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- // Licensed to the .NET Foundation under one or more agreements.
- // The .NET Foundation licenses this file to you under the MIT license.
- // See the LICENSE file in the project root for more information.
- #if NETCORE
- using System.Runtime.CompilerServices;
- using System.Threading;
- namespace SharpCompress.Buffers
- {
- /// <summary>
- /// Provides a resource pool that enables reusing instances of type <see cref="T:T[]"/>.
- /// </summary>
- /// <remarks>
- /// <para>
- /// Renting and returning buffers with an <see cref="ArrayPool{T}"/> can increase performance
- /// in situations where arrays are created and destroyed frequently, resulting in significant
- /// memory pressure on the garbage collector.
- /// </para>
- /// <para>
- /// This class is thread-safe. All members may be used by multiple threads concurrently.
- /// </para>
- /// </remarks>
- internal abstract class ArrayPool<T>
- {
- /// <summary>The lazily-initialized shared pool instance.</summary>
- private static ArrayPool<T> s_sharedInstance = null;
- /// <summary>
- /// Retrieves a shared <see cref="ArrayPool{T}"/> instance.
- /// </summary>
- /// <remarks>
- /// The shared pool provides a default implementation of <see cref="ArrayPool{T}"/>
- /// that's intended for general applicability. It maintains arrays of multiple sizes, and
- /// may hand back a larger array than was actually requested, but will never hand back a smaller
- /// array than was requested. Renting a buffer from it with <see cref="Rent"/> will result in an
- /// existing buffer being taken from the pool if an appropriate buffer is available or in a new
- /// buffer being allocated if one is not available.
- /// </remarks>
- public static ArrayPool<T> Shared
- {
- [MethodImpl(MethodImplOptions.AggressiveInlining)]
- get { return Volatile.Read(ref s_sharedInstance) ?? EnsureSharedCreated(); }
- }
- /// <summary>Ensures that <see cref="s_sharedInstance"/> has been initialized to a pool and returns it.</summary>
- [MethodImpl(MethodImplOptions.NoInlining)]
- private static ArrayPool<T> EnsureSharedCreated()
- {
- Interlocked.CompareExchange(ref s_sharedInstance, Create(), null);
- return s_sharedInstance;
- }
- /// <summary>
- /// Creates a new <see cref="ArrayPool{T}"/> instance using default configuration options.
- /// </summary>
- /// <returns>A new <see cref="ArrayPool{T}"/> instance.</returns>
- public static ArrayPool<T> Create()
- {
- return new DefaultArrayPool<T>();
- }
- /// <summary>
- /// Creates a new <see cref="ArrayPool{T}"/> instance using custom configuration options.
- /// </summary>
- /// <param name="maxArrayLength">The maximum length of array instances that may be stored in the pool.</param>
- /// <param name="maxArraysPerBucket">
- /// The maximum number of array instances that may be stored in each bucket in the pool. The pool
- /// groups arrays of similar lengths into buckets for faster access.
- /// </param>
- /// <returns>A new <see cref="ArrayPool{T}"/> instance with the specified configuration options.</returns>
- /// <remarks>
- /// The created pool will group arrays into buckets, with no more than <paramref name="maxArraysPerBucket"/>
- /// in each bucket and with those arrays not exceeding <paramref name="maxArrayLength"/> in length.
- /// </remarks>
- public static ArrayPool<T> Create(int maxArrayLength, int maxArraysPerBucket)
- {
- return new DefaultArrayPool<T>(maxArrayLength, maxArraysPerBucket);
- }
- /// <summary>
- /// Retrieves a buffer that is at least the requested length.
- /// </summary>
- /// <param name="minimumLength">The minimum length of the array needed.</param>
- /// <returns>
- /// An <see cref="T:T[]"/> that is at least <paramref name="minimumLength"/> in length.
- /// </returns>
- /// <remarks>
- /// This buffer is loaned to the caller and should be returned to the same pool via
- /// <see cref="Return"/> so that it may be reused in subsequent usage of <see cref="Rent"/>.
- /// It is not a fatal error to not return a rented buffer, but failure to do so may lead to
- /// decreased application performance, as the pool may need to create a new buffer to replace
- /// the one lost.
- /// </remarks>
- public abstract T[] Rent(int minimumLength);
- /// <summary>
- /// Returns to the pool an array that was previously obtained via <see cref="Rent"/> on the same
- /// <see cref="ArrayPool{T}"/> instance.
- /// </summary>
- /// <param name="array">
- /// The buffer previously obtained from <see cref="Rent"/> to return to the pool.
- /// </param>
- /// <param name="clearArray">
- /// If <c>true</c> and if the pool will store the buffer to enable subsequent reuse, <see cref="Return"/>
- /// will clear <paramref name="array"/> of its contents so that a subsequent consumer via <see cref="Rent"/>
- /// will not see the previous consumer's content. If <c>false</c> or if the pool will release the buffer,
- /// the array's contents are left unchanged.
- /// </param>
- /// <remarks>
- /// Once a buffer has been returned to the pool, the caller gives up all ownership of the buffer
- /// and must not use it. The reference returned from a given call to <see cref="Rent"/> must only be
- /// returned via <see cref="Return"/> once. The default <see cref="ArrayPool{T}"/>
- /// may hold onto the returned buffer in order to rent it again, or it may release the returned buffer
- /// if it's determined that the pool already has enough buffers stored.
- /// </remarks>
- public abstract void Return(T[] array, bool clearArray = false);
- }
- }
- #endif
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