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According to MSDN , async 和 await 不创建新线程:
The
asyncandawaitkeywords don't cause additional threads to be created.
考虑到这一点，我很难理解一些简单程序的控制流程。我的完整示例如下。请注意，它需要 Dataflow library ，您可以从 NuGet 安装它。
using System;
using System.Threading.Tasks.Dataflow;
namespace TaskSandbox
{
class Program
{
static void Main(string[] args)
{
BufferBlock<int> bufferBlock = new BufferBlock<int>();
Consume(bufferBlock);
Produce(bufferBlock);
Console.ReadLine();
}
static bool touched;
static void Produce(ITargetBlock<int> target)
{
for (int i = 0; i < 5; i++)
{
Console.Error.WriteLine("Producing " + i);
target.Post(i);
Console.Error.WriteLine("Performing intensive computation");
touched = false;
for (int j = 0; j < 100000000; j++)
;
Console.Error.WriteLine("Finished intensive computation. Touched: " + touched);
}
target.Complete();
}
static async void Consume(ISourceBlock<int> source)
{
while (await source.OutputAvailableAsync())
{
touched = true;
int received = source.Receive();
Console.Error.WriteLine("Received " + received);
}
}
}
}
输出:
Producing 0
Performing intensive computation
Received 0
Finished intensive computation. Touched: True
Producing 1
Performing intensive computation
Received 1
Finished intensive computation. Touched: True
Producing 2
Performing intensive computation
Received 2
Finished intensive computation. Touched: False
Producing 3
Performing intensive computation
Received 3
Finished intensive computation. Touched: False
Producing 4
Performing intensive computation
Received 4
Finished intensive computation. Touched: True
这似乎表明 Consume 在 for 循环运行时获得控制权，因为 OutputAvailableAsync 任务完成:
for (int j = 0; j < 100000000; j++)
;
这在线程模型中不足为奇。但是，如果不涉及额外的线程，Produce 如何在 for 循环中间产生控制权？