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C/C++ Pthread线程

时间:2018-07-18 23:40:19      阅读:325      评论:0      收藏:0      [点我收藏+]

标签:sem   printf   队列   try   常用   设置   exit   adc   div   

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 = 0;
    int count = 0;
    printf("Thread %d is starting\n", thrd_num);
    for (count = 0; count < REPEAT_NUMBER; count++) {
        delay_time = (int)(rand() * DELAY_TIME_LEVELS/(RAND_MAX)) + 1;
        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 = 0, res;
     void * thrd_ret;
     srand(time(NULL));    
     for (no = 0; no < THREAD_NUMBER; no++) {
          /* 创建多线程 */
          res = pthread_create(&thread[no], NULL, thrd_func, (void*)no);
          if (res != 0) {
               printf("Create thread %d failed\n", no);
               exit(res);
          }
     }

     printf("Create treads success\n Waiting for threads to finish...\n");
     for (no = 0; 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 0;        
}

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 0 is starting
Thread 1 is starting
Thread 2 is starting
Thread 1: job 0 delay = 2
Thread 1: job 1 delay = 2
Thread 0: job 0 delay = 8
Thread 2: job 0 delay = 10
Thread 2: job 1 delay = 3
Thread 1: job 2 delay = 10
Thread 0: job 1 delay = 8
Thread 0: job 2 delay = 3
Thread 0: job 3 delay = 1
Thread 2: job 2 delay = 8
Thread 1: job 3 delay = 8
Thread 1: job 4 delay = 1
Thread 1 finished
        Thread 2: job 3 delay = 6
        Thread 0: job 4 delay = 7
Thread 0 finished
Thread 0 joined
Thread 1 joined
        Thread 2: job 4 delay = 10
Thread 2 finished
Thread 2 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 = 0, count = 0;
     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 = 0; count < REPEAT_NUMBER; count++) {          
         delay_time = (int)(rand() * DELAY_TIME_LEVELS/(RAND_MAX)) + 1;
         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 = 0, res;
     void * thrd_ret;

     srand(time(NULL));
     /* 互斥锁初始化 */
     pthread_mutex_init(&mutex, NULL);
     for (no = 0; no < THREAD_NUMBER; no++) {
          res = pthread_create(&thread[no], NULL, thrd_func, (void*)no);
          if (res != 0) {
              printf("Create thread %d failed\n", no);
              exit(res);
          }
     }     
     printf("Create treads success\n Waiting for threads to finish...\n");
     for (no = 0; 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 0;        
}

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 0 is starting
        Thread 0: job 0 delay = 9
        Thread 0: job 1 delay = 4
        Thread 0: job 2 delay = 7
Thread 0 finished
Thread 0 joined
Thread 1 is starting
        Thread 1: job 0 delay = 6
        Thread 1: job 1 delay = 4
        Thread 1: job 2 delay = 7
Thread 1 finished
Thread 1 joined
Thread 2 is starting
        Thread 2: job 0 delay = 3
        Thread 2: job 1 delay = 1
        Thread 2: job 2 delay = 6
Thread 2 finished
Thread 2 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 = 0;
    int count = 0;
    sem_wait(&sem[thrd_num]);
    printf("Thread %d is starting\n", thrd_num);
    for (count = 0; count < REPEAT_NUMBER; count++) {
        delay_time = (int)(rand() * DELAY_TIME_LEVELS/(RAND_MAX)) + 1;
        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 = 0, res;
    void * thrd_ret;
    srand(time(NULL));
    for (no = 0; no < THREAD_NUMBER; no++) {
        sem_init(&sem[no], 0, 0);
        res = pthread_create(&thread[no], NULL, thrd_func, (void*)no);
        if (res != 0) {
            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 - 1]);
    for (no = THREAD_NUMBER - 1; no >= 0; 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 - 1) % THREAD_NUMBER]);           
    }

    for (no = 0; no < THREAD_NUMBER; no++) {
        sem_destroy(&sem[no]);      
    }
    return 0;        
}

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 2 is starting
        Thread 2: job 0 delay = 9
        Thread 2: job 1 delay = 9
        Thread 2: job 2 delay = 5
Thread 2 finished
Thread 2 joined
Thread 1 is starting
        Thread 1: job 0 delay = 5
        Thread 1: job 1 delay = 7
        Thread 1: job 2 delay = 4
Thread 1 finished
Thread 1 joined
Thread 0 is starting
        Thread 0: job 0 delay = 3
        Thread 0: job 1 delay = 9
        Thread 0: job 2 delay = 8
Thread 0 finished
Thread 0 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 = 0;

void * thrd_func(void * arg){
    int delay_time = 0;
    int count = 0;
    printf("Thread is starting\n");
    for (count = 0; count < REPEAT_NUMBER; count++) {
        delay_time = (int)(rand() * DELAY_TIME_LEVELS/(RAND_MAX)) + 1;
        sleep(delay_time);
        printf("\tThread : job %d delay = %d\n", count, delay_time);
    }
    printf("Thread finished\n");
    finish_flag = 1;
    pthread_exit(NULL);
}

int main(void) {
    pthread_t thread;
    pthread_attr_t attr;
    int res = 0;
    srand(time(NULL));
    res = pthread_attr_init(&attr);
    if (res != 0) {
        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 != 0) {
        printf("Setting attribute failed\n");
        exit(res);
    }
    res = pthread_create(&thread, &attr, thrd_func, NULL);
    if (res != 0) {
        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(2);
    }
    return 0;        
}

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。

C/C++ Pthread线程

标签:sem   printf   队列   try   常用   设置   exit   adc   div   

原文地址:https://www.cnblogs.com/zhangjiansheng/p/9332799.html

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