SharedPools.cs

// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.

using System;
using System.Collections.Generic;
using Microsoft.CodeAnalysis.PooledObjects;

namespace Microsoft.CodeAnalysis
{
    /// <summary>
    /// Shared object pool for roslyn
    /// 
    /// Use this shared pool if only concern is reducing object allocations.
    /// if perf of an object pool itself is also a concern, use ObjectPool directly.
    /// 
    /// For example, if you want to create a million of small objects within a second, 
    /// use the ObjectPool directly. it should have much less overhead than using this.
    /// </summary>
    internal static class SharedPools
    {
        /// <summary>
        /// pool that uses default constructor with 100 elements pooled
        /// </summary>
        public static ObjectPool<T> BigDefault<T>() where T : class, new()
        {
            return DefaultBigPool<T>.Instance;
        }

        /// <summary>
        /// pool that uses default constructor with 20 elements pooled
        /// </summary>
        public static ObjectPool<T> Default<T>() where T : class, new()
        {
            return DefaultNormalPool<T>.Instance;
        }

        /// <summary>
        /// pool that uses string as key with StringComparer.OrdinalIgnoreCase as key comparer
        /// </summary>
        public static ObjectPool<Dictionary<string, T>> StringIgnoreCaseDictionary<T>()
        {
            return StringIgnoreCaseDictionaryNormalPool<T>.Instance;
        }

        /// <summary>
        /// pool that uses string as element with StringComparer.OrdinalIgnoreCase as element comparer
        /// </summary>
        public static readonly ObjectPool<HashSet<string>> StringIgnoreCaseHashSet =
            new ObjectPool<HashSet<string>>(() => new HashSet<string>(StringComparer.OrdinalIgnoreCase), 20);

        /// <summary>
        /// pool that uses string as element with StringComparer.Ordinal as element comparer
        /// </summary>
        public static readonly ObjectPool<HashSet<string>> StringHashSet =
            new ObjectPool<HashSet<string>>(() => new HashSet<string>(StringComparer.Ordinal), 20);

        /// <summary>
        /// Used to reduce the # of temporary byte[]s created to satisfy serialization and
        /// other I/O requests
        /// </summary>
        public static readonly ObjectPool<byte[]> ByteArray = new ObjectPool<byte[]>(() => new byte[ByteBufferSize], ByteBufferCount);
        public static readonly ObjectPool<char[]> CharArray = new ObjectPool<char[]>(() => new char[ByteBufferSize], CharBufferCount);

        // byte pooled memory : 4K * 512 = 4MB
        public const int ByteBufferSize = 4 * 1024;
        private const int ByteBufferCount = 512;

        // char pooled memory : 8K * 5 = 40K
        private const int CharBufferCount = 5;

        private static class DefaultBigPool<T> where T : class, new()
        {
            public static readonly ObjectPool<T> Instance = new ObjectPool<T>(() => new T(), 100);
        }

        private static class DefaultNormalPool<T> where T : class, new()
        {
            public static readonly ObjectPool<T> Instance = new ObjectPool<T>(() => new T(), 20);
        }

        private static class StringIgnoreCaseDictionaryNormalPool<T>
        {
            public static readonly ObjectPool<Dictionary<string, T>> Instance =
                new ObjectPool<Dictionary<string, T>>(() => new Dictionary<string, T>(StringComparer.OrdinalIgnoreCase), 20);
        }
    }
}