Parallel 与 ConcurrentBag<T> 这对儿黄金搭档（C#）【并发编程系列_2】

阅读目录

〇、前言
一、ConcurrentBag 简介
二、Parallel 的使用
三、简单总结一下下

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〇、前言

日常开发中经常会遇到数据统计，特别是关于报表的项目。数据处理的效率和准确度当然是首要关注点。

本文主要介绍，如何通过 Parallel 来并行处理数据，并组合 ConcurrentBag<T> 集合，来将处理效率达到高点的同时，也能确保数据的准确。

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一、ConcurrentBag<T> 简介

1、简介与源码

ConcurrentBag<T>，表示对象的线程安全的无序集合。ConcurrentBag 内部将数据按线程的标识独立进行存储，程序可以在同一个线程中插入、删除元素，所以每个线程对其数据的操作是非常快的。

下面是源码供参考：

点击展开 ConcurrentBag 源码

 // System.Collections.Concurrent, Version=5.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
// System.Collections.Concurrent.ConcurrentBag<T>
using System;
using System.Collections;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Threading;
 
[DebuggerTypeProxy(typeof(System.Collections.Concurrent.IProducerConsumerCollectionDebugView<>))]
[DebuggerDisplay("Count = {Count}")]
public class ConcurrentBag<T> : IProducerConsumerCollection<T>, IEnumerable<T>, IEnumerable, ICollection, IReadOnlyCollection<T>
{
	private sealed class WorkStealingQueue
	{
		private volatile int _headIndex;
 
		private volatile int _tailIndex;
 
		private volatile T[] _array = new T[32];
 
		private volatile int _mask = 31;
 
		private int _addTakeCount;
 
		private int _stealCount;
 
		internal volatile int _currentOp;
 
		internal bool _frozen;
 
		internal readonly WorkStealingQueue _nextQueue;
 
		internal readonly int _ownerThreadId;
 
		internal bool IsEmpty => _headIndex - _tailIndex >= 0;
 
		internal int DangerousCount
		{
			get
			{
				int stealCount = _stealCount;
				int addTakeCount = _addTakeCount;
				return addTakeCount - stealCount;
			}
		}
 
		internal WorkStealingQueue(WorkStealingQueue nextQueue)
		{
			_ownerThreadId = Environment.CurrentManagedThreadId;
			_nextQueue = nextQueue;
		}
 
		internal void LocalPush(T item, ref long emptyToNonEmptyListTransitionCount)
		{
			bool lockTaken = false;
			try
			{
				Interlocked.Exchange(ref _currentOp, 1);
				int num = _tailIndex;
				if (num == int.MaxValue)
				{
					_currentOp = 0;
					lock (this)
					{
						_headIndex &= _mask;
						num = (_tailIndex = num & _mask);
						Interlocked.Exchange(ref _currentOp, 1);
					}
				}
				int headIndex = _headIndex;
				if (!_frozen && headIndex - (num - 1) < 0 && num - (headIndex + _mask) < 0)
				{
					_array[num & _mask] = item;
					_tailIndex = num + 1;
				}
				else
				{
					_currentOp = 0;
					Monitor.Enter(this, ref lockTaken);
					headIndex = _headIndex;
					int num2 = num - headIndex;
					if (num2 >= _mask)
					{
						T[] array = new T[_array.Length << 1];
						int num3 = headIndex & _mask;
						if (num3 == 0)
						{
							Array.Copy(_array, array, _array.Length);
						}
						else
						{
							Array.Copy(_array, num3, array, 0, _array.Length - num3);
							Array.Copy(_array, 0, array, _array.Length - num3, num3);
						}
						_array = array;
						_headIndex = 0;
						num = (_tailIndex = num2);
						_mask = (_mask << 1) | 1;
					}
					_array[num & _mask] = item;
					_tailIndex = num + 1;
					if (num2 == 0)
					{
						Interlocked.Increment(ref emptyToNonEmptyListTransitionCount);
					}
					_addTakeCount -= _stealCount;
					_stealCount = 0;
				}
				checked
				{
					_addTakeCount++;
				}
			}
			finally
			{
				_currentOp = 0;
				if (lockTaken)
				{
					Monitor.Exit(this);
				}
			}
		}
 
		internal void LocalClear()
		{
			lock (this)
			{
				if (_headIndex - _tailIndex < 0)
				{
					_headIndex = (_tailIndex = 0);
					_addTakeCount = (_stealCount = 0);
					Array.Clear(_array, 0, _array.Length);
				}
			}
		}
 
		internal bool TryLocalPop([MaybeNullWhen(false)] out T result)
		{
			int tailIndex = _tailIndex;
			if (_headIndex - tailIndex >= 0)
			{
				result = default(T);
				return false;
			}
			bool lockTaken = false;
			try
			{
				_currentOp = 2;
				Interlocked.Exchange(ref _tailIndex, --tailIndex);
				if (!_frozen && _headIndex - tailIndex < 0)
				{
					int num = tailIndex & _mask;
					result = _array[num];
					_array[num] = default(T);
					_addTakeCount--;
					return true;
				}
				_currentOp = 0;
				Monitor.Enter(this, ref lockTaken);
				if (_headIndex - tailIndex <= 0)
				{
					int num2 = tailIndex & _mask;
					result = _array[num2];
					_array[num2] = default(T);
					_addTakeCount--;
					return true;
				}
				_tailIndex = tailIndex + 1;
				result = default(T);
				return false;
			}
			finally
			{
				_currentOp = 0;
				if (lockTaken)
				{
					Monitor.Exit(this);
				}
			}
		}
 
		internal bool TryLocalPeek([MaybeNullWhen(false)] out T result)
		{
			int tailIndex = _tailIndex;
			if (_headIndex - tailIndex < 0)
			{
				lock (this)
				{
					if (_headIndex - tailIndex < 0)
					{
						result = _array[(tailIndex - 1) & _mask];
						return true;
					}
				}
			}
			result = default(T);
			return false;
		}
 
		internal bool TrySteal([MaybeNullWhen(false)] out T result, bool take)
		{
			lock (this)
			{
				int headIndex = _headIndex;
				if (take)
				{
					if (headIndex - (_tailIndex - 2) >= 0 && _currentOp == 1)
					{
						SpinWait spinWait = default(SpinWait);
						do
						{
							spinWait.SpinOnce();
						}
						while (_currentOp == 1);
					}
					Interlocked.Exchange(ref _headIndex, headIndex + 1);
					if (headIndex < _tailIndex)
					{
						int num = headIndex & _mask;
						result = _array[num];
						_array[num] = default(T);
						_stealCount++;
						return true;
					}
					_headIndex = headIndex;
				}
				else if (headIndex < _tailIndex)
				{
					result = _array[headIndex & _mask];
					return true;
				}
			}
			result = default(T);
			return false;
		}
 
		internal int DangerousCopyTo(T[] array, int arrayIndex)
		{
			int headIndex = _headIndex;
			int dangerousCount = DangerousCount;
			for (int num = arrayIndex + dangerousCount - 1; num >= arrayIndex; num--)
			{
				array[num] = _array[headIndex++ & _mask];
			}
			return dangerousCount;
		}
	}
 
	private sealed class Enumerator : IEnumerator<T>, IDisposable, IEnumerator
	{
		private readonly T[] _array;
 
		private T _current;
 
		private int _index;
 
		public T Current => _current;
 
		object IEnumerator.Current
		{
			get
			{
				if (_index == 0 || _index == _array.Length + 1)
				{
					throw new InvalidOperationException(System.SR.ConcurrentBag_Enumerator_EnumerationNotStartedOrAlreadyFinished);
				}
				return Current;
			}
		}
 
		public Enumerator(T[] array)
		{
			_array = array;
		}
 
		public bool MoveNext()
		{
			if (_index < _array.Length)
			{
				_current = _array[_index++];
				return true;
			}
			_index = _array.Length + 1;
			return false;
		}
 
		public void Reset()
		{
			_index = 0;
			_current = default(T);
		}
 
		public void Dispose()
		{
		}
	}
 
	private readonly ThreadLocal<WorkStealingQueue> _locals;
 
	private volatile WorkStealingQueue _workStealingQueues;
 
	private long _emptyToNonEmptyListTransitionCount;
 
	public int Count
	{
		get
		{
			if (_workStealingQueues == null)
			{
				return 0;
			}
			bool lockTaken = false;
			try
			{
				FreezeBag(ref lockTaken);
				return DangerousCount;
			}
			finally
			{
				UnfreezeBag(lockTaken);
			}
		}
	}
 
	private int DangerousCount
	{
		get
		{
			int num = 0;
			for (WorkStealingQueue workStealingQueue = _workStealingQueues; workStealingQueue != null; workStealingQueue = workStealingQueue._nextQueue)
			{
				num = checked(num + workStealingQueue.DangerousCount);
			}
			return num;
		}
	}
 
	public bool IsEmpty
	{
		get
		{
			WorkStealingQueue currentThreadWorkStealingQueue = GetCurrentThreadWorkStealingQueue(forceCreate: false);
			if (currentThreadWorkStealingQueue != null)
			{
				if (!currentThreadWorkStealingQueue.IsEmpty)
				{
					return false;
				}
				if (currentThreadWorkStealingQueue._nextQueue == null && currentThreadWorkStealingQueue == _workStealingQueues)
				{
					return true;
				}
			}
			bool lockTaken = false;
			try
			{
				FreezeBag(ref lockTaken);
				for (WorkStealingQueue workStealingQueue = _workStealingQueues; workStealingQueue != null; workStealingQueue = workStealingQueue._nextQueue)
				{
					if (!workStealingQueue.IsEmpty)
					{
						return false;
					}
				}
			}
			finally
			{
				UnfreezeBag(lockTaken);
			}
			return true;
		}
	}
 
	bool ICollection.IsSynchronized => false;
 
	object ICollection.SyncRoot
	{
		get
		{
			throw new NotSupportedException(System.SR.ConcurrentCollection_SyncRoot_NotSupported);
		}
	}
 
	private object GlobalQueuesLock => _locals;
 
	public ConcurrentBag()
	{
		_locals = new ThreadLocal<WorkStealingQueue>();
	}
 
	public ConcurrentBag(IEnumerable<T> collection)
	{
		if (collection == null)
		{
			throw new ArgumentNullException("collection", System.SR.ConcurrentBag_Ctor_ArgumentNullException);
		}
		_locals = new ThreadLocal<WorkStealingQueue>();
		WorkStealingQueue currentThreadWorkStealingQueue = GetCurrentThreadWorkStealingQueue(forceCreate: true);
		foreach (T item in collection)
		{
			currentThreadWorkStealingQueue.LocalPush(item, ref _emptyToNonEmptyListTransitionCount);
		}
	}
 
	public void Add(T item)
	{
		GetCurrentThreadWorkStealingQueue(forceCreate: true).LocalPush(item, ref _emptyToNonEmptyListTransitionCount);
	}
 
	bool IProducerConsumerCollection<T>.TryAdd(T item)
	{
		Add(item);
		return true;
	}
 
	public bool TryTake([MaybeNullWhen(false)] out T result)
	{
		WorkStealingQueue currentThreadWorkStealingQueue = GetCurrentThreadWorkStealingQueue(forceCreate: false);
		if (currentThreadWorkStealingQueue == null || !currentThreadWorkStealingQueue.TryLocalPop(out result))
		{
			return TrySteal(out result, take: true);
		}
		return true;
	}
 
	public bool TryPeek([MaybeNullWhen(false)] out T result)
	{
		WorkStealingQueue currentThreadWorkStealingQueue = GetCurrentThreadWorkStealingQueue(forceCreate: false);
		if (currentThreadWorkStealingQueue == null || !currentThreadWorkStealingQueue.TryLocalPeek(out result))
		{
			return TrySteal(out result, take: false);
		}
		return true;
	}
 
	private WorkStealingQueue GetCurrentThreadWorkStealingQueue(bool forceCreate)
	{
		WorkStealingQueue workStealingQueue = _locals.Value;
		if (workStealingQueue == null)
		{
			if (!forceCreate)
			{
				return null;
			}
			workStealingQueue = CreateWorkStealingQueueForCurrentThread();
		}
		return workStealingQueue;
	}
 
	private WorkStealingQueue CreateWorkStealingQueueForCurrentThread()
	{
		lock (GlobalQueuesLock)
		{
			WorkStealingQueue workStealingQueues = _workStealingQueues;
			WorkStealingQueue workStealingQueue = ((workStealingQueues != null) ? GetUnownedWorkStealingQueue() : null);
			if (workStealingQueue == null)
			{
				workStealingQueue = (_workStealingQueues = new WorkStealingQueue(workStealingQueues));
			}
			_locals.Value = workStealingQueue;
			return workStealingQueue;
		}
	}
 
	private WorkStealingQueue GetUnownedWorkStealingQueue()
	{
		int currentManagedThreadId = Environment.CurrentManagedThreadId;
		for (WorkStealingQueue workStealingQueue = _workStealingQueues; workStealingQueue != null; workStealingQueue = workStealingQueue._nextQueue)
		{
			if (workStealingQueue._ownerThreadId == currentManagedThreadId)
			{
				return workStealingQueue;
			}
		}
		return null;
	}
 
	private bool TrySteal([MaybeNullWhen(false)] out T result, bool take)
	{
		if (CDSCollectionETWBCLProvider.Log.IsEnabled())
		{
			if (take)
			{
				CDSCollectionETWBCLProvider.Log.ConcurrentBag_TryTakeSteals();
			}
			else
			{
				CDSCollectionETWBCLProvider.Log.ConcurrentBag_TryPeekSteals();
			}
		}
		while (true)
		{
			long num = Interlocked.Read(ref _emptyToNonEmptyListTransitionCount);
			WorkStealingQueue currentThreadWorkStealingQueue = GetCurrentThreadWorkStealingQueue(forceCreate: false);
			bool num2;
			if (currentThreadWorkStealingQueue != null)
			{
				if (TryStealFromTo(currentThreadWorkStealingQueue._nextQueue, null, out result, take))
				{
					goto IL_0078;
				}
				num2 = TryStealFromTo(_workStealingQueues, currentThreadWorkStealingQueue, out result, take);
			}
			else
			{
				num2 = TryStealFromTo(_workStealingQueues, null, out result, take);
			}
			if (!num2)
			{
				if (Interlocked.Read(ref _emptyToNonEmptyListTransitionCount) == num)
				{
					break;
				}
				continue;
			}
			goto IL_0078;
			IL_0078:
			return true;
		}
		return false;
	}
 
	private bool TryStealFromTo(WorkStealingQueue startInclusive, WorkStealingQueue endExclusive, [MaybeNullWhen(false)] out T result, bool take)
	{
		for (WorkStealingQueue workStealingQueue = startInclusive; workStealingQueue != endExclusive; workStealingQueue = workStealingQueue._nextQueue)
		{
			if (workStealingQueue.TrySteal(out result, take))
			{
				return true;
			}
		}
		result = default(T);
		return false;
	}
 
	public void CopyTo(T[] array, int index)
	{
		if (array == null)
		{
			throw new ArgumentNullException("array", System.SR.ConcurrentBag_CopyTo_ArgumentNullException);
		}
		if (index < 0)
		{
			throw new ArgumentOutOfRangeException("index", System.SR.Collection_CopyTo_ArgumentOutOfRangeException);
		}
		if (_workStealingQueues == null)
		{
			return;
		}
		bool lockTaken = false;
		try
		{
			FreezeBag(ref lockTaken);
			int dangerousCount = DangerousCount;
			if (index > array.Length - dangerousCount)
			{
				throw new ArgumentException(System.SR.Collection_CopyTo_TooManyElems, "index");
			}
			try
			{
				int num = CopyFromEachQueueToArray(array, index);
			}
			catch (ArrayTypeMismatchException ex)
			{
				throw new InvalidCastException(ex.Message, ex);
			}
		}
		finally
		{
			UnfreezeBag(lockTaken);
		}
	}
 
	private int CopyFromEachQueueToArray(T[] array, int index)
	{
		int num = index;
		for (WorkStealingQueue workStealingQueue = _workStealingQueues; workStealingQueue != null; workStealingQueue = workStealingQueue._nextQueue)
		{
			num += workStealingQueue.DangerousCopyTo(array, num);
		}
		return num - index;
	}
 
	void ICollection.CopyTo(Array array, int index)
	{
		if (array is T[] array2)
		{
			CopyTo(array2, index);
			return;
		}
		if (array == null)
		{
			throw new ArgumentNullException("array", System.SR.ConcurrentBag_CopyTo_ArgumentNullException);
		}
		ToArray().CopyTo(array, index);
	}
 
	public T[] ToArray()
	{
		if (_workStealingQueues != null)
		{
			bool lockTaken = false;
			try
			{
				FreezeBag(ref lockTaken);
				int dangerousCount = DangerousCount;
				if (dangerousCount > 0)
				{
					T[] array = new T[dangerousCount];
					int num = CopyFromEachQueueToArray(array, 0);
					return array;
				}
			}
			finally
			{
				UnfreezeBag(lockTaken);
			}
		}
		return Array.Empty<T>();
	}
 
	public void Clear()
	{
		if (_workStealingQueues == null)
		{
			return;
		}
		WorkStealingQueue currentThreadWorkStealingQueue = GetCurrentThreadWorkStealingQueue(forceCreate: false);
		if (currentThreadWorkStealingQueue != null)
		{
			currentThreadWorkStealingQueue.LocalClear();
			if (currentThreadWorkStealingQueue._nextQueue == null && currentThreadWorkStealingQueue == _workStealingQueues)
			{
				return;
			}
		}
		bool lockTaken = false;
		try
		{
			FreezeBag(ref lockTaken);
			for (WorkStealingQueue workStealingQueue = _workStealingQueues; workStealingQueue != null; workStealingQueue = workStealingQueue._nextQueue)
			{
				T result;
				while (workStealingQueue.TrySteal(out result, take: true))
				{
				}
			}
		}
		finally
		{
			UnfreezeBag(lockTaken);
		}
	}
 
	public IEnumerator<T> GetEnumerator()
	{
		return new Enumerator(ToArray());
	}
 
	IEnumerator IEnumerable.GetEnumerator()
	{
		return GetEnumerator();
	}
 
	private void FreezeBag(ref bool lockTaken)
	{
		Monitor.Enter(GlobalQueuesLock, ref lockTaken);
		WorkStealingQueue workStealingQueues = _workStealingQueues;
		for (WorkStealingQueue workStealingQueue = workStealingQueues; workStealingQueue != null; workStealingQueue = workStealingQueue._nextQueue)
		{
			Monitor.Enter(workStealingQueue, ref workStealingQueue._frozen);
		}
		Interlocked.MemoryBarrier();
		for (WorkStealingQueue workStealingQueue2 = workStealingQueues; workStealingQueue2 != null; workStealingQueue2 = workStealingQueue2._nextQueue)
		{
			if (workStealingQueue2._currentOp != 0)
			{
				SpinWait spinWait = default(SpinWait);
				do
				{
					spinWait.SpinOnce();
				}
				while (workStealingQueue2._currentOp != 0);
			}
		}
	}
 
	private void UnfreezeBag(bool lockTaken)
	{
		if (!lockTaken)
		{
			return;
		}
		for (WorkStealingQueue workStealingQueue = _workStealingQueues; workStealingQueue != null; workStealingQueue = workStealingQueue._nextQueue)
		{
			if (workStealingQueue._frozen)
			{
				workStealingQueue._frozen = false;
				Monitor.Exit(workStealingQueue);
			}
		}
		Monitor.Exit(GlobalQueuesLock);
	}
}

2、属性

Count

获取 ConcurrentBag<T> 中包含的元素数

IsEmpty

获取一个值，该值指示 ConcurrentBag<T> 是否为空

3、方法

Add(T)

将对象添加到 ConcurrentBag<T> 中。

Clear()

从 ConcurrentBag<T> 中删除所有值。

CopyTo(T[], Int32)

从指定数组索引开始将 ConcurrentBag<T> 元素复制到现有一维 Array 中。以下示例代码：

 ConcurrentBag<TempModel> tempModels = new ConcurrentBag<TempModel>();
tempModels.Add(new TempModel() { Code = "1", Name = "一" });
tempModels.Add(new TempModel() { Code = "2", Name = "二" });
tempModels.Add(new TempModel() { Code = "3", Name = "三" });
TempModel[] temparr = new TempModel[5];
tempModels.CopyTo(temparr, 1);

输出结果为：

TryPeek(T)

尝试从 ConcurrentBag<T> 返回一个对象但不移除该对象。

TryTake(T)

尝试从 ConcurrentBag<T> 中移除和返回一个对象。

ToString()

返回表示当前对象的字符串。测试值：System.Collections.Concurrent.ConcurrentBag`1[Test.ConsoleApp.TempModel]

ToArray()

将 ConcurrentBag<T> 元素复制到新数组。

GetEnumerator()

获取当前时间的枚举器。调用后不影响集合的任何更新。枚举器可以安全地与读取、写入 ConcurrentBag<T> 同时使用。

GetHashCode()

获取集合的哈希值。

参考：https://learn.microsoft.com/zh-cn/dotnet/api/system.collections.concurrent.concurrentbag-1?view=net-5.0

C# ConcurrentBag的实现原理

4、List<T> 和 ConcurrentBag<T> 对比

众所周知，List<T> 集合是非线程安全的，所以我们采用并行编程时会发生丢数据的情况。比如我们通过多线程将一千个对象加入 List<T>，我们最终得到的集合中元素数就会小于一千。

如下测试代码，通过多任务对象 Task 实现将一千个对象加入到 List<T> 中，添加了一千次，但实际上最终的 objects.Count() 值为 913，小于 1000。但如果将集合名称改成 ConcurrentBag<T>，结果就不会丢失，最终为等于 1000。

 static void Main(string[] args)
{
    try
    {
        // List<MyObject> objects = new List<MyObject>();
        ConcurrentBag<MyObject> objects = new ConcurrentBag<MyObject>();
        Task[] tasks = new Task[1000];
        for (int i = 0; i < 1000; i++)
        {
            tasks[i] = Task.Run(() => 
                objects.Add(new MyObject() { Name = "1", Threadnum = Thread.GetCurrentProcessorId() }));
        }
        Task.WaitAll(tasks); // 等待所有任务完成
        Console.WriteLine(objects.Count()); // List<T>：913； ConcurrentBag<T>：1000
        Console.ReadLine();
    }
    catch (Exception ex)
    {
    }
}
public class MyObject
{
    public string Name { get; set; }
    public int Threadnum { get; set; }
}

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二、Parallel 的使用

任务并行库（TPL）支持通过 System.Threading.Tasks.Parallel 类实现数据操作的并行。Parallel.For 或 Parallel.ForEach 编写的循环逻辑与常见的 for 和 foreach 类似，只是增加并行逻辑，来提升效率。TPL 省去了客户端创建线程或列工作项，同时在基本循环中，不需要加锁，TPL 会处理所有低级别的工作。

常用的方法有 Parallel.For、Parallel.ForEach、Parallel.Invoke 等，下面将一一例举。

1、Parallel.For()

1.1 重载一：Parallel.For(Int32, Int32, Action<Int32>)

 // fromInclusive：开始索引（含） toExclusive：结束索引（不含） body：不允许为 null
public static System.Threading.Tasks.ParallelLoopResult For (int fromInclusive, int toExclusive, Action<int> body);

以下示例使用 For 方法调用 100 个委托，该委托生成随机 Byte 值，并计算其总和：

 ParallelLoopResult result = Parallel.For(0, 100,
    ctr =>
    {
        //Random rnd = new Random(ctr * 100000); // public Random(int Seed); // 随机数的种子，若种子相同，多次生成的随机数序列值相同
        Random rnd = new Random();
        Byte[] bytes = new Byte[100]; // Byte 数组，每个值的范围为 0~255
        rnd.NextBytes(bytes); // 生成 100 个 Byte 数值
        int sum = 0;
        foreach (var byt in bytes) // 再将生成的 100 个数值相加
            sum += byt;
        Console.WriteLine("Iteration {0,2}: {1:N0}", ctr, sum);
    });
Console.WriteLine("Result: Completed Normally");

1.2 比较执行效率 Parallel.For() 和 for()

Paraller.For() 方法类似于 for 循环语句，也是根据入参多次执行同一逻辑操作。使用 Paraller.For() 方法，可以无序的并行运行迭代，而 for 循环只能根据既定的顺序串行运行。

如下实例，对比 Parallel.For() 和 for() 循环的执行效率进行比较：

 // 进行 5 此对比
for (int j = 1; j < 6; j++)
{
    // for()
    Console.WriteLine($"\n第{j}次比较");
    ConcurrentBag<int> bag = new ConcurrentBag<int>();
    var watch = Stopwatch.StartNew();
    watch.Start();
    for (int i = 0; i < 20000000; i++)
    {
        bag.Add(i);
    }
    watch.Stop();
    Console.WriteLine($"串行计算：集合有:{bag.Count},总共耗时：{watch.ElapsedMilliseconds}");
 
    // Parallel.For()
    bag = new ConcurrentBag<int>();
    watch = Stopwatch.StartNew();
    watch.Start();
    Parallel.For(0, 20000000, i => // i 为整数序列号
                 {
                     bag.Add(i);
                 });
    watch.Stop();
    Console.WriteLine($"并行计算：集合有:{bag.Count},总共耗时：{watch.ElapsedMilliseconds}");
}

代码总共执行了五次对比，如下图中的耗时比较，很明显，采用并行的 Parallel.For() 远比串行的 for() 效率要高许多。

1.3 重载二：Parallel.For(Int32, Int32, Action<Int32,ParallelLoopState>)

 // fromInclusive：开始索引（含） toExclusive：结束索引（不含） body：不允许为 null
public static ParallelLoopResult For (int fromInclusive, int toExclusive, Action<int, ParallelLoopState> body);

此重载增加了 System.Threading.Tasks.ParallelLoopState 循环状态参数，从而使得我们可以通过循环状态来控制并行循环的运行。

以下实例，执行 100 次迭代，在随机数 breakIndex 指示的一次迭代时进行中断操作，调用完 Break() 方法后，循环状态的 ShouldExitCurrentIteration 属性值就是 true，然后进入判断if (state.LowestBreakIteration < i)，当当前迭代序号大于中断时的序号，就直接返回，不再进行后续操作。

 var rnd = new Random();
int breakIndex = rnd.Next(1, 11);
Console.WriteLine($"迭代中断的索引值 {breakIndex}\n");
var result = Parallel.For(1, 101, (i, state) => // 实际执行的是 1 ~ 100，不包含 101
{
    Console.WriteLine($"开始迭代-- {i}    {Thread.GetCurrentProcessorId()}");
    int delay;
    lock (rnd)
        delay = rnd.Next(1, 1001);
    Thread.Sleep(delay);
    if (state.ShouldExitCurrentIteration)
    {
        if (state.LowestBreakIteration < i)
            return;
    }
    if (i == breakIndex) // 8
    {
        Console.WriteLine($"在第几次迭代中断 {i}");
        state.Break();
    }
    Console.WriteLine($"迭代完成++ {i}    {Thread.GetCurrentProcessorId()}");
});
if (result.LowestBreakIteration.HasValue)
    Console.WriteLine($"\n最低的迭代中断位置: {result.LowestBreakIteration}");
else
    Console.WriteLine($"\n没有发生最低迭代中断。");

如下是当索引值为 9 时的处理过程：（当迭代序号为 9 时，执行 Break()，此之前已经开始迭代执行的大于 9 的迭代，均直接退出，只有开始没有结束）

通过循环状态 ParallelLoopState 实现两种退出循环的方式：

 // Stop()：满足条件就退出整个 for 循环
if (condittion)
{
    parallelLoopState.Stop();
    return;
}
// Break()：满足条件就退出当次循环，而非跳出整个 for 循环
if (condittion)
{
    parallelLoopState.Break();
    return;
}

1.4 重载三：Parallel.For(Int32, Int32, ParallelOptions, Action<Int32,ParallelLoopState>)

 // fromInclusive：开始索引（含） toExclusive：结束索引（不含） body：不允许为 null
public static ParallelLoopResult For (int fromInclusive, int toExclusive, ParallelOptions parallelOptions, Action<int, ParallelLoopState> body);

此重载在执行 for 循环时，可以配置循环选项 ParallelOptions。

下边是一个实例，通过配置 ParallelOptions 的 CancellationToken 属性，使得循环支持手动取消：

 static void Main(string[] args)
{
    CancellationTokenSource cancellationSource = new CancellationTokenSource();
    ParallelOptions options = new ParallelOptions();
    options.CancellationToken = cancellationSource.Token;
    try
    {
        ParallelLoopResult loopResult = Parallel.For( 0, 10, options,
                (i, loopState) =>
                {
                    Console.WriteLine("Start Thread={0}, i={1}", Thread.CurrentThread.ManagedThreadId, i);
                    if (i == 5) // 模拟某次迭代执行时，取消循环
                    {
                        cancellationSource.Cancel();
                    }
                    for (int j = 0; j < 10; j++)
                    {
                        Thread.Sleep(1 * 200); // 模拟耗时任务
                        if (loopState.ShouldExitCurrentIteration) // 判断循环是否已经取消执行
                            return;
                    }
                    Console.WriteLine($"Finish Thread={Thread.CurrentThread.ManagedThreadId}, i={i}");
                }
            );
        if (loopResult.IsCompleted)
        {
            Console.WriteLine("All iterations completed successfully. THIS WAS NOT EXPECTED.");
        }
    }
    catch (AggregateException aex) // 注意：AggregateException 为并行中专用的异常信息集合
    {
        Console.WriteLine($"Parallel.For has thrown an AggregateException. THIS WAS NOT EXPECTED.\n{aex}");
        //foreach (var item in aex.InnerExceptions) // 可以通过循环将全部信息记录下来
        //{
        //    Console.WriteLine(item.InnerException.Message + "     " + item.GetType().Name);
        //}
        //aex.Handle(p => // 如果想往上级抛，需要使用 Handle 方法处理一下
        //{
        //    if (p.InnerException.Message == "my god！Exception from childTask1 happend！")
        //        return true;
        //    else
        //        return false; // 返回 false 表示往上继续抛出异常
        //});
    }
    catch (OperationCanceledException ocex) // 专门用于取消循环异常的捕捉
    {
        Console.WriteLine($"An iteration has triggered a cancellation. THIS WAS EXPECTED.\n{ocex}");
    }
    finally
    {
        cancellationSource.Dispose();
    }
}

如下图中的输出，所有迭代任务都未完成，主要是因为耗时操作执行完成之前，循环就取消了，在if (loopState.ShouldExitCurrentIteration)判断时，均为 true 就直接返回了。

1.5 重载四：For<TLocal>(Int32, Int32, ParallelOptions, Func<TLocal>, Func<Int32,ParallelLoopState,TLocal,TLocal>, Action<TLocal>)

 public static ParallelLoopResult For<TLocal> (int fromInclusive, int toExclusive, 
                                              ParallelOptions parallelOptions, 
                                              Func<TLocal> localInit, 
                                              Func<int,ParallelLoopState,TLocal,TLocal> body, 
                                              Action<TLocal> localFinally);

以下示例使用线程局部变量来计算许多冗长操作的结果之和。此示例将并行度限制为 4。

 static void Main(string[] args)
{
    int result = 0;
    int N = 1000000;
    Parallel.For(
        0, N,
        // 限制最多 4 个并行任务
        new ParallelOptions { MaxDegreeOfParallelism = 4 },
        // Func<TLocal> 初始化本地变量，本地变量是线程独立变量
        () => 0,
        // Func<Int32,ParallelLoopState,TLocal,TLocal> 迭代操作
        (i, loop, localState) =>
        {
            for (int ii = 0; ii < 10000; ii++) ;
            return localState + 1;
        },
        localState =>
            Interlocked.Add(ref result, localState)
    );
    Console.WriteLine("实际运算结果： {0}. 目标值： 1000000", result);
    Console.ReadLine();
}

如下图输出结果：

参考：https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.tasks.parallel.for?view=net-7.0

关于 ParallelOptions 详见：https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.tasks.paralleloptions?view=net-7.0

2、Parallel.ForEach()

2.1 重载一：Parallel.ForEach<TSource>(IEnumerable<TSource>, Action<TSource>)

 public static ParallelLoopResult ForEach<TSource> (IEnumerable<TSource> source, Action<TSource> body);

执行 ForEach 操作，在处理关于 IEnumerable 集合的任务时，可并行运行迭代。

如下代码块，简单的将一个整数数组，输出到控制台：

 static void Main(string[] args)
{
    int[] ints = { 11, 12, 13, 14, 15, 16, 17, 18, 19 };
    ParallelLoopResult result = Parallel.ForEach(ints,
        i =>
        {
            Console.WriteLine(i);
        });
    Console.ReadLine();
}

从输出结果看，ForEach 操作是无序的：

2.2 重载二：ForEach<TSource>(IEnumerable<TSource>, ParallelOptions, Action<TSource,ParallelLoopState,Int64>)

 public static ParallelLoopResult ForEach<TSource> (IEnumerable<TSource> source, ParallelOptions parallelOptions, Action<TSource,ParallelLoopState,long> body);

执行具有 64 位索引（标识待循环集合的顺序）的 foreach 操作，其中在 IEnumerable 上可能会并行运行迭代，而且可以配置循环选项，可以监视和操作循环的状态。

如下示例代码，设置并行任务数为 5，在索引为 6 的任务执行过程中中断循环，看下输出结果：

 static void Main(string[] args)
{        
    // 创建一个集合，其中包含一些数字
    var numbers = new int[] { 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 };
    // 使用 ParallelOptions 选项设置并行处理的行为
    var parallelOptions = new ParallelOptions
    {
        MaxDegreeOfParallelism = 5
    };
    Parallel.ForEach(numbers, parallelOptions, (source, loopState, index) => // index：集合中对象的从 0 开始的序号
    {
        // 在此处编写并行处理逻辑
        Console.WriteLine($"开始--Index: {index}, Value: {source}, ThreadId: {Thread.GetCurrentProcessorId()}");
        if (loopState.ShouldExitCurrentIteration)
            return;
        Thread.Sleep(200);
        if (index == 6)
            loopState.Break();
        Console.WriteLine($"结束++Index: {index}, Value: {source}, ThreadId: {Thread.GetCurrentProcessorId()}");
    });
    Console.ReadLine();
}

如下图输出结果，一次性开始 5 个并行任务，当第 6 个任务进入时，中断循环。

由于操作是无序的，所以在中断之前可能索引在 6 之后的已经开始或者已经执行完成，如下图 8、9 已经执行完毕，7尚未执行。

注意，若允许并行的任务数少时，可能 6 之后的任务都还没来得及开始，另外，每次执行的结果不同。

2.3 重载三：Parallel.ForEach<TSource>(Partitioner<TSource>, Action<TSource>)

 public static ParallelLoopResult ForEach<TSource> (System.Collections.Concurrent.Partitioner<TSource> source, Action<TSource> body);

此重载的独到之处，就是可以将数据进行分区，每一个小区内实现串行计算，分区采用 Partitioner.Create() 实现。

 long sum = 0;
long sumtop = 10000000;
Stopwatch sw = Stopwatch.StartNew();
Parallel.ForEach(Partitioner.Create(0, sumtop), (range) =>
{
    long local = 0;
    for (long i = range.Item1; i < range.Item2; i++)
        local += i;
    Interlocked.Add(ref sum, local); // Interlocked：为由多个线程共享的变量提供原子操作 Add()：求和后替换原来的数值，相当于 +=
});
sw.Stop();
Console.WriteLine($"Partitioner.Create() 分区方式执行效率： result = {sum}, time = {sw.ElapsedMilliseconds} ms");
// 输出：
// Partitioner.Create() 分区方式执行效率： result = 49999995000000, time = 8 ms

关于分区的创建方法 Partitioner.Create(0, Int64)

指定了分区的范围，就是 0 ~ Int64；
参数中并没有指定分多少个区，默认是系统自动判断执行的。
还可以指定分区，做法就是Partitioner.Create(0, 3000000, Environment.ProcessorCount)，其中 Environment.ProcessorCount 参数，就对应当前计算机逻辑处理器的数量。

2.4 重载四：ForEach<TSource,TLocal>(IEnumerable<TSource>, Func<TLocal>, Func<TSource,ParallelLoopState,TLocal,TLocal>, Action<TLocal>)

执行具有线程本地数据的 foreach 操作，其中在 IEnumerable 上可能会并行运行迭代，而且可以监视和操作循环的状态。

 public static ParallelLoopResult ForEach<TSource,TLocal> (IEnumerable<TSource> source, 
                                                          Func<TLocal> localInit,
                                                          Func<TSource,ParallelLoopState,TLocal,TLocal> body, 
                                                          Action<TLocal> localFinally);

如下示例，将全部整数逐个输出并且最后在输出他们之和：

 static void Main(string[] args)
{
    // 全部值的和为 40
    int[] input = { 4, 1, 6, 2, 9, 5, 10, 3 };
    int sum = 0;
    try
    {
        Parallel.ForEach(
                // IEnumerable<TSource> 可枚举的数据源
                input,
                // Func<TLocal> 用于返回每个任务的【本地数据的初始状态】的函数委托
                // 本示例中的目的就是将 TLocal localSum 的值在每次迭代都赋值为 0
                () => 0,
                // Func<TSource,ParallelLoopState,TLocal,TLocal> 将为每个迭代调用一次的委托
                (n, loopState, localSum) =>
                {
                    localSum += n;
                    Console.WriteLine($"Thread={Thread.CurrentThread.ManagedThreadId}, n={n}, localSum={localSum}");
                    return localSum;
                },
                // Action<TLocal> 用于对每个任务的本地状态执行一个最终操作的委托
                // 此示例中的作用是将每个值逐一求和，并返回 sum
                (localSum) =>
                    Interlocked.Add(ref sum, localSum)
            );
        Console.WriteLine("\nSum={0}", sum);
    }
    catch (AggregateException e)
    {
        Console.WriteLine("Parallel.ForEach has thrown an exception. This was not expected.\n{0}", e);
    }
    Console.ReadLine();
}

如下输出结果，其中 localSum 在每个线程中初始值都是 0，在其他线程中参与的求和运算，不影响当前线程。

2.5 比较执行效率 for、Parallel.For()、Parallel.For()+TLocal、Parallel.ForEach(Partitioner.Create(), Action<TSource>)

 static void Main(string[] args)
{
    Stopwatch sw = null;
    long sum = 0;
    long sumtop = 10000000;
    // 常规 for 循环
    sw = Stopwatch.StartNew();
    for (long i = 0; i < sumtop; i++)
        sum += i;
    sw.Stop();
    Console.WriteLine($"result = {sum}, time = {sw.ElapsedMilliseconds} ms  --常规 for 循环");
 
    // Parallel.For() 方式
    sum = 0;
    sw = Stopwatch.StartNew();
    Parallel.For(0L, sumtop,
        (item) => Interlocked.Add(ref sum, item));
    sw.Stop();
    Console.WriteLine($"result = {sum}, time = {sw.ElapsedMilliseconds} ms  --Parallel.For() 方式");
 
    // Parallel.For() + TLocal
    sum = 0;
    sw = Stopwatch.StartNew();
    Parallel.For(
        0L, sumtop, 
        () => 0L, 
        (item, state, prevLocal) => 
            prevLocal + item, 
        local => 
            Interlocked.Add(ref sum, local));
    sw.Stop();
    Console.WriteLine($"result = {sum}, time = {sw.ElapsedMilliseconds} ms  --Parallel.For() + locals 方式");
 
    // Partitioner.Create() 分区方式
    sum = 0;
    sw = Stopwatch.StartNew();
    Parallel.ForEach(Partitioner.Create(0L, sumtop), (range) =>
    {
        long local = 0;
        for (long i = range.Item1; i < range.Item2; i++)
            local += i;
        Interlocked.Add(ref sum, local);
    });
    sw.Stop();
    Console.WriteLine($"result = {sum}, time = {sw.ElapsedMilliseconds} ms  --Partitioner.Create() 分区方式");
    Console.ReadLine();
}

如下输出结果，效率最高的显然是自动分区的方式，比常规的 for 循环块将近一倍。最慢的是 Parallel.For() 方式，由于加锁求和导致上下文频繁切换比较耗时，因此这种求和的计算模式不适用。

参考：https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.tasks.parallel.foreach?view=net-7.0

3、Parallel.ForEachAsync()

Parallel.ForEachAsync() 是在 .NET 6 中新增的一个 API，是 Parallel.ForEach() 的异步版本。https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.tasks.parallel.foreachasync?view=net-7.0

下面简单说明一下 Parallel.ForEach() 和 Parallel.ForEachAsync() 的区别。

Parallel.ForEach() 是在默认多个或指定的个数的线程下执行的。而 Parallel.ForEachAsync() 不一定是多线程的，强调的是异步而已。
若目标集合必须按照顺序执行，则不能选用 Parallel.ForEach() 方法，因为它是无序执行的。
当待处理的数据量很大或者执行过程比较耗时，则选用多线程执行的 Parallel.ForEach() 方法更好。

下面是一个关于重载 ForEachAsync<TSource>(IAsyncEnumerable<TSource>, ParallelOptions, Func<TSource,CancellationToken,ValueTask>) 的一个简单示例代码：

 static async Task Main(string[] args)
{
    var nums = Enumerable.Range(0, 10).ToArray();
    await Parallel.ForEachAsync(
        nums,
        new ParallelOptions { MaxDegreeOfParallelism = 3 }, // 配置最多同时分配三个线程
        async (i, token) => // Func<TSource,CancellationToken,ValueTask> // 其中 ValueTask 提供异步操作的可等待结果，指的是下文 await 的内容
        {
            Console.WriteLine($"开始迭代任务 {i} ThreadId:{Thread.GetCurrentProcessorId()}");
            // public static Task Delay(int millisecondsDelay, CancellationToken cancellationToken)
            // 在指定毫秒后，调用 token 取消当前任务
            await Task.Delay(1000, token); 
            Console.WriteLine($"完成迭代任务 {i}");
        });
    Console.WriteLine("Finished!");
    Console.ReadLine();
}

详情可参考：https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.tasks.parallel.foreachasync?view=net-7.0 ； https://www.gregbair.dev/posts/parallel-foreachasync/

4、Parallel.Invoke()

尽可能并行执行提供的每个操作。

4.1 两个重载：Invoke(Action[])、Invoke(ParallelOptions, Action[])

下面是一个运用 Invoke(Action[]) 重载的示例，分别加入了三个操作，然后看执行结果。第二个重载是在第一个重载的基础上加了并行选项 ParallelOptions 就不在赘述了。

 static void Main(string[] args)
{
    try
    {
        Parallel.Invoke(
            BasicAction,	// 第一个操作 - 静态方法
            () =>		// 第二个操作 - 箭头函数
            {
                Console.WriteLine("Method=beta, Thread={0}", Thread.CurrentThread.ManagedThreadId);
            },
            delegate ()		// 第三个操作 - 委托函数
            {
                Console.WriteLine("Method=gamma, Thread={0}", Thread.CurrentThread.ManagedThreadId);
            }
        );
    }
    catch (AggregateException e)
    {
        Console.WriteLine("An action has thrown an exception. THIS WAS UNEXPECTED.\n{0}", e.InnerException.ToString());
    }
    Console.ReadLine();
}
static void BasicAction()
{
    Console.WriteLine("Method=alpha, Thread={0}", Thread.CurrentThread.ManagedThreadId);
}

由输出结果可知，三个操作是无序的、多线程执行的。

两个参考：https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.tasks.parallel.invoke?view=net-7.0 Parallel的使用

回到顶部

三、简单总结一下下

实际上看的资料再多，如果没用到实际开发当中就是无用功，下边简单总结一下吧。

由本文 1.2 比较执行效率 Parallel.For() 和 for() 中可知：

对于大批量耗时且顺序要求不高的场景可以采用 Parallel.For() 方法，如果对次序有依赖，则只能采用常用的 for 循环。
对于操作简单的循环操作，Parallel.For() 就不太适合了，因为多线程操作涉及到上下文的切换，过多的切换场景会严重影响程序运行的效率。

由本文 2.5 比较执行效率 for、Parallel.For()、Parallel.For()+TLocal、Parallel.ForEach(Partitioner.Create(), Action<TSource>) 中可知：

由于示例中的操作比较简单，此时 Parallel.For() 上下文的的切换耗时以及加锁的缺点就凸现了，效率最差。
使用线程本地变量（TLocal）的 Parallel.For() 可以避免将大量的访问同步为共享状态的开销，所以可以看到效率就高很多。可参考：编写具有线程局部变量的 Parallel.For 循环
分区循环操作 Partitioner.Create(0, Int64) 方法的效率最高，因为事先给待处理的任务进行了分区，分区内串行，避免了过多的上下文切换耗时。

注：个人整理，欢迎路过的大佬评论区指正和补充。

posted @ 2023-07-13 18:31 橙子家阅读(1559) 评论(2) 编辑收藏举报

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橙子家

Parallel 与 ConcurrentBag<T> 这对儿黄金搭档（C#）【并发编程系列_2】

〇、前言

一、ConcurrentBag<T> 简介

1、简介与源码

2、属性

3、方法

4、List<T> 和 ConcurrentBag<T> 对比

二、Parallel 的使用

1、Parallel.For()

1.1 重载一：Parallel.For(Int32, Int32, Action<Int32>)

1.2 比较执行效率 Parallel.For() 和 for()

1.3 重载二：Parallel.For(Int32, Int32, Action<Int32,ParallelLoopState>)

1.4 重载三：Parallel.For(Int32, Int32, ParallelOptions, Action<Int32,ParallelLoopState>)

1.5 重载四：For<TLocal>(Int32, Int32, ParallelOptions, Func<TLocal>, Func<Int32,ParallelLoopState,TLocal,TLocal>, Action<TLocal>)

2、Parallel.ForEach()

2.1 重载一：Parallel.ForEach<TSource>(IEnumerable<TSource>, Action<TSource>)

2.2 重载二：ForEach<TSource>(IEnumerable<TSource>, ParallelOptions, Action<TSource,ParallelLoopState,Int64>)

2.3 重载三：Parallel.ForEach<TSource>(Partitioner<TSource>, Action<TSource>)

2.4 重载四：ForEach<TSource,TLocal>(IEnumerable<TSource>, Func<TLocal>, Func<TSource,ParallelLoopState,TLocal,TLocal>, Action<TLocal>)

2.5 比较执行效率 for、Parallel.For()、Parallel.For()+TLocal、Parallel.ForEach(Partitioner.Create(), Action<TSource>)

3、Parallel.ForEachAsync()

4、Parallel.Invoke()

4.1 两个重载：Invoke(Action[])、Invoke(ParallelOptions, Action[])

三、简单总结一下下

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	// System.Collections.Concurrent, Version=5.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
	// System.Collections.Concurrent.ConcurrentBag<T>
	using System;
	using System.Collections;
	using System.Collections.Concurrent;
	using System.Collections.Generic;
	using System.Diagnostics;
	using System.Diagnostics.CodeAnalysis;
	using System.Threading;

	[DebuggerTypeProxy(typeof(System.Collections.Concurrent.IProducerConsumerCollectionDebugView<>))]
	[DebuggerDisplay("Count = {Count}")]
	public class ConcurrentBag<T> : IProducerConsumerCollection<T>, IEnumerable<T>, IEnumerable, ICollection, IReadOnlyCollection<T>
	{
	private sealed class WorkStealingQueue
	{
	private volatile int _headIndex;

	private volatile int _tailIndex;

	private volatile T[] _array = new T[32];

	private volatile int _mask = 31;

	private int _addTakeCount;

	private int _stealCount;

	internal volatile int _currentOp;

	internal bool _frozen;

	internal readonly WorkStealingQueue _nextQueue;

	internal readonly int _ownerThreadId;

	internal bool IsEmpty => _headIndex - _tailIndex >= 0;

	internal int DangerousCount
	{
	get
	{
	int stealCount = _stealCount;
	int addTakeCount = _addTakeCount;
	return addTakeCount - stealCount;
	}
	}

	internal WorkStealingQueue(WorkStealingQueue nextQueue)
	{
	_ownerThreadId = Environment.CurrentManagedThreadId;
	_nextQueue = nextQueue;
	}

	internal void LocalPush(T item, ref long emptyToNonEmptyListTransitionCount)
	{
	bool lockTaken = false;
	try
	{
	Interlocked.Exchange(ref _currentOp, 1);
	int num = _tailIndex;
	if (num == int.MaxValue)
	{
	_currentOp = 0;
	lock (this)
	{
	_headIndex &= _mask;
	num = (_tailIndex = num & _mask);
	Interlocked.Exchange(ref _currentOp, 1);
	}
	}
	int headIndex = _headIndex;
	if (!_frozen && headIndex - (num - 1) < 0 && num - (headIndex + _mask) < 0)
	{
	_array[num & _mask] = item;
	_tailIndex = num + 1;
	}
	else
	{
	_currentOp = 0;
	Monitor.Enter(this, ref lockTaken);
	headIndex = _headIndex;
	int num2 = num - headIndex;
	if (num2 >= _mask)
	{
	T[] array = new T[_array.Length << 1];
	int num3 = headIndex & _mask;
	if (num3 == 0)
	{
	Array.Copy(_array, array, _array.Length);
	}
	else
	{
	Array.Copy(_array, num3, array, 0, _array.Length - num3);
	Array.Copy(_array, 0, array, _array.Length - num3, num3);
	}
	_array = array;
	_headIndex = 0;
	num = (_tailIndex = num2);
	_mask = (_mask << 1) \| 1;
	}
	_array[num & _mask] = item;
	_tailIndex = num + 1;
	if (num2 == 0)
	{
	Interlocked.Increment(ref emptyToNonEmptyListTransitionCount);
	}
	_addTakeCount -= _stealCount;
	_stealCount = 0;
	}
	checked
	{
	_addTakeCount++;
	}
	}
	finally
	{
	_currentOp = 0;
	if (lockTaken)
	{
	Monitor.Exit(this);
	}
	}
	}

	internal void LocalClear()
	{
	lock (this)
	{
	if (_headIndex - _tailIndex < 0)
	{
	_headIndex = (_tailIndex = 0);
	_addTakeCount = (_stealCount = 0);
	Array.Clear(_array, 0, _array.Length);
	}
	}
	}

	internal bool TryLocalPop([MaybeNullWhen(false)] out T result)
	{
	int tailIndex = _tailIndex;
	if (_headIndex - tailIndex >= 0)
	{
	result = default(T);
	return false;
	}
	bool lockTaken = false;
	try
	{
	_currentOp = 2;
	Interlocked.Exchange(ref _tailIndex, --tailIndex);
	if (!_frozen && _headIndex - tailIndex < 0)
	{
	int num = tailIndex & _mask;
	result = _array[num];
	_array[num] = default(T);
	_addTakeCount--;
	return true;
	}
	_currentOp = 0;
	Monitor.Enter(this, ref lockTaken);
	if (_headIndex - tailIndex <= 0)
	{
	int num2 = tailIndex & _mask;
	result = _array[num2];
	_array[num2] = default(T);
	_addTakeCount--;
	return true;
	}
	_tailIndex = tailIndex + 1;
	result = default(T);
	return false;
	}
	finally
	{
	_currentOp = 0;
	if (lockTaken)
	{
	Monitor.Exit(this);
	}
	}
	}

	internal bool TryLocalPeek([MaybeNullWhen(false)] out T result)
	{
	int tailIndex = _tailIndex;
	if (_headIndex - tailIndex < 0)
	{
	lock (this)
	{
	if (_headIndex - tailIndex < 0)
	{
	result = _array[(tailIndex - 1) & _mask];
	return true;
	}
	}
	}
	result = default(T);
	return false;
	}

	internal bool TrySteal([MaybeNullWhen(false)] out T result, bool take)
	{
	lock (this)
	{
	int headIndex = _headIndex;
	if (take)
	{
	if (headIndex - (_tailIndex - 2) >= 0 && _currentOp == 1)
	{
	SpinWait spinWait = default(SpinWait);
	do
	{
	spinWait.SpinOnce();
	}
	while (_currentOp == 1);
	}
	Interlocked.Exchange(ref _headIndex, headIndex + 1);
	if (headIndex < _tailIndex)
	{
	int num = headIndex & _mask;
	result = _array[num];
	_array[num] = default(T);
	_stealCount++;
	return true;
	}
	_headIndex = headIndex;
	}
	else if (headIndex < _tailIndex)
	{
	result = _array[headIndex & _mask];
	return true;
	}
	}
	result = default(T);
	return false;
	}

	internal int DangerousCopyTo(T[] array, int arrayIndex)
	{
	int headIndex = _headIndex;
	int dangerousCount = DangerousCount;
	for (int num = arrayIndex + dangerousCount - 1; num >= arrayIndex; num--)
	{
	array[num] = _array[headIndex++ & _mask];
	}
	return dangerousCount;
	}
	}

	private sealed class Enumerator : IEnumerator<T>, IDisposable, IEnumerator
	{
	private readonly T[] _array;

	private T _current;

	private int _index;

	public T Current => _current;

	object IEnumerator.Current
	{
	get
	{
	if (_index == 0 \|\| _index == _array.Length + 1)
	{
	throw new InvalidOperationException(System.SR.ConcurrentBag_Enumerator_EnumerationNotStartedOrAlreadyFinished);
	}
	return Current;
	}
	}

	public Enumerator(T[] array)
	{
	_array = array;
	}

	public bool MoveNext()
	{
	if (_index < _array.Length)
	{
	_current = _array[_index++];
	return true;
	}
	_index = _array.Length + 1;
	return false;
	}

	public void Reset()
	{
	_index = 0;
	_current = default(T);
	}

	public void Dispose()
	{
	}
	}

	private readonly ThreadLocal<WorkStealingQueue> _locals;

	private volatile WorkStealingQueue _workStealingQueues;

	private long _emptyToNonEmptyListTransitionCount;

	public int Count
	{
	get
	{
	if (_workStealingQueues == null)
	{
	return 0;
	}
	bool lockTaken = false;
	try
	{
	FreezeBag(ref lockTaken);
	return DangerousCount;
	}
	finally
	{
	UnfreezeBag(lockTaken);
	}
	}
	}

	private int DangerousCount
	{
	get
	{
	int num = 0;
	for (WorkStealingQueue workStealingQueue = _workStealingQueues; workStealingQueue != null; workStealingQueue = workStealingQueue._nextQueue)
	{
	num = checked(num + workStealingQueue.DangerousCount);
	}
	return num;
	}
	}

	public bool IsEmpty
	{
	get
	{
	WorkStealingQueue currentThreadWorkStealingQueue = GetCurrentThreadWorkStealingQueue(forceCreate: false);
	if (currentThreadWorkStealingQueue != null)
	{
	if (!currentThreadWorkStealingQueue.IsEmpty)
	{
	return false;
	}
	if (currentThreadWorkStealingQueue._nextQueue == null && currentThreadWorkStealingQueue == _workStealingQueues)
	{
	return true;
	}
	}
	bool lockTaken = false;
	try
	{
	FreezeBag(ref lockTaken);
	for (WorkStealingQueue workStealingQueue = _workStealingQueues; workStealingQueue != null; workStealingQueue = workStealingQueue._nextQueue)
	{
	if (!workStealingQueue.IsEmpty)
	{
	return false;
	}
	}
	}
	finally
	{
	UnfreezeBag(lockTaken);
	}
	return true;
	}
	}

	bool ICollection.IsSynchronized => false;

	object ICollection.SyncRoot
	{
	get
	{
	throw new NotSupportedException(System.SR.ConcurrentCollection_SyncRoot_NotSupported);
	}
	}

	private object GlobalQueuesLock => _locals;

	public ConcurrentBag()
	{
	_locals = new ThreadLocal<WorkStealingQueue>();
	}

	public ConcurrentBag(IEnumerable<T> collection)
	{
	if (collection == null)
	{
	throw new ArgumentNullException("collection", System.SR.ConcurrentBag_Ctor_ArgumentNullException);
	}
	_locals = new ThreadLocal<WorkStealingQueue>();
	WorkStealingQueue currentThreadWorkStealingQueue = GetCurrentThreadWorkStealingQueue(forceCreate: true);
	foreach (T item in collection)
	{
	currentThreadWorkStealingQueue.LocalPush(item, ref _emptyToNonEmptyListTransitionCount);
	}
	}

	public void Add(T item)
	{
	GetCurrentThreadWorkStealingQueue(forceCreate: true).LocalPush(item, ref _emptyToNonEmptyListTransitionCount);
	}

	bool IProducerConsumerCollection<T>.TryAdd(T item)
	{
	Add(item);
	return true;
	}

	public bool TryTake([MaybeNullWhen(false)] out T result)
	{
	WorkStealingQueue currentThreadWorkStealingQueue = GetCurrentThreadWorkStealingQueue(forceCreate: false);
	if (currentThreadWorkStealingQueue == null \|\| !currentThreadWorkStealingQueue.TryLocalPop(out result))
	{
	return TrySteal(out result, take: true);
	}
	return true;
	}

	public bool TryPeek([MaybeNullWhen(false)] out T result)
	{
	WorkStealingQueue currentThreadWorkStealingQueue = GetCurrentThreadWorkStealingQueue(forceCreate: false);
	if (currentThreadWorkStealingQueue == null \|\| !currentThreadWorkStealingQueue.TryLocalPeek(out result))
	{
	return TrySteal(out result, take: false);
	}
	return true;
	}

	private WorkStealingQueue GetCurrentThreadWorkStealingQueue(bool forceCreate)
	{
	WorkStealingQueue workStealingQueue = _locals.Value;
	if (workStealingQueue == null)
	{
	if (!forceCreate)
	{
	return null;
	}
	workStealingQueue = CreateWorkStealingQueueForCurrentThread();
	}
	return workStealingQueue;
	}

	private WorkStealingQueue CreateWorkStealingQueueForCurrentThread()
	{
	lock (GlobalQueuesLock)
	{
	WorkStealingQueue workStealingQueues = _workStealingQueues;
	WorkStealingQueue workStealingQueue = ((workStealingQueues != null) ? GetUnownedWorkStealingQueue() : null);
	if (workStealingQueue == null)
	{
	workStealingQueue = (_workStealingQueues = new WorkStealingQueue(workStealingQueues));
	}
	_locals.Value = workStealingQueue;
	return workStealingQueue;
	}
	}

	private WorkStealingQueue GetUnownedWorkStealingQueue()
	{
	int currentManagedThreadId = Environment.CurrentManagedThreadId;
	for (WorkStealingQueue workStealingQueue = _workStealingQueues; workStealingQueue != null; workStealingQueue = workStealingQueue._nextQueue)
	{
	if (workStealingQueue._ownerThreadId == currentManagedThreadId)
	{
	return workStealingQueue;
	}
	}
	return null;
	}

	private bool TrySteal([MaybeNullWhen(false)] out T result, bool take)
	{
	if (CDSCollectionETWBCLProvider.Log.IsEnabled())
	{
	if (take)
	{
	CDSCollectionETWBCLProvider.Log.ConcurrentBag_TryTakeSteals();
	}
	else
	{
	CDSCollectionETWBCLProvider.Log.ConcurrentBag_TryPeekSteals();
	}
	}
	while (true)
	{
	long num = Interlocked.Read(ref _emptyToNonEmptyListTransitionCount);
	WorkStealingQueue currentThreadWorkStealingQueue = GetCurrentThreadWorkStealingQueue(forceCreate: false);
	bool num2;
	if (currentThreadWorkStealingQueue != null)
	{
	if (TryStealFromTo(currentThreadWorkStealingQueue._nextQueue, null, out result, take))
	{
	goto IL_0078;
	}
	num2 = TryStealFromTo(_workStealingQueues, currentThreadWorkStealingQueue, out result, take);
	}
	else
	{
	num2 = TryStealFromTo(_workStealingQueues, null, out result, take);
	}
	if (!num2)
	{
	if (Interlocked.Read(ref _emptyToNonEmptyListTransitionCount) == num)
	{
	break;
	}
	continue;
	}
	goto IL_0078;
	IL_0078:
	return true;
	}
	return false;
	}

	private bool TryStealFromTo(WorkStealingQueue startInclusive, WorkStealingQueue endExclusive, [MaybeNullWhen(false)] out T result, bool take)
	{
	for (WorkStealingQueue workStealingQueue = startInclusive; workStealingQueue != endExclusive; workStealingQueue = workStealingQueue._nextQueue)
	{
	if (workStealingQueue.TrySteal(out result, take))
	{
	return true;
	}
	}
	result = default(T);
	return false;
	}

	public void CopyTo(T[] array, int index)
	{
	if (array == null)
	{
	throw new ArgumentNullException("array", System.SR.ConcurrentBag_CopyTo_ArgumentNullException);
	}
	if (index < 0)
	{
	throw new ArgumentOutOfRangeException("index", System.SR.Collection_CopyTo_ArgumentOutOfRangeException);
	}
	if (_workStealingQueues == null)
	{
	return;
	}
	bool lockTaken = false;
	try
	{
	FreezeBag(ref lockTaken);
	int dangerousCount = DangerousCount;
	if (index > array.Length - dangerousCount)
	{
	throw new ArgumentException(System.SR.Collection_CopyTo_TooManyElems, "index");
	}
	try
	{
	int num = CopyFromEachQueueToArray(array, index);
	}
	catch (ArrayTypeMismatchException ex)
	{
	throw new InvalidCastException(ex.Message, ex);
	}
	}
	finally
	{
	UnfreezeBag(lockTaken);
	}
	}

	private int CopyFromEachQueueToArray(T[] array, int index)
	{
	int num = index;
	for (WorkStealingQueue workStealingQueue = _workStealingQueues; workStealingQueue != null; workStealingQueue = workStealingQueue._nextQueue)
	{
	num += workStealingQueue.DangerousCopyTo(array, num);
	}
	return num - index;
	}

	void ICollection.CopyTo(Array array, int index)
	{
	if (array is T[] array2)
	{
	CopyTo(array2, index);
	return;
	}
	if (array == null)
	{
	throw new ArgumentNullException("array", System.SR.ConcurrentBag_CopyTo_ArgumentNullException);
	}
	ToArray().CopyTo(array, index);
	}

	public T[] ToArray()
	{
	if (_workStealingQueues != null)
	{
	bool lockTaken = false;
	try
	{
	FreezeBag(ref lockTaken);
	int dangerousCount = DangerousCount;
	if (dangerousCount > 0)
	{
	T[] array = new T[dangerousCount];
	int num = CopyFromEachQueueToArray(array, 0);
	return array;
	}
	}
	finally
	{
	UnfreezeBag(lockTaken);
	}
	}
	return Array.Empty<T>();
	}

	public void Clear()
	{
	if (_workStealingQueues == null)
	{
	return;
	}
	WorkStealingQueue currentThreadWorkStealingQueue = GetCurrentThreadWorkStealingQueue(forceCreate: false);
	if (currentThreadWorkStealingQueue != null)
	{
	currentThreadWorkStealingQueue.LocalClear();
	if (currentThreadWorkStealingQueue._nextQueue == null && currentThreadWorkStealingQueue == _workStealingQueues)
	{
	return;
	}
	}
	bool lockTaken = false;
	try
	{
	FreezeBag(ref lockTaken);
	for (WorkStealingQueue workStealingQueue = _workStealingQueues; workStealingQueue != null; workStealingQueue = workStealingQueue._nextQueue)
	{
	T result;
	while (workStealingQueue.TrySteal(out result, take: true))
	{
	}
	}
	}
	finally
	{
	UnfreezeBag(lockTaken);
	}
	}

	public IEnumerator<T> GetEnumerator()
	{
	return new Enumerator(ToArray());
	}

	IEnumerator IEnumerable.GetEnumerator()
	{
	return GetEnumerator();
	}

	private void FreezeBag(ref bool lockTaken)
	{
	Monitor.Enter(GlobalQueuesLock, ref lockTaken);
	WorkStealingQueue workStealingQueues = _workStealingQueues;
	for (WorkStealingQueue workStealingQueue = workStealingQueues; workStealingQueue != null; workStealingQueue = workStealingQueue._nextQueue)
	{
	Monitor.Enter(workStealingQueue, ref workStealingQueue._frozen);
	}
	Interlocked.MemoryBarrier();
	for (WorkStealingQueue workStealingQueue2 = workStealingQueues; workStealingQueue2 != null; workStealingQueue2 = workStealingQueue2._nextQueue)
	{
	if (workStealingQueue2._currentOp != 0)
	{
	SpinWait spinWait = default(SpinWait);
	do
	{
	spinWait.SpinOnce();
	}
	while (workStealingQueue2._currentOp != 0);
	}
	}
	}

	private void UnfreezeBag(bool lockTaken)
	{
	if (!lockTaken)
	{
	return;
	}
	for (WorkStealingQueue workStealingQueue = _workStealingQueues; workStealingQueue != null; workStealingQueue = workStealingQueue._nextQueue)
	{
	if (workStealingQueue._frozen)
	{
	workStealingQueue._frozen = false;
	Monitor.Exit(workStealingQueue);
	}
	}
	Monitor.Exit(GlobalQueuesLock);
	}
	}

	ConcurrentBag<TempModel> tempModels = new ConcurrentBag<TempModel>();
	tempModels.Add(new TempModel() { Code = "1", Name = "一" });
	tempModels.Add(new TempModel() { Code = "2", Name = "二" });
	tempModels.Add(new TempModel() { Code = "3", Name = "三" });
	TempModel[] temparr = new TempModel[5];
	tempModels.CopyTo(temparr, 1);

	static void Main(string[] args)
	{
	try
	{
	// List<MyObject> objects = new List<MyObject>();
	ConcurrentBag<MyObject> objects = new ConcurrentBag<MyObject>();
	Task[] tasks = new Task[1000];
	for (int i = 0; i < 1000; i++)
	{
	tasks[i] = Task.Run(() =>
	objects.Add(new MyObject() { Name = "1", Threadnum = Thread.GetCurrentProcessorId() }));
	}
	Task.WaitAll(tasks); // 等待所有任务完成
	Console.WriteLine(objects.Count()); // List<T>：913； ConcurrentBag<T>：1000
	Console.ReadLine();
	}
	catch (Exception ex)
	{
	}
	}
	public class MyObject
	{
	public string Name { get; set; }
	public int Threadnum { get; set; }
	}

	// fromInclusive：开始索引（含） toExclusive：结束索引（不含） body：不允许为 null
	public static System.Threading.Tasks.ParallelLoopResult For (int fromInclusive, int toExclusive, Action<int> body);

	ParallelLoopResult result = Parallel.For(0, 100,
	ctr =>
	{
	//Random rnd = new Random(ctr * 100000); // public Random(int Seed); // 随机数的种子，若种子相同，多次生成的随机数序列值相同
	Random rnd = new Random();
	Byte[] bytes = new Byte[100]; // Byte 数组，每个值的范围为 0~255
	rnd.NextBytes(bytes); // 生成 100 个 Byte 数值
	int sum = 0;
	foreach (var byt in bytes) // 再将生成的 100 个数值相加
	sum += byt;
	Console.WriteLine("Iteration {0,2}: {1:N0}", ctr, sum);
	});
	Console.WriteLine("Result: Completed Normally");

	// 进行 5 此对比
	for (int j = 1; j < 6; j++)
	{
	// for()
	Console.WriteLine($"\n第{j}次比较");
	ConcurrentBag<int> bag = new ConcurrentBag<int>();
	var watch = Stopwatch.StartNew();
	watch.Start();
	for (int i = 0; i < 20000000; i++)
	{
	bag.Add(i);
	}
	watch.Stop();
	Console.WriteLine($"串行计算：集合有:{bag.Count},总共耗时：{watch.ElapsedMilliseconds}");

	// Parallel.For()
	bag = new ConcurrentBag<int>();
	watch = Stopwatch.StartNew();
	watch.Start();
	Parallel.For(0, 20000000, i => // i 为整数序列号
	{
	bag.Add(i);
	});
	watch.Stop();
	Console.WriteLine($"并行计算：集合有:{bag.Count},总共耗时：{watch.ElapsedMilliseconds}");
	}

	// fromInclusive：开始索引（含） toExclusive：结束索引（不含） body：不允许为 null
	public static ParallelLoopResult For (int fromInclusive, int toExclusive, Action<int, ParallelLoopState> body);

	var rnd = new Random();
	int breakIndex = rnd.Next(1, 11);
	Console.WriteLine($"迭代中断的索引值 {breakIndex}\n");
	var result = Parallel.For(1, 101, (i, state) => // 实际执行的是 1 ~ 100，不包含 101
	{
	Console.WriteLine($"开始迭代-- {i} {Thread.GetCurrentProcessorId()}");
	int delay;
	lock (rnd)
	delay = rnd.Next(1, 1001);
	Thread.Sleep(delay);
	if (state.ShouldExitCurrentIteration)
	{
	if (state.LowestBreakIteration < i)
	return;
	}
	if (i == breakIndex) // 8
	{
	Console.WriteLine($"在第几次迭代中断 {i}");
	state.Break();
	}
	Console.WriteLine($"迭代完成++ {i} {Thread.GetCurrentProcessorId()}");
	});
	if (result.LowestBreakIteration.HasValue)
	Console.WriteLine($"\n最低的迭代中断位置: {result.LowestBreakIteration}");
	else
	Console.WriteLine($"\n没有发生最低迭代中断。");

	// Stop()：满足条件就退出整个 for 循环
	if (condittion)
	{
	parallelLoopState.Stop();
	return;
	}
	// Break()：满足条件就退出当次循环，而非跳出整个 for 循环
	if (condittion)
	{
	parallelLoopState.Break();
	return;
	}

	static void Main(string[] args)
	{
	CancellationTokenSource cancellationSource = new CancellationTokenSource();
	ParallelOptions options = new ParallelOptions();
	options.CancellationToken = cancellationSource.Token;
	try
	{
	ParallelLoopResult loopResult = Parallel.For( 0, 10, options,
	(i, loopState) =>
	{
	Console.WriteLine("Start Thread={0}, i={1}", Thread.CurrentThread.ManagedThreadId, i);
	if (i == 5) // 模拟某次迭代执行时，取消循环
	{
	cancellationSource.Cancel();
	}
	for (int j = 0; j < 10; j++)
	{
	Thread.Sleep(1 * 200); // 模拟耗时任务
	if (loopState.ShouldExitCurrentIteration) // 判断循环是否已经取消执行
	return;
	}
	Console.WriteLine($"Finish Thread={Thread.CurrentThread.ManagedThreadId}, i={i}");
	}
	);
	if (loopResult.IsCompleted)
	{
	Console.WriteLine("All iterations completed successfully. THIS WAS NOT EXPECTED.");
	}
	}
	catch (AggregateException aex) // 注意：AggregateException 为并行中专用的异常信息集合
	{
	Console.WriteLine($"Parallel.For has thrown an AggregateException. THIS WAS NOT EXPECTED.\n{aex}");
	//foreach (var item in aex.InnerExceptions) // 可以通过循环将全部信息记录下来
	//{
	// Console.WriteLine(item.InnerException.Message + " " + item.GetType().Name);
	//}
	//aex.Handle(p => // 如果想往上级抛，需要使用 Handle 方法处理一下
	//{
	// if (p.InnerException.Message == "my god！Exception from childTask1 happend！")
	// return true;
	// else
	// return false; // 返回 false 表示往上继续抛出异常
	//});
	}
	catch (OperationCanceledException ocex) // 专门用于取消循环异常的捕捉
	{
	Console.WriteLine($"An iteration has triggered a cancellation. THIS WAS EXPECTED.\n{ocex}");
	}
	finally
	{
	cancellationSource.Dispose();
	}
	}

	public static ParallelLoopResult For<TLocal> (int fromInclusive, int toExclusive,
	ParallelOptions parallelOptions,
	Func<TLocal> localInit,
	Func<int,ParallelLoopState,TLocal,TLocal> body,
	Action<TLocal> localFinally);

	static void Main(string[] args)
	{
	int result = 0;
	int N = 1000000;
	Parallel.For(
	0, N,
	// 限制最多 4 个并行任务
	new ParallelOptions { MaxDegreeOfParallelism = 4 },
	// Func<TLocal> 初始化本地变量，本地变量是线程独立变量
	() => 0,
	// Func<Int32,ParallelLoopState,TLocal,TLocal> 迭代操作
	(i, loop, localState) =>
	{
	for (int ii = 0; ii < 10000; ii++) ;
	return localState + 1;
	},
	localState =>
	Interlocked.Add(ref result, localState)
	);
	Console.WriteLine("实际运算结果： {0}. 目标值： 1000000", result);
	Console.ReadLine();
	}

	static void Main(string[] args)
	{
	int[] ints = { 11, 12, 13, 14, 15, 16, 17, 18, 19 };
	ParallelLoopResult result = Parallel.ForEach(ints,
	i =>
	{
	Console.WriteLine(i);
	});
	Console.ReadLine();
	}

	static void Main(string[] args)
	{
	// 创建一个集合，其中包含一些数字
	var numbers = new int[] { 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 };
	// 使用 ParallelOptions 选项设置并行处理的行为
	var parallelOptions = new ParallelOptions
	{
	MaxDegreeOfParallelism = 5
	};
	Parallel.ForEach(numbers, parallelOptions, (source, loopState, index) => // index：集合中对象的从 0 开始的序号
	{
	// 在此处编写并行处理逻辑
	Console.WriteLine($"开始--Index: {index}, Value: {source}, ThreadId: {Thread.GetCurrentProcessorId()}");
	if (loopState.ShouldExitCurrentIteration)
	return;
	Thread.Sleep(200);
	if (index == 6)
	loopState.Break();
	Console.WriteLine($"结束++Index: {index}, Value: {source}, ThreadId: {Thread.GetCurrentProcessorId()}");
	});
	Console.ReadLine();
	}

	long sum = 0;
	long sumtop = 10000000;
	Stopwatch sw = Stopwatch.StartNew();
	Parallel.ForEach(Partitioner.Create(0, sumtop), (range) =>
	{
	long local = 0;
	for (long i = range.Item1; i < range.Item2; i++)
	local += i;
	Interlocked.Add(ref sum, local); // Interlocked：为由多个线程共享的变量提供原子操作 Add()：求和后替换原来的数值，相当于 +=
	});
	sw.Stop();
	Console.WriteLine($"Partitioner.Create() 分区方式执行效率： result = {sum}, time = {sw.ElapsedMilliseconds} ms");
	// 输出：
	// Partitioner.Create() 分区方式执行效率： result = 49999995000000, time = 8 ms

	public static ParallelLoopResult ForEach<TSource,TLocal> (IEnumerable<TSource> source,
	Func<TLocal> localInit,
	Func<TSource,ParallelLoopState,TLocal,TLocal> body,
	Action<TLocal> localFinally);

	static void Main(string[] args)
	{
	// 全部值的和为 40
	int[] input = { 4, 1, 6, 2, 9, 5, 10, 3 };
	int sum = 0;
	try
	{
	Parallel.ForEach(
	// IEnumerable<TSource> 可枚举的数据源
	input,
	// Func<TLocal> 用于返回每个任务的【本地数据的初始状态】的函数委托
	// 本示例中的目的就是将 TLocal localSum 的值在每次迭代都赋值为 0
	() => 0,
	// Func<TSource,ParallelLoopState,TLocal,TLocal> 将为每个迭代调用一次的委托
	(n, loopState, localSum) =>
	{
	localSum += n;
	Console.WriteLine($"Thread={Thread.CurrentThread.ManagedThreadId}, n={n}, localSum={localSum}");
	return localSum;
	},
	// Action<TLocal> 用于对每个任务的本地状态执行一个最终操作的委托
	// 此示例中的作用是将每个值逐一求和，并返回 sum
	(localSum) =>
	Interlocked.Add(ref sum, localSum)
	);
	Console.WriteLine("\nSum={0}", sum);
	}
	catch (AggregateException e)
	{
	Console.WriteLine("Parallel.ForEach has thrown an exception. This was not expected.\n{0}", e);
	}
	Console.ReadLine();
	}

	static void Main(string[] args)
	{
	Stopwatch sw = null;
	long sum = 0;
	long sumtop = 10000000;
	// 常规 for 循环
	sw = Stopwatch.StartNew();
	for (long i = 0; i < sumtop; i++)
	sum += i;
	sw.Stop();
	Console.WriteLine($"result = {sum}, time = {sw.ElapsedMilliseconds} ms --常规 for 循环");

	// Parallel.For() 方式
	sum = 0;
	sw = Stopwatch.StartNew();
	Parallel.For(0L, sumtop,
	(item) => Interlocked.Add(ref sum, item));
	sw.Stop();
	Console.WriteLine($"result = {sum}, time = {sw.ElapsedMilliseconds} ms --Parallel.For() 方式");

	// Parallel.For() + TLocal
	sum = 0;
	sw = Stopwatch.StartNew();
	Parallel.For(
	0L, sumtop,
	() => 0L,
	(item, state, prevLocal) =>
	prevLocal + item,
	local =>
	Interlocked.Add(ref sum, local));
	sw.Stop();
	Console.WriteLine($"result = {sum}, time = {sw.ElapsedMilliseconds} ms --Parallel.For() + locals 方式");

	// Partitioner.Create() 分区方式
	sum = 0;
	sw = Stopwatch.StartNew();
	Parallel.ForEach(Partitioner.Create(0L, sumtop), (range) =>
	{
	long local = 0;
	for (long i = range.Item1; i < range.Item2; i++)
	local += i;
	Interlocked.Add(ref sum, local);
	});
	sw.Stop();
	Console.WriteLine($"result = {sum}, time = {sw.ElapsedMilliseconds} ms --Partitioner.Create() 分区方式");
	Console.ReadLine();
	}

	static async Task Main(string[] args)
	{
	var nums = Enumerable.Range(0, 10).ToArray();
	await Parallel.ForEachAsync(
	nums,
	new ParallelOptions { MaxDegreeOfParallelism = 3 }, // 配置最多同时分配三个线程
	async (i, token) => // Func<TSource,CancellationToken,ValueTask> // 其中 ValueTask 提供异步操作的可等待结果，指的是下文 await 的内容
	{
	Console.WriteLine($"开始迭代任务 {i} ThreadId:{Thread.GetCurrentProcessorId()}");
	// public static Task Delay(int millisecondsDelay, CancellationToken cancellationToken)
	// 在指定毫秒后，调用 token 取消当前任务
	await Task.Delay(1000, token);
	Console.WriteLine($"完成迭代任务 {i}");
	});
	Console.WriteLine("Finished!");
	Console.ReadLine();
	}

	static void Main(string[] args)
	{
	try
	{
	Parallel.Invoke(
	BasicAction, // 第一个操作 - 静态方法
	() => // 第二个操作 - 箭头函数
	{
	Console.WriteLine("Method=beta, Thread={0}", Thread.CurrentThread.ManagedThreadId);
	},
	delegate () // 第三个操作 - 委托函数
	{
	Console.WriteLine("Method=gamma, Thread={0}", Thread.CurrentThread.ManagedThreadId);
	}
	);
	}
	catch (AggregateException e)
	{
	Console.WriteLine("An action has thrown an exception. THIS WAS UNEXPECTED.\n{0}", e.InnerException.ToString());
	}
	Console.ReadLine();
	}
	static void BasicAction()
	{
	Console.WriteLine("Method=alpha, Thread={0}", Thread.CurrentThread.ManagedThreadId);
	}