
+                Guard.NotNull(value, nameof(Default));
+                defaultMemoryAllocator = value;
+            }
+        }
+
         /// <summary>
         /// Gets the length of the largest contiguous buffer that can be handled by this allocator instance in bytes.
         /// </summary>

tests/ImageSharp.Tests/ConfigurationTests.cs

@@ -3,10 +3,12 @@
 
 using System;
 using System.Linq;
+using Microsoft.DotNet.RemoteExecutor;
 using Moq;
 using SixLabors.ImageSharp.Formats.Bmp;
 using SixLabors.ImageSharp.IO;
-
+using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.Tests.Memory;
 using Xunit;
 
 // ReSharper disable InconsistentNaming
@@ -146,5 +148,33 @@ namespace SixLabors.ImageSharp.Tests
             Assert.Throws<ArgumentOutOfRangeException>(
                     () => config.StreamProcessingBufferSize = 0);
         }
+
+        [Fact]
+        public void InheritsDefaultMemoryAllocatorInstance()
+        {
+            RemoteExecutor.Invoke(RunTest).Dispose();
+
+            static void RunTest()
+            {
+                MemoryAllocator allocator = new TestMemoryAllocator();
+                MemoryAllocator.Default = allocator;
+
+                var c1 = new Configuration();
+                var c2 = new Configuration(new MockConfigurationModule());
+                var c3 = Configuration.CreateDefaultInstance();
+
+                Assert.Same(allocator, Configuration.Default.MemoryAllocator);
+                Assert.Same(allocator, c1.MemoryAllocator);
+                Assert.Same(allocator, c2.MemoryAllocator);
+                Assert.Same(allocator, c3.MemoryAllocator);
+            }
+        }
+
+        private class MockConfigurationModule : IConfigurationModule
+        {
+            public void Configure(Configuration configuration)
+            {
+            }
+        }
     }
 }