112 lines
4.4 KiB
C#
112 lines
4.4 KiB
C#
// <copyright file="TryGetCreate.cs" company="Moonfire Games">
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// Copyright (c) Moonfire Games.
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// This code is licensed under the MIT license.
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// See LICENSE.md in the source or https://opensource.org/licenses/MIT
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// </copyright>
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namespace MfGames.Locking
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{
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using System;
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using System.Threading;
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/// <summary>
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/// Implements the basic pattern for getting an item from a cache using
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/// the ReaderWriterLockSlim class. This attempts to get it using a read-only
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/// lock. If that fails, it gets an upgradable lock, tries again, and if it
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/// still can't find it, upgrades the lock to a write lock to create it.
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/// </summary>
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public static class TryGetCreate
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{
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/// <summary>
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/// Invokes the try/get/create pattern used a condition to test for it
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/// and a constructor function.
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/// </summary>
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/// <param name="readerWriterLockSlim">The reader writer lock slim.</param>
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/// <param name="conditionHandler">The condition handler.</param>
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/// <param name="createHandler">The create handler.</param>
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public static void Invoke(
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ReaderWriterLockSlim readerWriterLockSlim,
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Func<bool> conditionHandler,
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Action createHandler)
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{
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using (new ReadLock(readerWriterLockSlim))
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{
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// Verify that the condition for creating it is false.
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if (!conditionHandler())
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{
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return;
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}
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}
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// We failed to get the lock using the read-only. We create an upgradable lock
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// and try again since it may have been created with a race condition when the
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// last lock was released and this one was acquired.
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using (new UpgradableLock(readerWriterLockSlim))
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{
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// Verify that the condition for creating it is false.
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if (!conditionHandler())
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{
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return;
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}
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// We failed to get it in the lock. Upgrade the lock to a write and create it.
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using (new WriteLock(readerWriterLockSlim))
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{
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createHandler();
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}
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}
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}
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/// <summary>
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/// Invokes the try/get/create pattern using a tryget retrieval and a
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/// creator handler.
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/// </summary>
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/// <typeparam name="TInput">The type of the input.</typeparam>
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/// <typeparam name="TOutput">The type of the output.</typeparam>
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/// <param name="readerWriterLockSlim">The reader writer lock slim.</param>
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/// <param name="input">The input.</param>
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/// <param name="tryGetHandler">The try get handler.</param>
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/// <param name="createHandler">The create handler.</param>
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/// <returns>The requested output object.</returns>
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public static TOutput Invoke<TInput, TOutput>(
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ReaderWriterLockSlim readerWriterLockSlim,
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TInput input,
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TryGetHandler<TInput, TOutput> tryGetHandler,
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Func<TInput, TOutput> createHandler)
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{
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// First attempt to get the item using a read-only lock.
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TOutput output;
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using (new ReadLock(readerWriterLockSlim))
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{
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// Try to get the item using the try/get handler.
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if (tryGetHandler(input, out output))
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{
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// We successful got the item in the read-only cache, so just return it.
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return output;
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}
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}
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// We failed to get the lock using the read-only. We create an upgradable lock
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// and try again since it may have been created with a race condition when the
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// last lock was released and this one was acquired.
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using (new UpgradableLock(readerWriterLockSlim))
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{
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// Try to get the item using the try/get handler.
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if (tryGetHandler(input, out output))
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{
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// We successful got the item in this lock, so return it without
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// upgrading the lock.
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return output;
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}
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// We failed to get it in the lock. Upgrade the lock to a write and create it.
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using (new WriteLock(readerWriterLockSlim))
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{
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return createHandler(input);
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}
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}
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}
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}
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}
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