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using System;
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using Implab.Parallels;
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using System.Threading;
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using System.Diagnostics;
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using System.Diagnostics.CodeAnalysis;
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namespace Implab.Components {
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/// <summary>
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/// The base class for implementing thread-safe pools of disposable objects.
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/// </summary>
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/// <remarks>
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/// <para>This class maintains a set of pre-created objects which are frequently allocated and released
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/// by clients. The pool maintains maximum number of unsued object, any object above this limit is disposed,
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/// if the pool is empty it will create new objects on demand.</para>
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/// <para>Instances of this class are thread-safe.</para>
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/// </remarks>
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public abstract class DisposablePool<T> : IDisposable {
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readonly int m_size;
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readonly AsyncQueue<T> m_queue = new AsyncQueue<T>();
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[SuppressMessage("Microsoft.Design", "CA1000:DoNotDeclareStaticMembersOnGenericTypes")]
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static readonly bool _isValueType = typeof(T).IsValueType;
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bool m_disposed;
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int m_count;
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protected DisposablePool(int size) {
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m_size = size;
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}
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protected DisposablePool() : this(Environment.ProcessorCount+1) {
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}
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public T Allocate() {
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if (m_disposed)
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throw new ObjectDisposedException(ToString());
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T instance;
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if (m_queue.TryDequeue(out instance)) {
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Interlocked.Decrement(ref m_count);
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} else {
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instance = CreateInstance();
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Debug.Assert(!Object.Equals(instance, default(T)) || _isValueType);
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}
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return instance;
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}
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protected abstract T CreateInstance();
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protected virtual void CleanupInstance(T instance) {
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}
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public void Release(T instance) {
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if ( Object.Equals(instance,default(T)) && !_isValueType)
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return;
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Thread.MemoryBarrier();
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if (m_count < m_size && !m_disposed) {
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Interlocked.Increment(ref m_count);
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CleanupInstance(instance);
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m_queue.Enqueue(instance);
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// пока элемент возвращался в кеш, была начата операция освобождения всего кеша
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// и возможно уже законцена, в таком случае следует извлечь элемент обратно и
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// освободить его. Если операция освобождения кеша еще не заврешилась, то будет
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// изъят и освобожден произвольный элемен, что не повлияет на ход всего процесса.
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if (m_disposed && m_queue.TryDequeue(out instance) && instance is IDisposable)
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((IDisposable)instance).Dispose() ;
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} else {
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var disposable = instance as IDisposable;
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if (disposable != null)
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disposable.Dispose();
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}
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}
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protected virtual void Dispose(bool disposing) {
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if (disposing) {
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m_disposed = true;
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T instance;
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while (m_queue.TryDequeue(out instance)) {
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var disposable = instance as IDisposable;
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if (disposable != null)
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disposable.Dispose();
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}
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}
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}
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#region IDisposable implementation
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public void Dispose() {
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Dispose(true);
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GC.SuppressFinalize(this);
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}
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#endregion
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}
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}
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