86 lines
3.0 KiB
C#
86 lines
3.0 KiB
C#
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// ==++==
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//
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// Copyright (c) Microsoft Corporation. All rights reserved.
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//
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// ==--==
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/*============================================================
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**
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** Class: StringBuilderCache
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**
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** Purpose: provide a cached reusable instance of stringbuilder
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** per thread it's an optimisation that reduces the
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** number of instances constructed and collected.
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**
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** Acquire - is used to get a string builder to use of a
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** particular size. It can be called any number of
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** times, if a stringbuilder is in the cache then
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** it will be returned and the cache emptied.
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** subsequent calls will return a new stringbuilder.
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**
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** A StringBuilder instance is cached in
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** Thread Local Storage and so there is one per thread
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**
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** Release - Place the specified builder in the cache if it is
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** not too big.
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** The stringbuilder should not be used after it has
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** been released.
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** Unbalanced Releases are perfectly acceptable. It
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** will merely cause the runtime to create a new
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** stringbuilder next time Acquire is called.
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**
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** GetStringAndRelease
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** - ToString() the stringbuilder, Release it to the
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** cache and return the resulting string
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**
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===========================================================*/
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using System.Threading;
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namespace System.Text
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{
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internal static class StringBuilderCache
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{
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// The value 360 was chosen in discussion with performance experts as a compromise between using
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// as litle memory (per thread) as possible and still covering a large part of short-lived
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// StringBuilder creations on the startup path of VS designers.
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private const int MAX_BUILDER_SIZE = 360;
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[ThreadStatic]
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private static StringBuilder CachedInstance;
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public static StringBuilder Acquire(int capacity = StringBuilder.DefaultCapacity)
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{
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if(capacity <= MAX_BUILDER_SIZE)
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{
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StringBuilder sb = StringBuilderCache.CachedInstance;
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if (sb != null)
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{
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// Avoid stringbuilder block fragmentation by getting a new StringBuilder
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// when the requested size is larger than the current capacity
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if(capacity <= sb.Capacity)
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{
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StringBuilderCache.CachedInstance = null;
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sb.Clear();
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return sb;
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}
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}
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}
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return new StringBuilder(capacity);
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}
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public static void Release(StringBuilder sb)
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{
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if (sb.Capacity <= MAX_BUILDER_SIZE)
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{
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StringBuilderCache.CachedInstance = sb;
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}
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}
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public static string GetStringAndRelease(StringBuilder sb)
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{
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string result = sb.ToString();
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Release(sb);
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return result;
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}
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}
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}
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