内核对象之异步IO请求完成时调用一个函数

步骤：

　　1、创建一个

void CALLBACK OverlappedRountine(
 PTP_CALLBACK_INSTANCE pInstance,
 PVOID pvContext,
 PVOID pOverlapped,
 ULONG IoResult,
 ULONG_PTR NumberOfBytesTransferred,
 PTP_IO pIo)

类似的函数

　　2、打开一个文件

　　3、CreateThreadpoolIo，创建一个IO线程池

　　4、在调用异步操作前都调用一下StartThreadpoolIo这个函数

　　5、WaitForThreadpoolIoCallbacks(pIo, FALSE);表示等待到所有操作结束。如果为TRUE，则是将未完成的操作结束，并返回。

个人理解：

　　1、将IO完成后，返回后到的线程指定了，而且是每一个异步操作都会进入到此函数。

　　2、因为此线程池在内部采用了IO完成端口的方式，所以我们的操作会是顺序，因为在IO完成端口里面维护着一个队列

代码：

#include <iostream>
#include <afx.h>
#include <stdio.h>
using namespace std;

byte buf[1000];

void OutPut(byte buffer[], int num)
{
	cout << "数据为：";
	if(num > 0)
	{
		for (int i = 0; i < num; i++)
		{
			printf("%02X  ", buffer[i]);
		}
		cout << endl;
	}
	else cout << " 空 " << endl;

}

void CALLBACK OverlappedRountine(
	PTP_CALLBACK_INSTANCE pInstance,
	PVOID pvContext,
	PVOID pOverlapped,
	ULONG IoResult,
	ULONG_PTR NumberOfBytesTransferred,
	PTP_IO pIo)
{
	cout << "线程ID：" << GetCurrentThreadId() << endl;
	OVERLAPPED overLap = *((OVERLAPPED*)pOverlapped);
	OutPut(buf, NumberOfBytesTransferred);
	Sleep(2000);
} 

void InitCOM(HANDLE &hCOM)
{
	SetupComm(hCOM, 1024, 512); 
	PurgeComm(hCOM, PURGE_RXABORT | PURGE_RXCLEAR | PURGE_TXABORT | PURGE_TXCLEAR); 


	COMMTIMEOUTS CommTimeout; 
	CommTimeout.ReadIntervalTimeout = 5; 
	CommTimeout.ReadTotalTimeoutConstant = 1000; 
	CommTimeout.ReadTotalTimeoutMultiplier = 5; 
	CommTimeout.WriteTotalTimeoutConstant = 1000; 
	CommTimeout.WriteTotalTimeoutMultiplier = 5; 

	SetCommTimeouts(hCOM, &CommTimeout); 

	DCB dcb; 
	GetCommState(hCOM, &dcb); 
	dcb.BaudRate = 4800; 
	dcb.ByteSize = 8; 
	dcb.Parity = NOPARITY; 
	dcb.StopBits = ONESTOPBIT; 
	dcb.fBinary = TRUE; 
	dcb.fParity = FALSE; 

	SetCommState(hCOM, &dcb); 
}



void main()
{
	HANDLE hCOM = CreateFile(L"COM3", GENERIC_WRITE | GENERIC_READ, 0
		, NULL, OPEN_EXISTING, FILE_FLAG_OVERLAPPED, NULL);
	cout << "打开COM的返回代码：" << GetLastError() << endl;
	PTP_IO pIo = CreateThreadpoolIo(hCOM, OverlappedRountine, NULL, NULL);
	cout << "创建线程池的返回代码：" << GetLastError() << endl;

	InitCOM(hCOM);

	StartThreadpoolIo(pIo);
	byte data = 0x1a;
	DWORD dwLen = 0;

	OVERLAPPED overLap;
	overLap.hEvent = 0;
	overLap.Offset = 0;
	overLap.OffsetHigh = 0;

	WriteFile(hCOM, &data, sizeof(data), &dwLen, &overLap);

	OVERLAPPED overLap2;
	overLap2.hEvent = 0;
	overLap2.Offset = 0;
	overLap2.OffsetHigh = 0;
	
	for (int i = 0; i < 10; ++i)
	{
		StartThreadpoolIo(pIo);
		ReadFile(hCOM, buf, 1000, &dwLen, &overLap2);
	}

	WaitForThreadpoolIoCallbacks(pIo, FALSE);
	
	CloseHandle(hCOM);
	CloseThreadpoolIo(pIo);
}

 结果：

　　

结果分析：

　　我们可以发现，此时更加能够体现线程池的特点。2个线程，相互交替工作。