C/C++ Pthread线程

线程按照其调度者可以分为用户级线程和核心级线程两种 
用户级线程主要解决的是上下文切换的问题，它的调度算法和调度过程全部由用户自行选择决定，在运行时不需要特定的内核支持； 
我们常用基本就是用户级线程，所以就只总结一下POSIX提供的用户级线程接口； 
基本线程操作相关的函数： 
1线程的建立结束 
2线程的互斥和同步 
3使用信号量控制线程 
4线程的基本属性配置

基本线程操作：

函数	说明
pthread_create()	创建线程开始运行相关线程函数，运行结束则线程退出
pthread_eixt()	因为exit()是用来结束进程的，所以则需要使用特定结束线程的函数
pthread_join()	挂起当前线程，用于阻塞式地等待线程结束，如果线程已结束则立即返回，0=成功
pthread_cancel()	发送终止信号给thread线程，成功返回0，但是成功并不意味着thread会终止
pthread_testcancel()	在不包含取消点，但是又需要取消点的地方创建一个取消点，以便在一个没有包含取消点的执行代码线程中响应取消请求.
pthread_setcancelstate()	设置本线程对Cancel信号的反应
pthread_setcanceltype()	设置取消状态 继续运行至下一个取消点再退出或者是立即执行取消动作
pthread_setcancel()	设置取消状态

互斥与同步机制基本函数

函数	说明
pthread_mutex_init()	互斥锁的初始化
pthread_mutex_lock()	锁定互斥锁，如果尝试锁定已经被上锁的互斥锁则阻塞至可用为止
pthread_mutex_trylock()	非阻塞的锁定互斥锁
pthread_mutex_unlock()	释放互斥锁
pthread_mutex_destory()	互斥锁销毁函数

信号量线程控制(默认无名信号量)

函数	说明
sem_init(sem)	初始化一个定位在sem的匿名信号量
sem_wait()	把信号量减1操作，如果信号量的当前值为0则进入阻塞，为原子操作
sem_trywait()	如果信号量的当前值为0则返回错误而不是阻塞调用(errno=EAGAIN),其实是sem_wait()的非阻塞版本
sem_post()	给信号量的值加1，它是一个“原子操作”，即同时对同一个信号量做加1,操作的两个线程是不会冲突的
sem_getvalue(sval)	把sem指向的信号量当前值放置在sval指向的整数上
sem_destory(sem)	销毁由sem指向的匿名信号量

线程属性配置相关函数

函数	说明
pthread_attr_init()	初始化配置一个线程对象的属性,需要用pthread_attr_destroy函数去除已有属性
pthread_attr_setscope()	设置线程属性
pthread_attr_setschedparam()	设置线程优先级
pthread_attr_getschedparam()	获取线程优先级

基本的线程建立运行pthread_create

/* thread.c */
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

#define THREAD_NUMBER       3                 /*线程数*/
#define REPEAT_NUMBER       5                 /*每个线程中的小任务数*/
#define DELAY_TIME_LEVELS  10.0             /*小任务之间的最大时间间隔*/
//
void *thrd_func(void *arg) {
    /* 线程函数例程 */
    int thrd_num = (int)arg;
    int delay_time = ;
    int count = ;
    printf("Thread %d is starting\n", thrd_num);
    for (count = ; count < REPEAT_NUMBER; count++) {
        delay_time = (int)(rand() * DELAY_TIME_LEVELS/(RAND_MAX)) + ;
        sleep(delay_time);
        printf("\tThread %d: job %d delay = %d\n",
                      thrd_num, count, delay_time);
    }

    printf("Thread %d finished\n", thrd_num);
    pthread_exit(NULL);
}

int main(void) {
     pthread_t thread[THREAD_NUMBER];
     int no = , res;
     void * thrd_ret;
     srand(time(NULL));
     for (no = ; no < THREAD_NUMBER; no++) {
          /* 创建多线程 */
          res = pthread_create(&thread[no], NULL, thrd_func, (void*)no);
          if (res != ) {
               printf("Create thread %d failed\n", no);
               exit(res);
          }
     }

     printf("Create treads success\n Waiting for threads to finish...\n");
     for (no = ; no < THREAD_NUMBER; no++) {
          /* 等待线程结束 */
          res = pthread_join(thread[no], &thrd_ret);
          if (!res) {
            printf("Thread %d joined\n", no);
          } else {
            printf("Thread %d join failed\n", no);
          }
     }
     return ;
}

例程中循环3次建立3条线程，并且使用pthread_join函数依次等待线程结束； 
线程中使用rand()获取随机值随机休眠5次，随意会出现后执行的线程先执行完成； 
运行结果：

$ gcc thread.c -lpthread
$ ./a.out
Create treads success
 Waiting for threads to finish...
Thread  is starting
Thread  is starting
Thread  is starting
Thread : job  delay =
Thread : job  delay =
Thread : job  delay =
Thread : job  delay =
Thread : job  delay =
Thread : job  delay =
Thread : job  delay =
Thread : job  delay =
Thread : job  delay =
Thread : job  delay =
Thread : job  delay =
Thread : job  delay =
Thread  finished
        Thread : job  delay =
        Thread : job  delay =
Thread  finished
Thread  joined
Thread  joined
        Thread : job  delay =
Thread  finished
Thread  joined

可以看到，线程1先于线程0执行，但是pthread_join的调用时间顺序，先等待线程0执行； 
由于线程1已经早结束，所以线程0被pthread_join等到的时候，线程1已结束，就在等待到线程1时，直接返回；

线程执行的互斥和同步pthread_mutex_lock

在上面的程序中增加互斥锁

/*thread_mutex.c*/
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

#define THREAD_NUMBER        3            /* 线程数 */
#define REPEAT_NUMBER        3            /* 每个线程的小任务数 */
#define DELAY_TIME_LEVELS 10.0         /*小任务之间的最大时间间隔*/
pthread_mutex_t mutex;

void *thrd_func(void *arg) {
     int thrd_num = (int)arg;
     int delay_time = , count = ;
     int res;
     /* 互斥锁上锁 */
     res = pthread_mutex_lock(&mutex);
     if (res) {
          printf("Thread %d lock failed\n", thrd_num);
          pthread_exit(NULL);
     }
     printf("Thread %d is starting\n", thrd_num);
     for (count = ; count < REPEAT_NUMBER; count++) {
         delay_time = (int)(rand() * DELAY_TIME_LEVELS/(RAND_MAX)) + ;
         sleep(delay_time);
         printf("\tThread %d: job %d delay = %d\n",
                                      thrd_num, count, delay_time);
     }
     printf("Thread %d finished\n", thrd_num);
     pthread_exit(NULL);
}

int main(void) {
     pthread_t thread[THREAD_NUMBER];
     int no = , res;
     void * thrd_ret;

     srand(time(NULL));
     /* 互斥锁初始化 */
     pthread_mutex_init(&mutex, NULL);
     for (no = ; no < THREAD_NUMBER; no++) {
          res = pthread_create(&thread[no], NULL, thrd_func, (void*)no);
          if (res != ) {
              printf("Create thread %d failed\n", no);
              exit(res);
          }
     }
     printf("Create treads success\n Waiting for threads to finish...\n");
     for (no = ; no < THREAD_NUMBER; no++) {
          res = pthread_join(thread[no], &thrd_ret);
          if (!res) {
                printf("Thread %d joined\n", no);
          } else  {
              printf("Thread %d join failed\n", no);
          }
     }
     /****互斥锁解锁***/
     pthread_mutex_unlock(&mutex);
     pthread_mutex_destroy(&mutex);
     return ;
}

在上面的例程中直接添加同步锁pthread_mutex_t； 
在线程中加入，于是程序在执行线程程序时； 
调用pthread_mutex_lock上锁，发现上锁时候后进入等待，等待锁再次释放后重新上锁； 
所以线程程序加载到队列中等待，等待成功上锁后继续执行程序代码； 
运行结果

$gcc thread_mutex.c -lpthread
$ ./a.out
Create treads success
 Waiting for threads to finish...
Thread  is starting
        Thread : job  delay =
        Thread : job  delay =
        Thread : job  delay =
Thread  finished
Thread  joined
Thread  is starting
        Thread : job  delay =
        Thread : job  delay =
        Thread : job  delay =
Thread  finished
Thread  joined
Thread  is starting
        Thread : job  delay =
        Thread : job  delay =
        Thread : job  delay =
Thread  finished
Thread  joined

跟例程1中执行结果不同，线程程序被加载到队列中而不能马上执行，需要等到能够成功上锁； 
上锁后，继续执行线程程序，上锁执行； 
这样线程被依次执行的情况在实际使用场景中经常出现； 
使用场景： 
当用户登录后获取秘钥才能继续获取该用户的基本信息时；需要等待登录线程结束后才能继续执行获取用户信息的线程时， 
需要调用两条线程，假如是：threadLogin(),threadGetInfo(); 则可以有2种方法实现： 
1 此时可以使用互斥锁同时一次性调用完threadLogin()和threadGetInfo()； 
2 当然也可以不使用互斥锁直接在threadLogin()中登录验证成功后调用threadGetInfo()； 
相比之下，方式1更加清晰的显示逻辑关系，增加代码可读性可扩展性。

使用信号量控制线程的执行顺序sem_post

修改上面例程，上面的是使用pthread_mutex_lock互斥锁控制线程执行顺序， 
使用另外一种线程执行顺序的控制；

/* thread_sem.c */
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>

#define THREAD_NUMBER       3
#define REPEAT_NUMBER       3
#define DELAY_TIME_LEVELS   10.0

sem_t sem[THREAD_NUMBER];

void * thrd_func(void *arg) {
    int thrd_num = (int)arg;
    int delay_time = ;
    int count = ;
    sem_wait(&sem[thrd_num]);
    printf("Thread %d is starting\n", thrd_num);
    for (count = ; count < REPEAT_NUMBER; count++) {
        delay_time = (int)(rand() * DELAY_TIME_LEVELS/(RAND_MAX)) + ;
        sleep(delay_time);
        printf("\tThread %d: job %d delay = %d\n", thrd_num, count, delay_time);
    }
    printf("Thread %d finished\n", thrd_num);
    pthread_exit(NULL);
}

int main(void) {
    pthread_t thread[THREAD_NUMBER];
    int no = , res;
    void * thrd_ret;
    srand(time(NULL));
    for (no = ; no < THREAD_NUMBER; no++) {
        sem_init(&sem[no], , );
        res = pthread_create(&thread[no], NULL, thrd_func, (void*)no);
        if (res != ) {
            printf("Create thread %d failed\n", no);
            exit(res);
        }
    }

    printf("Create treads success\n Waiting for threads to finish...\n");
    sem_post(&sem[THREAD_NUMBER - ]);
    for (no = THREAD_NUMBER - ; no >= ; no--) {
        res = pthread_join(thread[no], &thrd_ret);
        if (!res) {
            printf("Thread %d joined\n", no);
        } else {
            printf("Thread %d join failed\n", no);
        }
        sem_post(&sem[(no + THREAD_NUMBER - ) % THREAD_NUMBER]);
    }

    for (no = ; no < THREAD_NUMBER; no++) {
        sem_destroy(&sem[no]);
    }
    return ;
}

执行结果，仍然是建立3条线程，每条线程执行时休眠随机时长：

$ gcc thread_sem.c -lpthread
$ ./a.out
Create treads success
 Waiting for threads to finish...
Thread  is starting
        Thread : job  delay =
        Thread : job  delay =
        Thread : job  delay =
Thread  finished
Thread  joined
Thread  is starting
        Thread : job  delay =
        Thread : job  delay =
        Thread : job  delay =
Thread  finished
Thread  joined
Thread  is starting
        Thread : job  delay =
        Thread : job  delay =
        Thread : job  delay =
Thread  finished
Thread  joined

执行结果与第2个例程非常相似，只不过教材中进行倒序执行而已； 
那么这种方式其实与使用互斥锁相比，代码量可读性基本持平不相上下；

线程的基本属性pthread_attr_setscope

设置属性一般有： 
1 绑定属性 
2 分离属性 
3 堆栈地址 
4 堆栈大小 
5 优先级

关于绑定属性就是绑定于内核线程； 
分离属性主要是讲线程结束后是否马上释放相应的内存；

/* thread_attr.c */
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

#define THREAD_NUMBER       1
#define REPEAT_NUMBER       3
#define DELAY_TIME_LEVELS   10.0
int finish_flag = ;

void * thrd_func(void * arg){
    int delay_time = ;
    int count = ;
    printf("Thread is starting\n");
    for (count = ; count < REPEAT_NUMBER; count++) {
        delay_time = (int)(rand() * DELAY_TIME_LEVELS/(RAND_MAX)) + ;
        sleep(delay_time);
        printf("\tThread : job %d delay = %d\n", count, delay_time);
    }
    printf("Thread finished\n");
    finish_flag = ;
    pthread_exit(NULL);
}

int main(void) {
    pthread_t thread;
    pthread_attr_t attr;
    int res = ;
    srand(time(NULL));
    res = pthread_attr_init(&attr);
    if (res != ) {
        printf("Create attribute failed\n");
        exit(res);
    }
    res = pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM);
    res += pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
    if (res != ) {
        printf("Setting attribute failed\n");
        exit(res);
    }
    res = pthread_create(&thread, &attr, thrd_func, NULL);
    if (res != ) {
        printf("Create thread failed\n");
        exit(res);
    }
    pthread_attr_destroy(&attr);
    printf("Create tread success\n");

    while(!finish_flag){
        printf("Waiting for thread to finish...\n");
        sleep();
    }
    return ;
}

在运行前后使用 $ free 命令查看内存前后的使用情况发现： 
在线程结束后内存马上被释放；
其实，一般线程的属性直接使用系统默认属性即可； 
关于线程的使用，大约就是这样。