Design and performance improvement: introduces internal object pooling, refactors rendering and dialog infrastructure, and tightens API visibility

App.axaml.cs

@@ -48,6 +48,7 @@ namespace MermaidPad;
 /// running.</remarks>
 public sealed partial class App : Application, IDisposable
 {
+    private const int StringBuilderInitialCapacity = 512;
     public static IServiceProvider Services { get; private set; } = null!;
     private static readonly string[] _newlineCharacters = ["\r\n", "\r", "\n"];
 
@@ -377,7 +378,7 @@ private async Task ShowErrorDialogCoreAsync(Exception exception, string userMess
             string fullExceptionDetails = BuildExceptionDetails(exception);
 
             // Build user-facing summary
-            StringBuilder errorSummary = new StringBuilder();
+            StringBuilder errorSummary = new StringBuilder(StringBuilderInitialCapacity);
             errorSummary.AppendLine(userMessage);
             errorSummary.AppendLine();
             errorSummary.AppendLine($"Error Type: {exception.GetType().FullName}");
@@ -786,7 +787,7 @@ static async Task SafeSetButtonContentAsync(Button btn, object? content)
     /// <param name="threadContext">A string representing the logical context or name of the thread where the exception occurred - e.g. "UI Thread", "Background Thread", "ThreadPool Thread".</param>
     private static void LogFatalExceptionWithContext(string message, Exception exception, string threadContext)
     {
-        StringBuilder logEntry = new StringBuilder(256);
+        StringBuilder logEntry = new StringBuilder(StringBuilderInitialCapacity);
         logEntry.AppendLine("---------------------------------------------------------------");
         logEntry.AppendLine($"EXCEPTION: {message}");
         logEntry.AppendLine($"Time: {DateTime.Now:yyyy-MM-dd HH:mm:ss.fff}");
@@ -822,7 +823,7 @@ private static void LogFatalExceptionWithContext(string message, Exception excep
     /// and stack trace where applicable.</returns>
     private static string BuildExceptionDetails(Exception exception)
     {
-        StringBuilder details = new StringBuilder();
+        StringBuilder details = new StringBuilder(StringBuilderInitialCapacity);
 
         // Handle AggregateException specially to show all inner exceptions
         if (exception is AggregateException aggregateException)
@@ -884,7 +885,7 @@ private static string BuildExceptionDetails(Exception exception)
     /// location, source assembly, target site, custom data, and optionally the stack trace.</returns>
     private static string FormatSingleException(Exception exception, bool includeStackTrace)
     {
-        StringBuilder details = new StringBuilder();
+        StringBuilder details = new StringBuilder(StringBuilderInitialCapacity);
 
         details.AppendLine($"Exception Type: {exception.GetType().FullName}");
         details.AppendLine($"Message: {exception.Message}");

Infrastructure/DialogFactory.cs

@@ -27,7 +27,7 @@ namespace MermaidPad.Infrastructure;
 /// <summary>
 /// Factory for creating dialogs with proper dependency injection
 /// </summary>
-public interface IDialogFactory
+internal interface IDialogFactory
 {
     /// <summary>
     /// Creates a dialog window with DI support
@@ -43,7 +43,7 @@ public interface IDialogFactory
 /// <summary>
 /// Implementation of dialog factory using the service provider
 /// </summary>
-public sealed class DialogFactory : IDialogFactory
+internal sealed class DialogFactory : IDialogFactory
 {
     private readonly IServiceProvider _serviceProvider;
 

Infrastructure/ObjectPooling/IPooledStringBuilderLeaseFactory.cs

@@ -0,0 +1,72 @@
+// MIT License
+// Copyright (c) 2025 Dave Black
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+using JetBrains.Annotations;
+using System.Text;
+
+namespace MermaidPad.Infrastructure.ObjectPooling;
+
+/// <summary>
+/// Defines a factory for obtaining pooled leases of <see cref="StringBuilder"/> instances.
+/// </summary>
+/// <remarks>Implementations of this interface provide a mechanism to rent and return <see cref="StringBuilder"/> objects from a
+/// pool, which can help reduce memory allocations in scenarios with frequent string manipulations. The returned lease
+/// typically manages the lifecycle of the pooled <see cref="StringBuilder"/>, ensuring it is returned to the pool when
+/// disposed.</remarks>
+internal interface IPooledStringBuilderLeaseFactory
+{
+    /// <summary>
+    /// Rents a pooled <see cref="StringBuilder"/> instance wrapped in a <see cref="PooledStringBuilderLease"/>.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// The caller:
+    ///     1. Must dispose of the returned <see cref="PooledStringBuilderLease"/> to return the <see cref="StringBuilder"/> to the pool
+    ///     as indicated by the <see cref="MustDisposeResourceAttribute"/>.
+    ///     2. Must avoid holding onto the <see cref="StringBuilder"/> reference beyond the scope of the lease.
+    ///     3. Must use the return value as indicated by the <see cref="MustUseReturnValueAttribute"/>.
+    /// </para>
+    /// </remarks>
+    /// <returns>A <see cref="PooledStringBuilderLease"/> that provides exclusive access to a pooled <see cref="StringBuilder"/>.
+    /// The lease must be disposed to return the <see cref="StringBuilder"/> to the pool.</returns>
+    [MustDisposeResource]
+    [MustUseReturnValue]
+    PooledStringBuilderLease Rent();
+
+    /// <summary>
+    /// Rents a pooled <see cref="StringBuilder"/> instance wrapped in a <see cref="PooledStringBuilderLease"/>.
+    /// </summary>
+    /// <param name="minimumCapacity">The minimum capacity the rented <see cref="StringBuilder"/> should have.</param>
+    /// <remarks>
+    /// <para>
+    /// The caller:
+    ///     1. Must dispose of the returned <see cref="PooledStringBuilderLease"/> to return the <see cref="StringBuilder"/> to the pool
+    ///     as indicated by the <see cref="MustDisposeResourceAttribute"/>.
+    ///     2. Must avoid holding onto the <see cref="StringBuilder"/> reference beyond the scope of the lease.
+    ///     3. Must use the return value as indicated by the <see cref="MustUseReturnValueAttribute"/>.
+    /// </para>
+    /// </remarks>
+    /// <returns>A <see cref="PooledStringBuilderLease"/> that provides exclusive access to a pooled <see cref="StringBuilder"/>.
+    /// The lease must be disposed to return the <see cref="StringBuilder"/> to the pool.</returns>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown when <paramref name="minimumCapacity"/> is less than or equal to zero.</exception>
+    [MustDisposeResource]
+    [MustUseReturnValue]
+    PooledStringBuilderLease Rent(int minimumCapacity);
+}

Infrastructure/ObjectPooling/ObjectPoolRegistrations.cs

@@ -0,0 +1,103 @@
+// MIT License
+// Copyright (c) 2025 Dave Black
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+using MermaidPad.ObjectPoolPolicies;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
+using Microsoft.Extensions.ObjectPool;
+using System.Text;
+
+namespace MermaidPad.Infrastructure.ObjectPooling;
+
+/// <summary>
+/// Provides registration methods for configuring object pooling services, such as StringBuilder pooling, within a
+/// dependency injection container.
+/// </summary>
+/// <remarks>This class is intended for internal use to centralize object pool service registrations. It is not
+/// intended to be used directly by application code.</remarks>
+internal static class ObjectPoolRegistrations
+{
+    /// <summary>
+    /// Adds object pooling services to the specified <see cref="IServiceCollection"/>. Registers default object pool
+    /// providers and policies for use within the application.
+    /// </summary>
+    /// <remarks>This method registers a default <see cref="ObjectPoolProvider"/> and configures object pools
+    /// for commonly used types such as <see cref="HashSet{String}"/> and <see cref="StringBuilder"/>. Call this method
+    /// during service configuration to enable efficient object reuse and reduce memory allocations.</remarks>
+    /// <param name="services">The <see cref="IServiceCollection"/> to which the object pooling services are added. Cannot be null.</param>
+    internal static void AddObjectPooling(this IServiceCollection services)
+    {
+        // Register the default object pool provider first if one is not already registered
+        services.TryAddSingleton<ObjectPoolProvider, DefaultObjectPoolProvider>();
+        services.TryAddSingleton<ObjectPool<HashSet<string>>>(static sp =>
+        {
+            ObjectPoolProvider provider = sp.GetRequiredService<ObjectPoolProvider>();
+            HashSetPooledObjectPolicy policy = new HashSetPooledObjectPolicy();
+            return provider.Create(policy);
+        });
+
+        services.TryAddSingleton<IPooledStringBuilderLeaseFactory>(CreatePooledStringBuilderLeaseFactory);
+    }
+
+    /// <summary>
+    /// Creates an object pool for <see cref="StringBuilder"/> instances using the specified service provider.
+    /// </summary>
+    /// <remarks>The returned <see cref="IPooledStringBuilderLeaseFactory"/> is configured to provide a pool with
+    /// an initial capacity of 256 characters and a maximum retained capacity of 16,384 characters per
+    /// <see cref="StringBuilder"/> instance. Using a pool can improve performance by reducing allocations when working with temporary strings.</remarks>
+    /// <param name="serviceProvider">The service provider used to retrieve the <see cref="ObjectPoolProvider"/> required to create the pool.
+    /// Cannot be null.</param>
+    /// <returns>An <see cref="IPooledStringBuilderLeaseFactory"/> that provides access to pooled <see cref="StringBuilder"/> instances.</returns>
+    private static IPooledStringBuilderLeaseFactory CreatePooledStringBuilderLeaseFactory(IServiceProvider serviceProvider)
+    {
+        const int oneKiloByte = 1_024;
+        ObjectPoolProvider poolProvider = serviceProvider.GetRequiredService<ObjectPoolProvider>();
+        StringBuilderPooledObjectPolicy policy256 = new StringBuilderPooledObjectPolicy
+        {
+            InitialCapacity = 256,
+            MaximumRetainedCapacity = 256
+        };
+
+        StringBuilderPooledObjectPolicy policy1024 = new StringBuilderPooledObjectPolicy
+        {
+            InitialCapacity = oneKiloByte,
+            MaximumRetainedCapacity = oneKiloByte
+        };
+
+        StringBuilderPooledObjectPolicy policy4096 = new StringBuilderPooledObjectPolicy
+        {
+            InitialCapacity = 4 * oneKiloByte,
+            MaximumRetainedCapacity = 4 * oneKiloByte
+        };
+
+        StringBuilderPooledObjectPolicy policy16384 = new StringBuilderPooledObjectPolicy
+        {
+            InitialCapacity = 16 * oneKiloByte,
+            MaximumRetainedCapacity = 16 * oneKiloByte
+        };
+
+        ObjectPool<StringBuilder> pool256 = poolProvider.Create(policy256);
+        ObjectPool<StringBuilder> pool1024 = poolProvider.Create(policy1024);
+        ObjectPool<StringBuilder> pool4096 = poolProvider.Create(policy4096);
+        ObjectPool<StringBuilder> pool16384 = poolProvider.Create(policy16384);
+
+        return new PooledStringBuilderBucketedLeaseFactory(pool256, pool1024, pool4096, pool16384);
+    }
+}