c# Parallel类的使用

static void ParallelFor()
{
  ParallelLoopResult result =
    Parallel.For(0, 10, async i =>
      {
        Console.WriteLine("{0}, task: {1}, thread: {2}", i,
          Task.CurrentId, Thread.CurrentThread.ManagedThreadId);

        await Task.Delay(10);//异步方法，用于释放线程供其他任务使用。完成后，可能看不到方法的输出，因为主(前台线)程结束，所有的后台线程也将结束
        Console.WriteLine("{0}, task: {1}, thread: {2}", i, Task.CurrentId, Thread.CurrentThread.ManagedThreadId);
      });
  Console.WriteLine("Is completed: {0}", result.IsCompleted);
}

static void ParallelFor()
{
  ParallelLoopResult result = Parallel.For(10, 40, (int i, ParallelLoopState pls) =>
     {
       Console.WriteLine("i: {0} task {1}", i, Task.CurrentId);
       Thread.Sleep(10);
       if (i > 15)
         pls.Break();
     });
  Console.WriteLine("Is completed: {0}", result.IsCompleted);
  if (!result.IsCompleted)
    Console.WriteLine("lowest break iteration: {0}", result.LowestBreakIteration);
}

static void ParallelFor()
{
  Parallel.For<string>(0, 20, () =>
   {
     // invoked once for each thread
     Console.WriteLine("init thread {0}, task {1}", Thread.CurrentThread.ManagedThreadId, Task.CurrentId);
     return String.Format("t{0}", Thread.CurrentThread.ManagedThreadId);
   },
   (i, pls, str1) =>
   {
     // invoked for each member
     Console.WriteLine("body i {0} str1 {1} thread {2} task {3}", i, str1, Thread.CurrentThread.ManagedThreadId, Task.CurrentId);
     Thread.Sleep(10);
     return String.Format("i {0}", i);
   },
   (str1) =>
   {
     // final action on each thread
     Console.WriteLine("finally {0}", str1);
   });
}

static void ParallelForeach()
{
  string[] data = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", "eleven", "twelve" };

  ParallelLoopResult result = Parallel.ForEach<string>(data, s =>
       {
         Console.WriteLine(s);
       });
  Parallel.ForEach<string>(data, (s, pls, l) =>
  {
    Console.WriteLine("{0} {1}", s, l);
  });
}

static void ParallelInvoke()
{
  Parallel.Invoke(Foo, Bar);
}

static void Foo()
{
  Console.WriteLine("foo");
}

static void Bar()
{
  Console.WriteLine("bar");
}

static void CancelParallelLoop()
{
  var cts = new CancellationTokenSource();
  cts.Token.ThrowIfCancellationRequested();
  cts.Token.Register(() => Console.WriteLine("** token cancelled"));
  // 在500ms后取消标记
  cts.CancelAfter(500);
  try
  {
    ParallelLoopResult result = Parallel.For(0, 100,
      new ParallelOptions()
      {
        CancellationToken = cts.Token
      },
        x =>
        {
          Console.WriteLine("loop {0} started", x);
          int sum = 0;
          for (int i = 0; i < 100; i++)
          {
            Thread.Sleep(2);
            sum += i;
          }
          Console.WriteLine("loop {0} finished", x);
        });
  }
  catch (OperationCanceledException ex)
  {
    Console.WriteLine(ex.Message);
  }
}

/*   示例1  */public static void PartitionerTest()
{
  //使用计时器
  System.Diagnostics.Stopwatch stopwatch = new System.Diagnostics.Stopwatch();
  const int maxValue = 1000000000;
  long sum = 0;
  stopwatch.Restart();//开始计时
  Parallel.For(0, maxValue, (i) => {
    Interlocked.Add(ref sum, (long )Math.Sqrt(i));//Interlocked是原子操作，多线程访问时的线程互斥操作
  });
  stopwatch.Stop();
  Console.WriteLine($"Parallel.For:{stopwatch.Elapsed}");//我的机器运行出的时间是：00:01:37.0391204


  var partitioner = System.Collections.Concurrent.Partitioner.Create(0, maxValue);//拆分区间
  sum = 0;
  stopwatch.Restart();
  Parallel.ForEach(partitioner, (rang) => {
    long partialSum = 0;
    //迭代区间的数据
    for(int i=rang.Item1;i<rang.Item2;i++)
    {
      partialSum += (long)Math.Sqrt(i);
    }
    Interlocked.Add(ref sum, partialSum);//原子操作
  });
  stopwatch.Stop();
  Console.WriteLine($"Parallel.ForEach:{stopwatch.Elapsed}"); //我的机器运行出的时间是：00:00:02.7111666
}

//声明一个委托
 private delegate int MathOp(int x, int y);
 private int Add(int x,int y)
 {
   return x + y;
 }

 private int DoOperation(MathOp op,int x,int y)
 {
   return op(x, y);
 }

 /*
 * 委托会设计两类开销：构造开销和调用开销。大多数调用开销和普通方法的调用差不多。 但委托是一种对象，构造开销可能相当大，最好是只做一次构造，然后把对象缓存起来。
 */
 public void Test()
 {
   System.Diagnostics.Stopwatch stopwatch = new System.Diagnostics.Stopwatch();
   stopwatch.Restart();
   for(int i=0;i<10;i++)
   {
     //每一次遍历循环，都会产生一次构造和调用开销
     DoOperation(Add, 1, 2);
   }
   stopwatch.Stop();
   Console.WriteLine("Construction and invocation: {0}", stopwatch.Elapsed);//00:00:00.0003812

   stopwatch.Restart();
   MathOp op = Add;//只产生一次构造开销
   for(int i=0;i<10;i++)
   {
     DoOperation(op, 1, 2);//每一次遍历都只产生遍历开销
   }
   stopwatch.Stop();
   Console.WriteLine("Once Construction and invocation: {0}", stopwatch.Elapsed);//00:00:00.0000011
 }