阅读后this article其中指出:

After a device finishes its job , (IO operation)- it notifies the CPU via interrupt.

... ... ...

However, that “completion” status only exists at the OS level; the process has its own memory space that must be notified

... ... ...

Since the library/BCL is using the standard P/Invoke overlapped I/O system, it has already registered the handle with the I/O Completion Port (IOCP), which is part of the thread pool.

... ... ...

So an I/O thread pool thread is borrowed briefly to execute the APC, which notifies the task that it’s complete.

for (int i=0;i<1000;i++)
    {
      PingAsync_NOT_AWAITED(i); //notice not awaited !
    }

最佳答案

Does it mean that it grabs a new thread pool thread for each completed IO operation ? Or is it a dedicated number of threads for this ?

Does it mean that I'll have 1000 IOCP threadpool thread simultaneously ( sort of) running here , when all are finished ?

static void Main(string[] args) {
    printThreadCounts();
    var buffer = new byte[1024];
    const int requestCount = 30;
    int pendingRequestCount = requestCount;
    for (int i = 0; i != requestCount; ++i) {
        var stream = new FileStream(
            @"C:\Windows\win.ini",
            FileMode.Open, FileAccess.Read, FileShare.ReadWrite, 
            buffer.Length, FileOptions.Asynchronous
        );
        stream.BeginRead(
            buffer, 0, buffer.Length,
            delegate {
                Interlocked.Decrement(ref pendingRequestCount);
                Thread.Sleep(Timeout.Infinite);
            }, null
        );
    }
    do {
        printThreadCounts();
        Thread.Sleep(1000);
    } while (Thread.VolatileRead(ref pendingRequestCount) != 0);
    Console.WriteLine(new String('=', 40));
    printThreadCounts();
}

private static void printThreadCounts() {
    int completionPortThreads, maxCompletionPortThreads;
    int workerThreads, maxWorkerThreads;
    ThreadPool.GetMaxThreads(out maxWorkerThreads, out maxCompletionPortThreads);
    ThreadPool.GetAvailableThreads(out workerThreads, out completionPortThreads);
    Console.WriteLine(
        "Worker threads: {0}, Completion port threads: {1}, Total threads: {2}", 
        maxWorkerThreads - workerThreads, 
        maxCompletionPortThreads - completionPortThreads, 
        Process.GetCurrentProcess().Threads.Count
    );
}

Worker threads: 0, Completion port threads: 0, Total threads: 3
Worker threads: 0, Completion port threads: 8, Total threads: 12
Worker threads: 0, Completion port threads: 9, Total threads: 13
Worker threads: 0, Completion port threads: 11, Total threads: 15
Worker threads: 0, Completion port threads: 13, Total threads: 17
Worker threads: 0, Completion port threads: 15, Total threads: 19
Worker threads: 0, Completion port threads: 17, Total threads: 21
Worker threads: 0, Completion port threads: 19, Total threads: 23
Worker threads: 0, Completion port threads: 21, Total threads: 25
Worker threads: 0, Completion port threads: 23, Total threads: 27
Worker threads: 0, Completion port threads: 25, Total threads: 29
Worker threads: 0, Completion port threads: 27, Total threads: 31
Worker threads: 0, Completion port threads: 29, Total threads: 33
========================================
Worker threads: 0, Completion port threads: 30, Total threads: 34

stream.BeginRead(
    buffer, 0, buffer.Length,
    ar => {
        stream.EndRead(ar);
        Interlocked.Decrement(ref pendingRequestCount);
    }, null
);

Worker threads: 0, Completion port threads: 0, Total threads: 3
Worker threads: 0, Completion port threads: 1, Total threads: 11
========================================
Worker threads: 0, Completion port threads: 0, Total threads: 11

Worker threads: 0, Completion port threads: 0, Total threads: 3
Worker threads: 8, Completion port threads: 0, Total threads: 15
Worker threads: 9, Completion port threads: 0, Total threads: 16
Worker threads: 10, Completion port threads: 0, Total threads: 17
Worker threads: 11, Completion port threads: 0, Total threads: 18
Worker threads: 12, Completion port threads: 0, Total threads: 19
Worker threads: 13, Completion port threads: 0, Total threads: 20
Worker threads: 14, Completion port threads: 0, Total threads: 21
Worker threads: 15, Completion port threads: 0, Total threads: 22
Worker threads: 16, Completion port threads: 0, Total threads: 23
Worker threads: 17, Completion port threads: 0, Total threads: 24
Worker threads: 18, Completion port threads: 0, Total threads: 25
Worker threads: 19, Completion port threads: 0, Total threads: 26
Worker threads: 20, Completion port threads: 0, Total threads: 27
Worker threads: 21, Completion port threads: 0, Total threads: 28
Worker threads: 22, Completion port threads: 0, Total threads: 29
Worker threads: 23, Completion port threads: 0, Total threads: 30
Worker threads: 24, Completion port threads: 0, Total threads: 31
Worker threads: 25, Completion port threads: 0, Total threads: 32
Worker threads: 26, Completion port threads: 0, Total threads: 33
Worker threads: 27, Completion port threads: 0, Total threads: 34
Worker threads: 28, Completion port threads: 0, Total threads: 35
Worker threads: 29, Completion port threads: 0, Total threads: 36
========================================
Worker threads: 30, Completion port threads: 0, Total threads: 37

Worker threads: 0, Completion port threads: 0, Total threads: 3
Worker threads: 0, Completion port threads: 31, Total threads: 35
========================================
Worker threads: 0, Completion port threads: 30, Total threads: 35

关于c# - IOCP 线程 - 澄清？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/28690815/