QSharedMemory共享内存Shared Memory是一种进程间通信Inter-Process Communication, IPC机制允许多个进程共享同一块内存区域。共享内存提供了高效的数据交换方式适用于需要频繁传递大量数据的场景。Qt中的共享内存机制主要依赖于QSharedMemory类。该类提供了用于创建和管理共享内存区域的接口允许进程在内存中创建一个共享的数据缓冲区.使用步骤创建共享内存使用QSharedMemory类的create()函数可以创建一个共享内存对象并指定一个唯一的键key来标识共享内存区域。如果该键对应的共享内存已经存在则会返回false。分配内存使用QSharedMemory类的attach()函数将共享内存附加到当前进程的地址空间。写入和读取数据通过共享内存附加到的地址进程可以直接读取或写入共享内存中的数据。可以使用任何数据结构如数组、结构体等来组织共享的数据。分离和删除共享内存当进程不再需要访问共享内存时可以使用QSharedMemory类的detach()函数将共享内存从当前进程的地址空间中分离。而使用QSharedMemory类的remove()函数可以删除共享内存区域释放相关资源。跨平台特性差异windows内核自动回收进程退出后内存自动释放linuxQSharedMemory 持有需显式调用析构函数示例写入端#includeQtCore/QCoreApplication#includeQSharedMemory#includeQDebug#includeQThread#includeqmath.hintmain(intargc,char*argv[]){QCoreApplicationa(argc,argv);QSharedMemory*shared_mmnewQSharedMemory();shared_mm-setKey(my_shared_data);if(!shared_mm-attach(QSharedMemory::ReadWrite)){shared_mm-create(20,QSharedMemory::ReadWrite);intno0;QString ret;while(true){no1;shared_mm-lock();retQString(shared no:%0).arg(no);memset(shared_mm-data(),0,shared_mm-size());memcpy(shared_mm-data(),ret.toStdString().data(),qMin(ret.size(),shared_mm-size()));shared_mm-unlock();QThread::sleep(2);qDebug()ret;}}else{qDebug()app1 attach my_shared_data failed!;}returna.exec();}读取端#includeQtCore/QCoreApplication#includeQSharedMemory#includeQDebug#includeQThread#includeqmath.hintmain(intargc,char*argv[]){QCoreApplicationa(argc,argv);QSharedMemory*shared_mmnewQSharedMemory();shared_mm-setKey(my_shared_data);if(!shared_mm-attach(QSharedMemory::ReadWrite)){shared_mm-create(20,QSharedMemory::ReadWrite);intno0;QString ret;while(true){no1;shared_mm-lock();retQString(shared no:%0).arg(no);memset(shared_mm-data(),0,shared_mm-size());memcpy(shared_mm-data(),ret.toStdString().data(),qMin(ret.size(),shared_mm-size()));shared_mm-unlock();QThread::sleep(2);qDebug()ret;}}else{qDebug()app1 attach my_shared_data failed!;}returna.exec();}如果是一个进程写多个进程读的场景可以考虑内存分页不同的进程读取不同的内存段# 示例代码constintPAGE_SIZE2048;// 内存页2kintapp_page2;memcpy(shared_mm-data()2*PAGE_SIZE,ret.toStdString().data(),qMin(ret.size(),shared_mm-size()));QSystemSemaphore如果两端都需要写入需要借助系统信号来控制读、写的时机信号量为0时会阻塞线程或进程。app1初始化‘sys_shared_semaphore1’、‘sys_shared_semaphore2’两个信号量同时启动时初始化‘my_shared_data’共享存储区。app1向共享存储区写入数据设置sys_shared_semaphore1的信号量为1然后等待sys_shared_semaphore2获取到信号量后读取数据。#includeQtCore/QCoreApplication#includeQSharedMemory#includeQDebug#includeQThread#includeQMath.h#includeQSystemSemaphoreintmain(intargc,char*argv[]){QCoreApplicationa(argc,argv);QSystemSemaphoresemaphore1(sys_shared_semaphore1,0);QSystemSemaphoresemaphore2(sys_shared_semaphore2,0);QSharedMemory*shared_mmnewQSharedMemory();shared_mm-setKey(my_shared_data);charbuff[20]{0};if(!shared_mm-attach(QSharedMemory::ReadWrite)){shared_mm-create(20,QSharedMemory::ReadWrite);intno0;QString ret;while(true){no1;shared_mm-lock();retQString(app1 no:%0).arg(no);memset(shared_mm-data(),0,shared_mm-size());memcpy(shared_mm-data(),ret.toStdString().data(),qMin(ret.size(),shared_mm-size()));shared_mm-unlock();semaphore1.release(1);if(semaphore2.acquire()){memset(buff,0,20);shared_mm-lock();memcpy(buff,shared_mm-constData(),sizeof(buff));qDebug()read sharememory:buff;shared_mm-unlock();}}}else{qDebug()app1 attach my_shared_data failed!;}returna.exec();}app2与app1差不多启动后先附加‘my_shared_data’附加成功表示app1已经启动然后等待sys_shared_semaphore1信号获取信号后读取数据。app2向共享存储区写入数据后设置sys_shared_semaphore2的信号量为1此时app1获取信号后可以读取数据。#includeQtCore/QCoreApplication#includeQSharedMemory#includeQDebug#includeQThread#includeQMath.h#includeQSystemSemaphoreintmain(intargc,char*argv[]){QCoreApplicationa(argc,argv);QSystemSemaphoresemaphore1(sys_shared_semaphore1,0);QSystemSemaphoresemaphore2(sys_shared_semaphore2,0);QSharedMemory*shared_mmnewQSharedMemory();shared_mm-setKey(my_shared_data);while(true){if(shared_mm-attach(QSharedMemory::ReadWrite))break;QThread::msleep(1000);qDebug()wait sharememory attach...;}intno0;QString ret;charbuff[20]{0};while(true){no1;if(semaphore1.acquire()){memset(buff,0,20);shared_mm-lock();memcpy(buff,shared_mm-constData(),sizeof(buff));qDebug()read sharememory:buff;shared_mm-unlock();}shared_mm-lock();retQString(app2 no:%0).arg(no);memset(shared_mm-data(),0,shared_mm-size());memcpy(shared_mm-data(),ret.toStdString().data(),qMin(ret.size(),shared_mm-size()));shared_mm-unlock();semaphore2.release(1);}returna.exec();}QtROQt Remote Object (QtRO)也是一个用于进程间通信IPC的模块专门用于在不同进程或计算机之间交换信息。它在Qt 5.9之后推出基于Socket封装兼容LPCLocal Process Communication和RPCRemote Process Communication。为了实现远程对象调用QtRO使用了一种基于信号和槽的机制类似于Qt本地对象之间的通信。qt工程中QtRO依赖 network、remoteobjects两个模块rep文件rep文件中包含了通信之间定义的接口。// 文件名app_rep_intf.rep class AppRemoteInterface { SIGNAL(signalMsg(const QString )) //server下发消息给client SLOT(int onMsg(const QString )) //server接收client的消息 }serverrep_app_rep_intf_source.h 是app_rep_intf.rep生成的.pro文件中需要添加REPC_SOURCE $$PWD/app_rep_intf.repvs 工程中需要设置app_rep_intf.rep属性out file typesource (Source header)#pragma once #include QDebug #include rep_app_rep_intf_source.h class AppRemoteInterface :public AppRemoteInterfaceSource { Q_OBJECT public: AppRemoteInterface(QObject *parent nullptr) : AppRemoteInterfaceSource() { } virtual int onMsg(const QString msg); void sendMsgToClient(const QString msg); signals: void signalRevMsg(const QString msg); }; #include appremoteinterface.h int AppRemoteInterface::onMsg(const QString msg) { emit signalRevMsg(msg); return 0; } void AppRemoteInterface::sendMsgToClient(const QString msg) { emit signalMsg(msg); }main.cpp#include QtCore/QCoreApplication #include QRemoteObjectHost #include QDebug #include QTimer #include appremoteinterface.h int main(int argc, char *argv[]) { QCoreApplication a(argc, argv); QRemoteObjectHost app_host; app_host.setHostUrl(QUrl(local:apprmt)); AppRemoteInterface *app_int new AppRemoteInterface(); app_host.enableRemoting(app_int); qDebug() server app running....; QObject::connect(app_int, AppRemoteInterface::signalRevMsg, [](const QString msg) { qDebug() server recv: msg; }); QTimer timer; QObject::connect(timer, QTimer::timeout, [app_int]() { app_int-sendMsgToClient(this is server msg!); }); timer.start(3000); return a.exec(); }clientrep_app_rep_intf_replica.h 是app_rep_intf.rep生成的.pro文件中需要添加REPC_REPLICA app_rep_intf.repvs 工程中需要设置app_rep_intf.rep属性out file typereplica (Replica header)#includeQtCore/QCoreApplication#includeQRemoteObjectHost#includeQDebug#includeQTimer#includeQMetaObject#includerep_app_rep_intf_replica.hintmain(intargc,char*argv[]){QCoreApplicationa(argc,argv);QRemoteObjectNode app_node;AppRemoteInterfaceReplica*app_infapp_node.acquireAppRemoteInterfaceReplica();app_node.connectToNode(QUrl(local:apprmt));QObject::connect(app_inf,AppRemoteInterfaceReplica::signalMsg,[](constQStringmsg){qDebug()client recv:msg;});QTimer timer;QObject::connect(timer,QTimer::timeout,[app_inf](){if(app_inf-isReplicaValid()){app_inf-onMsg(this is client msg);// 直接调用服务端的SOLT}});timer.start(3000);returna.exec();}