C# 可指定并行度任务调度器

可指定并行度的任务调度器

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///

/// 指定最大并行度的任务调度器
///

public class SpecifyDegreeOfParallelismTaskScheduler : TaskScheduler
{
///

/// 信号量锁
///

private static System.Threading.SemaphoreSlim _lock = new System.Threading.SemaphoreSlim(1);

///

/// 当前线程是否正在处理任务
///

[ThreadStatic]
private static bool _currentThreadIsProcessingItems;

///

/// 执行的任务队列
///

private readonly LinkedList _tasks = new LinkedList();

///

/// 指定的最大并行度
///

private readonly int _maxDegressOfParallelism;

///

///当前调度器中正在执行的任务数
///

private int _runingTasks = 0;

///

/// 指示此调度器能够支持的最大并发级别。
///

public override int MaximumConcurrencyLevel { get { return this._maxDegressOfParallelism; } }

///

/// 初始化一个可指定最大并行度的任务调度器
///

/// 最大并行度
public SpecifyDegreeOfParallelismTaskScheduler(int maxDegreeOfParallelism)
{
if (maxDegreeOfParallelism < 1)
throw new ArgumentOutOfRangeException("maxDegreeOfParallelism至少为1");
this._maxDegressOfParallelism = maxDegreeOfParallelism;
}

///

/// 将Task排队到调度器中
///

/// 要排队的任务
protected override void QueueTask(Task task)
{
_lock.Wait();
try
{
this._tasks.AddLast(task);
if (this._runingTasks < this._maxDegressOfParallelism)
{
++this._runingTasks;
ConsumeTaskOfPending();
}
}
finally
{
_lock.Release();
}
}

///

/// 尝试在当前线程上执行指定的任务
///

/// 被执行的任务
/// 指定的任务之前是否已经排队
/// 是否能在当前线程执行此任务
protected override bool TryExecuteTaskInline(Task task, bool taskWasPreviouslyQueued)
{
//如果当前前程没有正在处理项目，无法内联
if (!_currentThreadIsProcessingItems)
return false;

//如果任务之前已经被排队，将其从队列中删除
if (taskWasPreviouslyQueued)
TryDequeue(task);
return base.TryExecuteTask(task);
}

///

/// 消费队列中等待的任务
///

private void ConsumeTaskOfPending()
{
ThreadPool.UnsafeQueueUserWorkItem(p =>
{
_currentThreadIsProcessingItems = true;
try
{
while (true)
{
Task item;
_lock.Wait();
try
{
if (this._tasks.Count == 0)
{
--this._runingTasks;
break;
}
item = this._tasks.First.Value;
this._tasks.RemoveFirst();
}
finally
{
_lock.Release();
}
base.TryExecuteTask(item);
}
}
finally
{
_currentThreadIsProcessingItems = false;
}
}, null);
}

///

/// 尝试将任务从队列移除
///

/// 要移除的任务
/// 是否成功将任务从队列中移除
protected override bool TryDequeue(Task task)
{
_lock.Wait();
try
{
return this._tasks.Remove(task);
}
finally
{
_lock.Release();
}
}

///

/// 获取当前调度器中已调度任务序列
///

/// 可遍历已调度任务序列
protected override IEnumerable GetScheduledTasks()
{
_lock.Wait();
try
{
return this._tasks.ToArray();
}
finally
{
_lock.Release();
}
}

}