issue the i/o if not overlapped, and block until i/o complete.-优快云博客

本文链接：https://blog.youkuaiyun.com/Y12231819/article/details/128669916

CAsyncRequest类代表单个待处理的请求，其I/O操作在Complete方法中执行。初始化请求参数后，调用Complete方法进行文件读取操作，处理可能的错误和数据不匹配情况。CAsyncIo类用于管理多个异步请求，维护工作列表和已完成列表。

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//------------------------------------------------------------------------------
// File: AsyncIo.cpp
//
// Desc: DirectShow sample code - base library with I/O functionality.
//
// Copyright (c) Microsoft Corporation. All rights reserved.
//------------------------------------------------------------------------------

#include "stdafx.h"
#include <streams.h>
#include "asyncio.h"

// --- CAsyncRequest ---

// implementation of CAsyncRequest representing a single
// outstanding request. All the i/o for this object is done
// in the Complete method.

// init the params for this request.
// Read is not issued until the complete call
HRESULT
CAsyncRequest::Request(
CAsyncIo *pIo,
CAsyncStream *pStream,
LONGLONG llPos,
LONG lLength,
BOOL bAligned,
BYTE* pBuffer,
LPVOID pContext, // filter's context
DWORD dwUser) // downstream filter's context
{
m_pIo = pIo;
m_pStream = pStream;
m_llPos = llPos;
m_lLength = lLength;
m_bAligned = bAligned;
m_pBuffer = pBuffer;
m_pContext = pContext;
m_dwUser = dwUser;
m_hr = VFW_E_TIMEOUT; // not done yet

return S_OK;
}

// issue the i/o if not overlapped, and block until i/o complete.
// returns error code of file i/o
//
//
HRESULT
CAsyncRequest::Complete()
{
m_pStream->Lock();

m_hr = m_pStream->SetPointer(m_llPos);
if(S_OK == m_hr)
{
DWORD dwActual;

m_hr = m_pStream->Read(m_pBuffer, m_lLength, m_bAligned, &dwActual);
if(m_hr == OLE_S_FIRST)
{
if(m_pContext)
{
IMediaSample *pSample = reinterpret_cast<IMediaSample *>(m_pContext);
pSample->SetDiscontinuity(TRUE);
m_hr = S_OK;
}
}

if(FAILED(m_hr))
{
}
else if(dwActual != (DWORD)m_lLength)
{
// tell caller size changed - probably because of EOF
m_lLength = (LONG) dwActual;
m_hr = S_FALSE;
}
else
{
m_hr = S_OK;
}
}

m_pStream->Unlock();
return m_hr;
}

// --- CAsyncIo ---

// note - all events created manual reset

CAsyncIo::CAsyncIo(CAsyncStream *pStream)
: m_hThread(NULL),
m_evWork(TRUE),
m_evDone(TRUE),
m_evStop(TRUE),
m_listWork(NAME("Work list")),
m_listDone(NAME("Done list")),
m_bFlushing(FALSE),
m_cItemsOut(0),
m_bWaiting(FALSE),
m_pStream(pStream)
{