c# - IAsyncResult 的属性isCompleted 是如何更新的？

Question

当我异步调用一个方法时(使用模式 BeginXxx/EndXxx)，我在调用 BeginXxx 后得到一个 IAsyncResult 结果。如果方法 BeginXxxx 或 EndXxx 均未引用结果变量，属性“isCompleted”(在返回的结果变量中)如何更新？

例如:

// Create the delegate.
AsyncMethodCaller caller = new AsyncMethodCaller(ad.TestMethod);

// Initiate the asychronous call.
IAsyncResult result = caller.BeginInvoke(3000, out threadId, null, null);

// Poll while simulating work.
while(result.IsCompleted == false) {
    Thread.Sleep(250);
    Console.Write(".");
}

Answer 1

BeginInvoke 向您返回 IAsyncResult，因此它将具有对它的引用。这将在内部创建并发回给您。

例如FileStream中的BeginRead创建FileStreamAsyncResult然后返回:

private unsafe FileStreamAsyncResult BeginReadCore(byte[] bytes, int offset, int numBytes, AsyncCallback userCallback, object stateObject, int numBufferedBytesRead)
{
    NativeOverlapped* overlappedPtr;
    FileStreamAsyncResult ar = new FileStreamAsyncResult {
        _handle = this._handle,
        _userCallback = userCallback,
        _userStateObject = stateObject,
        _isWrite = false,
        _numBufferedBytes = numBufferedBytesRead
    };
    ManualResetEvent event2 = new ManualResetEvent(false);
    ar._waitHandle = event2;

    .....

    if (hr == 0x6d)
    {
        overlappedPtr->InternalLow = IntPtr.Zero;
        ar.CallUserCallback();
        return ar;
    }