QThread庫(kù)是QT中提供的跨平臺(tái)多線程實(shí)現(xiàn)方案,使用時(shí)需要繼承QThread這個(gè)基類,并重寫實(shí)現(xiàn)內(nèi)部的Run方法,由于該庫(kù)是基本庫(kù),默認(rèn)依賴于QtCore.dll這個(gè)基礎(chǔ)模塊,在使用時(shí)無(wú)需引入其他模塊.
實(shí)現(xiàn)簡(jiǎn)單多線程
QThread庫(kù)提供了跨平臺(tái)的多線程管理方案,通常一個(gè)QThread對(duì)象管理一個(gè)線程,在使用是需要從QThread類繼承并重寫內(nèi)部的Run方法,并在Run方法內(nèi)部實(shí)現(xiàn)多線程代碼.
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#include <QCoreApplication>#include <iostream>#include <QThread>class MyThread: public QThread{protected: volatile bool m_to_stop;protected: // 線程函數(shù)必須使用Run作為開(kāi)始 void run() { for(int x=0; !m_to_stop && (x <10); x++) { msleep(1000); std::cout << objectName().toStdString() << std::endl; } }public: MyThread() { m_to_stop = false; } // 用于設(shè)置結(jié)束符號(hào)為真 void stop() { m_to_stop = true; } // 輸出線程運(yùn)行狀態(tài) void is_run() { std::cout << "Thread Running = " << isRunning() << std::endl; } // 輸出線程完成狀態(tài)(是否結(jié)束) void is_finish() { std::cout << "Thread Finished = " << isFinished() << std::endl; }};int main(int argc, char *argv[]){ QCoreApplication a(argc, argv); // 定義線程數(shù)組 MyThread thread[10]; // 設(shè)置線程對(duì)象名字 for(int x=0;x<10;x++) { thread[x].setObjectName(QString("thread => %1").arg(x)); } // 批量調(diào)用run執(zhí)行 for(int x=0;x<10;x++) { thread[x].start(); thread[x].is_run(); thread[x].isFinished(); } // 批量調(diào)用stop關(guān)閉 for(int x=0;x<10;x++) { thread[x].wait(); thread[x].stop(); thread[x].is_run(); thread[x].is_finish(); } return a.exec();} |
向線程中傳遞參數(shù)
線程在執(zhí)行前可以通過(guò)調(diào)用MyThread中的自定義函數(shù),并在函數(shù)內(nèi)實(shí)現(xiàn)參數(shù)賦值,實(shí)現(xiàn)線程傳參操作.
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#include <QCoreApplication>#include <iostream>#include <QThread>class MyThread: public QThread{protected: int m_begin; int m_end; int m_result; void run() { m_result = m_begin + m_end; }public: MyThread() { m_begin = 0; m_end = 0; m_result = 0; } // 設(shè)置參數(shù)給當(dāng)前線程 void set_value(int x,int y) { m_begin = x; m_end = y; } // 獲取當(dāng)前線程名 void get_object_name() { std::cout << "this thread name => " << objectName().toStdString() << std::endl; } // 獲取線程返回結(jié)果 int result() { return m_result; }};int main(int argc, char *argv[]){ QCoreApplication a(argc, argv); MyThread thread[3]; // 分別將不同的參數(shù)傳入到線程函數(shù)內(nèi) for(int x=0; x<3; x++) { thread[x].set_value(1,2); thread[x].setObjectName(QString("thread -> %1").arg(x)); thread[x].start(); } // 等待所有線程執(zhí)行結(jié)束 for(int x=0; x<3; x++) { thread[x].get_object_name(); thread[x].wait(); } // 獲取線程返回值并相加 int result = thread[0].result() + thread[1].result() + thread[2].result(); std::cout << "sum => " << result << std::endl; return a.exec();} |
QMutex 互斥同步線程鎖
QMutex類是基于互斥量的線程同步鎖,該鎖lock()鎖定與unlock()解鎖必須配對(duì)使用,線程鎖保證線程間的互斥,利用線程鎖能夠保證臨界資源的安全性.
- 線程鎖解決的問(wèn)題: 多個(gè)線程同時(shí)操作同一個(gè)全局變量,為了防止資源的無(wú)序覆蓋現(xiàn)象,從而需要增加鎖,來(lái)實(shí)現(xiàn)多線程搶占資源時(shí)可以有序執(zhí)行.
- 臨界資源(Critical Resource): 每次只允許一個(gè)線程進(jìn)行訪問(wèn) (讀/寫)的資源.
- 線程間的互斥(競(jìng)爭(zhēng)): 多個(gè)線程在同一時(shí)刻都需要訪問(wèn)臨界資源.
- 一般性原則: 每一個(gè)臨界資源都需要一個(gè)線程鎖進(jìn)行保護(hù).
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#include <QCoreApplication>#include <iostream>#include <QThread>#include <QMutex>static QMutex g_mutex; // 線程鎖static QString g_store; // 定義全局變量class Producer : public QThread{protected: void run() { int count = 0; while(true) { // 加鎖 g_mutex.lock(); g_store.append(QString::number((count++) % 10)); std::cout << "Producer -> "<< g_store.toStdString() << std::endl; // 釋放鎖 g_mutex.unlock(); msleep(900); } }};class Customer : public QThread{protected: void run() { while( true ) { g_mutex.lock(); if( g_store != "" ) { g_store.remove(0, 1); std::cout << "Curstomer -> "<< g_store.toStdString() << std::endl; } g_mutex.unlock(); msleep(1000); } }};int main(int argc, char *argv[]){ QCoreApplication a(argc, argv); Producer p; Customer c; p.setObjectName("producer"); c.setObjectName("curstomer"); p.start(); c.start(); return a.exec();} |
QMutexLocker是在QMutex基礎(chǔ)上簡(jiǎn)化版的線程鎖,QMutexLocker會(huì)保護(hù)加鎖區(qū)域,并自動(dòng)實(shí)現(xiàn)互斥量的鎖定和解鎖操作,可以將其理解為是智能版的QMutex鎖,該鎖只需要在上方代碼中稍加修改即可.
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#include <QMutex>#include <QMutexLocker>static QMutex g_mutex; // 線程鎖static QString g_store; // 定義全局變量class Producer : public QThread{protected: void run() { int count = 0; while(true) { // 增加智能線程鎖 QMutexLocker Locker(&g_mutex); g_store.append(QString::number((count++) % 10)); std::cout << "Producer -> "<< g_store.toStdString() << std::endl; msleep(900); } }}; |
互斥鎖存在一個(gè)問(wèn)題,每次只能有一個(gè)線程獲得互斥量的權(quán)限,如果在程序中有多個(gè)線程來(lái)同時(shí)讀取某個(gè)變量,那么使用互斥量必須排隊(duì),效率上會(huì)大打折扣,基于QReadWriteLock讀寫模式進(jìn)行代碼段鎖定,即可解決互斥鎖存在的問(wèn)題.
QReadWriteLock 讀寫同步線程鎖
該鎖允許用戶以同步讀lockForRead()或同步寫lockForWrite()兩種方式實(shí)現(xiàn)保護(hù)資源,但只要有一個(gè)線程在以寫的方式操作資源,其他線程也會(huì)等待寫入操作結(jié)束后才可繼續(xù)讀資源.
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#include <QCoreApplication>#include <iostream>#include <QThread>#include <QMutex>#include <QReadWriteLock>static QReadWriteLock g_mutex; // 線程鎖static QString g_store; // 定義全局變量class Producer : public QThread{protected: void run() { int count = 0; while(true) { // 以寫入方式鎖定資源 g_mutex.lockForWrite(); g_store.append(QString::number((count++) % 10)); // 寫入后解鎖資源 g_mutex.unlock(); msleep(900); } }};class Customer : public QThread{protected: void run() { while( true ) { // 以讀取方式寫入資源 g_mutex.lockForRead(); if( g_store != "" ) { std::cout << "Curstomer -> "<< g_store.toStdString() << std::endl; } // 讀取到后解鎖資源 g_mutex.unlock(); msleep(1000); } }};int main(int argc, char *argv[]){ QCoreApplication a(argc, argv); Producer p1,p2; Customer c1,c2; p1.setObjectName("producer 1"); p2.setObjectName("producer 2"); c1.setObjectName("curstomer 1"); c2.setObjectName("curstomer 2"); p1.start(); p2.start(); c1.start(); c2.start(); return a.exec();} |
QSemaphore 基于信號(hào)線程鎖
信號(hào)量是特殊的線程鎖,信號(hào)量允許N個(gè)線程同時(shí)訪問(wèn)臨界資源,通過(guò)acquire()獲取到指定資源,release()釋放指定資源.
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#include <QCoreApplication>#include <iostream>#include <QThread>#include <QSemaphore>const int SIZE = 5;unsigned char g_buff[SIZE] = {0};QSemaphore g_sem_free(SIZE); // 5個(gè)可生產(chǎn)資源QSemaphore g_sem_used(0); // 0個(gè)可消費(fèi)資源// 生產(chǎn)者生產(chǎn)產(chǎn)品class Producer : public QThread{protected: void run() { while( true ) { int value = qrand() % 256; // 若無(wú)法獲得可生產(chǎn)資源，阻塞在這里 g_sem_free.acquire(); for(int i=0; i<SIZE; i++) { if( !g_buff[i] ) { g_buff[i] = value; std::cout << objectName().toStdString() << " --> " << value << std::endl; break; } } // 可消費(fèi)資源數(shù)+1 g_sem_used.release(); sleep(2); } }};// 消費(fèi)者消費(fèi)產(chǎn)品class Customer : public QThread{protected: void run() { while( true ) { // 若無(wú)法獲得可消費(fèi)資源，阻塞在這里 g_sem_used.acquire(); for(int i=0; i<SIZE; i++) { if( g_buff[i] ) { int value = g_buff[i]; g_buff[i] = 0; std::cout << objectName().toStdString() << " --> " << value << std::endl; break; } } // 可生產(chǎn)資源數(shù)+1 g_sem_free.release(); sleep(1); } }};int main(int argc, char *argv[]){ QCoreApplication a(argc, argv); Producer p1; Customer c1; p1.setObjectName("producer"); c1.setObjectName("curstomer"); p1.start(); c1.start(); return a.exec();} |
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原文鏈接：https://www.cnblogs.com/LyShark/p/15555343.html
