QT虚拟内存数据共享

本例子利用虚拟内存实现不同进程或线程内的数据共享,不同进程中请勿使用信号槽update。

QSharedMemoryOper.h

#ifndef QSHAREDMEMORYOPER_H
#define QSHAREDMEMORYOPER_H

#include 
#include 
const static int nMemorySize = 1024 * 1024;
class QSharedMemoryOper : public QObject
{
    Q_OBJECT
public:
    QSharedMemoryOper(QObject *parent = nullptr);
    ~QSharedMemoryOper();

private:
    QSharedMemory m_shareMemory;

public:
    void SetKey(const QString &key);
    int ReadData(char *pBuffer, int nMaxLen);                   //返回实际长度
    int WriteData(char *pBuffer, int nLen, int nWritePos = -1); //写入全部数据

signals:
    void update(); //数据更新
};

#endif // QSHAREDMEMORYOPER_H

QSharedMemoryOper.cpp

#include "qsharedmemoryoper.h"

static QMap> sharedMemoryOperMap;
#pragma pack(push, 1) //按字节对齐begin

struct QSharedMemoryInfo
{
    int nFlashLen;      //代表有效数据大小
    char pFlashData[1]; //代表数据
};

#pragma pack(pop) //按字节对齐end

QSharedMemoryOper::QSharedMemoryOper(QObject *parent)
    : QObject(parent)
{}

QSharedMemoryOper::~QSharedMemoryOper()
{
    QList qList = sharedMemoryOperMap.value(m_shareMemory.key());
    qList.removeOne(this);
    sharedMemoryOperMap.insert(m_shareMemory.key(), qList);
    m_shareMemory.detach();
}

void QSharedMemoryOper::SetKey(const QString &key)
{
    if (key != "") {
        m_shareMemory.setKey(key);
        if (!m_shareMemory.create(nMemorySize + sizeof(int)))
            m_shareMemory.attach();
        QList qList = sharedMemoryOperMap.value(key);
        qList.append(this);
        sharedMemoryOperMap.insert(key, qList);
    }
}

int QSharedMemoryOper::ReadData(char *pBuffer, int nMaxLen)
{
    if (m_shareMemory.isAttached()) {
        m_shareMemory.lock();
        QSharedMemoryInfo *pSharedMemoryInfo = (QSharedMemoryInfo *) m_shareMemory.data();
        int nLen = nMaxLen >= pSharedMemoryInfo->nFlashLen ? pSharedMemoryInfo->nFlashLen : nMaxLen;
        memcpy(pBuffer, pSharedMemoryInfo->pFlashData, nLen);
        m_shareMemory.unlock();
        return nLen;
    }
    return -1;
}

int QSharedMemoryOper::WriteData(char *pBuffer, int nLen, int nWritePos)
{
    if (m_shareMemory.isAttached()
        && (nLen < nMemorySize - sizeof(int) || (nWritePos == -1 && nWritePos + nLen < nMemorySize - sizeof(int)))) {
        m_shareMemory.lock();
        QSharedMemoryInfo *pSharedMemoryInfo = (QSharedMemoryInfo *) m_shareMemory.data();
        int nFlashLen = pSharedMemoryInfo->nFlashLen;
        if (nWritePos == -1) {
            pSharedMemoryInfo->nFlashLen = nLen;
            nFlashLen = nLen;
            memcpy(pSharedMemoryInfo->pFlashData, pBuffer, nLen);
        } else {
            memcpy(pSharedMemoryInfo->pFlashData + nWritePos, pBuffer, nLen);
            return pSharedMemoryInfo->nFlashLen;
        }
        m_shareMemory.unlock();
        QList qList = sharedMemoryOperMap.value(m_shareMemory.key());
        for (int i = 0; i < qList.length(); i++) {
            if (qList.at(i) != this)
                emit qList.at(i)->update();
        }
        return nFlashLen;
    }
    return -1;
}