OpenThreads线程管理

OpenSceneGraph中线程（OpenThreads）的作用多种多样，涉及到信号量机制，同步异步锁等多种知识点。

OpenThreads： Threads：创建线程，类似于windows中的_beginthread, Mutex ：创建互斥，类似于windows中的CreateMutex，用于针对多个线程访问同一资源 情况。 Condition：创建条件，用于符合条件时才启动某个线程，使用Mutex实现。 Barrier ：创建壁垒，用于同步线程，比如某操作必须前面几个线程完成时才能进行。

线程调用大致分为四个方法：

其一：运用Windows.h的线程方法，通过创建线程函数，进行线程的调用以及信号量机制的占用以及 释放。这里用两个进程买票的例子。 #include <process.h> #include <Windows.h> #include <iostream>

int tickets = 10; HANDLE iMutex;//创建一个句柄 void sellTickets1(void *ptr) { while (tickets > 0) { //等待信号量 WaitForSingleObject(iMutex, INFINITE); Sleep(10); std::cout << "Thread1 sell : " << tickets << std::endl; tickets--; //释放信号量 ReleaseMutex(iMutex); } } void sellTickets2(void *ptr) { while (tickets > 0) { //等待信号量 WaitForSingleObject(iMutex, INFINITE); Sleep(10); std::cout << "Thread2 sell : " << tickets << std::endl; tickets--; //释放信号量 ReleaseMutex(iMutex); } }

int main() { //创建一个线程，线程调用sellTickets1函数 HANDLE t1 = (HANDLE)_beginthread(&sellTickets1, 0, 0); //创建一个线程，线程调用sellTickets2函数 HANDLE t2 = (HANDLE)_beginthread(&sellTickets2, 0, 0); //创建一个信号量，用于互斥对象 iMutex = (HANDLE)CreateMutex(0, FALSE, 0); Sleep(2000); system("pause"); return 0; }

其二：通过实例化继承Thread的类的对象，然后将其调用start函数，启动线程，通过调用 ScopedLock函数规定其线程在这个范围内执行结束后才能释放，其余线程处于等待时间。 #include <OpenThreads/ScopedLock> #include <OpenThreads/Mutex> #include <OpenThreads/Thread> #include <iostream> #include <Windows.h>

OpenThreads::Mutex mutex; class ThreadSelf : public OpenThreads::Thread { public: ThreadSelf(int a) { threadid = a; } virtual ~ThreadSelf() { while (isRunning()) OpenThreads::Thread::YieldCurrentThread(); } void run() { //只有在下边的全部运行之后，才会将下一个进程纳入运行 OpenThreads::ScopedLock<OpenThreads::Mutex> lock(mutex); int count = 10; while (--count) { Sleep(10); std::cout <<"Thread print:"<< threadid << std::endl; } } int threadid; }; int main() { ThreadSelf t1(10); ThreadSelf t2(6); t1.start(); t2.start(); Sleep(3000); system("pause"); return 1; }

其三：通过实例化继承Thread的类的对象，然后将其调用start函数，启动线程，通过调用 block（n）函数规定其之前的n个线程完成时后才能执行之后的程序，否则将一直处于等待时 间。n从0开始，如果进程执行次数大于所给数字，就会冲破壁垒，然后执行下边的进程。 #include <OpenThreads/Thread> #include <OpenThreads/Barrier> #include <iostream> #include <Windows.h>

OpenThreads::Barrier bar; class ThreadSelf : public OpenThreads::Thread { public: ThreadSelf(int a) { threadid = a; } virtual ~ThreadSelf() { while (isRunning()) OpenThreads::Thread::YieldCurrentThread(); } void run() { int count = 10; while (--count) { Sleep(10); std::cout <<"Thread print:"<< threadid << std::endl; } bar.block(); } int threadid; }; int main() { ThreadSelf t1(10); ThreadSelf t2(6); t1.start(); bar.block(2); t2.start(); bar.block(0); std::cout << "Here" << std::endl; Sleep(3000); system("pause"); return 1; }

其四：运用Windows.h的线程方法，通过_beginthread创建线程函数，通过Condition定义的对象 cont来进行信号量的等待以及释放，通过Mutex来作为条件，运用signal函数以及wait函数进 行线程的管理。 #include <iostream> #include <process.h> #include <OpenThreads/Condition> #include <Windows.h>

int condition = 0; OpenThreads::Condition cont; OpenThreads::Mutex mutex; void setCondition(void *ptr) { condition = 1; cont.signal(); } void ifCondition(void *ptr) { cont.wait(&mutex, INFINITE); if (condition) std::cout << "Condifion os find" << std::endl; }

int main() { HANDLE t1 = (HANDLE)_beginthread(&ifCondition, 0, 0); HANDLE t2 = (HANDLE)_beginthread(&setCondition, 0, 0); Sleep(1000); std::cout << "END" << std::endl; system("pause"); return 0; }