多线程以及线程同步

cocos2d-x引擎在内部实现了一个庞大的主循环，每帧之间更新界面，如果耗时的操作放到了主线程中，游戏的界面就会卡，这是不能容忍的，游戏最基本的条件就是流畅性，这就是为什么游戏开发选择C++的原因。另外现在双核手机和四核手机越来越普遍了，是时候使用多线程来挖掘硬件的潜力了。

1.环境搭建

cocos2d-x中的多线程使用pthread就可以实现跨平台，而且也不是很难理解。使用pthread需要先配置一下工程。右击工程----->属性----->配置属性---->链接器----->输入---->附加依赖项中添加pthreadVCE2.lib，如下图

接着添加附加包含目录，右击项目，属性----->C/C++---->常规----->附加包含目录加入pthread头文件所在的目录

这样，环境就搭建起来了。

2.多线程的使用

使用pthread来实现多线程，最重要的一个函数是

PTW32_DLLPORT int PTW32_CDECL pthread_create (pthread_t * tid,//线程的标示
                            const pthread_attr_t * attr,      //创建线程的参数
                            void *(*start) (void *),          //入口函数的指针
                            void *arg);                       //传递给线程的数据

在HelloWorldScene.h文件中

pthread_t pidrun,pidgo;
static void* th_run(void *r);
static void* th_go(void *r);

定义了两个函数和两个线程的标识。

然后自定义了一个类，用于给线程传递数据。Student类如下：

#pragma once
#include <string>
class Student
{
public:
    Student(void);
    Student(std::string name,int age,std::string sex);
    ~Student(void);

    std::string name;
    int age;
    std::string sex;

};

源文件如下

#include "Student.h"
#include "cocos2d.h"

Student::Student(void)
{
}


Student::~Student(void)
{
    cocos2d::CCLog("delete data");
}
Student::Student(std::string name,int age,std::string sex)
{
    this->name=name;
    this->age=age;
    this->sex=sex;
}

在退出菜单的回调函数中启动两个线程：

void HelloWorld::menuCloseCallback(CCObject* pSender)
{

    Student *temp=new Student(std::string("zhycheng"),23,std::string("male"));
    pthread_mutex_init(&mutex,NULL);
    pthread_create(&pidrun,NULL,th_run,temp);//启动线程
    pthread_create(&pidgo,NULL,th_go,0);

}

可以看到，将Student的指针传递给了pidrun线程，那么在pidrun线程中获得Student信息如下：

       Student *s=(Student*)(r);
CCLog("name is %s,and age is %d,sex is %s",s->name.c_str(),s->age,s->sex.c_str());
delete s;

3.线程同步

使用了线程，必然就要考虑到线程同步，不同的线程同时访问资源的话，访问的顺序是不可预知的，会造成不可预知的结果。

这里使用pthread_mutex_t来实现同步，下面我来演示一下使用多线程实现卖票系统。卖票的时候，是由多个窗口同时卖票，这里要做到一张票不要卖出去两次，不要出现有票却无法卖的结果。

在线程函数th_run和th_go中来卖票，票的数量是一个全局变量，每卖出去一张票，就将票的数量减一。其中同步的pthread_mutex_t也是一个全局变量，就用它来实现线程同步。

void* HelloWorld::th_run(void *r)
{

    Student *s=(Student*)(r);
    CCLog("name is %s,and age is %d,sex is %s",s->name.c_str(),s->age,s->sex.c_str());
    delete s;
    while(true)
    {
        pthread_mutex_lock(&mutex);
        if(ticket>0)
        {
        CCLog("thread run sell %d",ticket);
        ticket--;
        pthread_mutex_unlock(&mutex);
        }
        else
        {
            pthread_mutex_unlock(&mutex);
            break;
        }

        Sleep(1);
        //Usleep(10);
    }

    return NULL;
}

void* HelloWorld::th_go(void *r)
{

    while(true)
    {
        pthread_mutex_lock(&mutex);
        if(ticket>0)
        {
        CCLog("thread go sell %d",ticket);
        ticket--;
        pthread_mutex_unlock(&mutex);
        }
        else
        {
            pthread_mutex_unlock(&mutex);
            break;

        }

        Sleep(1);

    }
    return NULL;
}

mutex被锁定后，其他线程若再想锁定mutex的话，必须等待，当该线程释放了mutex之后，其他线程才能锁定mutex。Sleep()函数可以使得该线程休眠，单位是毫秒。下面是卖票的结果：

name is zhycheng,and age is 23,sex is male
delete data
thread run sell 100
thread run sell 99
thread go sell 98
thread go sell 97
thread run sell 96
thread go sell 95
thread go sell 94
thread run sell 93
thread go sell 92
thread run sell 91
thread go sell 90
thread go sell 89
thread run sell 88
thread go sell 87
thread run sell 86
thread go sell 85
thread run sell 84
thread go sell 83
thread run sell 82
thread go sell 81
thread run sell 80
thread go sell 79
thread run sell 78
thread go sell 77
thread run sell 76
thread go sell 75
thread run sell 74
thread go sell 73
thread run sell 72
thread go sell 71
thread run sell 70
thread go sell 69
thread go sell 68
thread run sell 67
thread go sell 66
thread run sell 65
thread go sell 64
thread run sell 63
thread go sell 62
thread run sell 61
thread go sell 60
thread run sell 59
thread go sell 58
thread run sell 57
thread go sell 56
thread run sell 55
thread go sell 54
thread run sell 53
thread run sell 52
thread go sell 51
thread run sell 50
thread go sell 49
thread run sell 48
thread go sell 47
thread run sell 46
thread go sell 45
thread run sell 44
thread run sell 43
thread go sell 42
thread run sell 41
thread run sell 40
thread go sell 39
thread run sell 38
thread run sell 37
thread run sell 36
thread run sell 35
thread go sell 34
thread run sell 33
thread run sell 32
thread go sell 31
thread run sell 30
thread run sell 29
thread run sell 28
thread run sell 27
thread run sell 26
thread run sell 25
thread go sell 24
thread run sell 23
thread go sell 22
thread go sell 21
thread run sell 20
thread go sell 19
thread run sell 18
thread run sell 17
thread go sell 16
thread run sell 15
thread go sell 14
thread go sell 13
thread run sell 12
thread go sell 11
thread go sell 10
thread run sell 9
thread go sell 8
thread run sell 7
thread go sell 6
thread go sell 5
thread run sell 4
thread go sell 3
thread run sell 2
thread run sell 1

可以看到，这个打印结果正确无误。如果不加mutex会是什么样的结果呢，我将线程同步的mutex注释掉，输出的结果为：

name is zhycheng,and age is 23,sex is male
delete data
thread run sell 100
thread run sell 99
thread run sell 98
thread go sell 97
thread run sell 96
thread go sell 95
thread run sell 94
thread go sell 94
thread run sell 92
thread run sell 91
thread go sell 90
thread run sell 89
thread go sell 88
thread run sell 87
thread run sell 86
thread go sell 86
thread go sell 84
thread run sell 83
thread go sell 82
thread run sell 81
thread go sell 80
thread run sell 79
thread run sell 78
thread go sell 77
thread run sell 76
thread run sell 75
thread go sell 74
thread run sell 73
thread go sell 72
thread run sell 71
thread go sell 70
thread go sell 69
thread run sell 68
thread go sell 67
thread go sell 66
thread run sell 65
thread go sell 64
thread go sell 63
thread run sell 62
thread go sell 61
thread run sell 60
thread run sell 59
thread run sell 58
thread run sell 57
thread run sell 56
thread run sell 55
thread go sell 54
thread run sell 54
thread go sell 52
thread run sell 52
thread go sell 50
thread run sell 50
thread go sell 49
thread run sell 47
thread go sell 47
thread go sell 45
thread run sell 45
thread run sell 43thread go sell 43

thread run sell 41
thread go sell 41
thread go sell 39
thread run sell 39
thread run sell 37
thread go sell 37
thread go sell 35
thread run sell 35
thread go sell 33thread run sell 33

thread go sell 31thread run sell 31

thread go sell 29
thread run sell 29
thread go sell 27
thread run sell 27
thread go sell 25
thread run sell 25
thread run sell 23
thread go sell 23
thread run sell 21
thread go sell 21
thread go sell 19
thread run sell 19
thread run sell 17
thread go sell 17
thread go sell 15
thread run sell 15
thread run sell 13
thread go sell 13
thread run sell 11thread go sell 11

thread go sell 9
thread run sell 9
thread run sell 7
thread go sell 7
thread go sell 5thread run sell 5

thread go sell 3
thread run sell 3
thread go sell 1
thread run sell 1

可以看到，有的票卖了两次，有的票就没卖。

4.注意

1.Sleep()函数是使得线程休眠的函数，这个函数不跨平台，仅仅在windows上能用，其他平台使用usleep。

2.在非主线程中不能使用cocos2d-x管理内存的CCObject::retain(), CCObject::release() 者CCObject::autorelease()，因为CCAutoreleasePool不是线程安全的，OPENGL的上下文也不是线程安全的，所以不要再非主线程中使用cocos2d-x的API和UI操作。

最后工程的源代码下载：http://download.csdn.net/detail/zhy_cheng/5600979

转自：http://blog.csdn.net/zhy_cheng/article/details/9116479