六、linux多线程操作

pthread线程库
线程操作，包括线程的创建，线程的设置，线程同步，线程取消等操作。程序中多线程操作多适用于同时执行某些任务的情况下。一般将需要进行的任务写入某些函数定义，以该函数为载体，创建线程，执行完毕后返回一个结果，与函数的区别就是，执行函数时，调用者会被阻塞直到函数执行完毕，但线程运行时主线程不会被阻塞。
要点
理解线程操作函数，包括pthread_create/pthread_exit/pthread_cancel，使用man查看该系列函数帮助

一个创建线程的简单事例

#include
#include
#include
#include
#include
#include
char message[50] = "THREAD_TEST";
void* thread_func(void *arg);
int main(){
    pthread_t t_thread;
    void *thread_result;
    int res;
    res = pthread_create(&t_thread, NULL, thread_func, (void*)message);
    if(res != 0){
        perror("线程创建失败！");
        exit(EXIT_FAILURE);
    }
    printf("wait for the thread!\n");
    pthread_join(t_thread, &thread_result);
    printf("线程已结束，返回值为%s\n", (char*)thread_result);
    printf("message的值为%s\n", message);
    free(thread_result);
    exit(EXIT_SUCCESS);
}

void* thread_func(void *arg){
    printf("线程正在运行，参数为%s\n", (char*)arg);
    sleep(3);
    strcpy(message, "线程修改");
    char* buf = (char*)malloc(strlen("线程执行完毕！"));
    strcpy(buf, "线程执行完毕！");
    pthread_exit(buf);
}

一个取消线程的简单事例

#include
#include
#include
#include
#include
void *thread_func(void *arg){
    int res;
    res = pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
    if(res != 0){
        perror("设置线程取消失败");
        exit(EXIT_FAILURE);
    }
    if((res = pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, NULL)) != 0){
        perror("设置线程取消类型失败！");
        exit(EXIT_FAILURE);
    }
    printf("子线程正在运行！\n");
    for(int i = 0; i < 10; i++){
        sleep(1);
        printf("子线程正在运行！\n");
    }
    pthread_exit(EXIT_SUCCESS);
}
int main(){
    int res;
    pthread_t thread;
    if((res = pthread_create(&thread, NULL, thread_func, NULL)) != 0){
        perror("线程创建失败！");
        exit(EXIT_FAILURE);
    }
    sleep(3);
    printf("取消线程！\n");
    if((res = pthread_cancel(thread)) != 0){
        perror("取消线程失败！");
        exit(EXIT_FAILURE);
    }
    exit(EXIT_SUCCESS);
}

进程同步使用信号量与互斥量
信号量
掌握理解操作信号量的函数调用sem_init/sem_post/sem_wait/sem_destory，一个简单事例

#include
#include
#include
#include
#include
#include
//thread_func declaration
void *thread_func(void* arg);
//semaphore global var
sem_t semth;
//buff used to receive the user input
#define BUFSIZE 1024
char buf[BUFSIZE];
//man function
int main(){
    //var declaration:int res, pthread_t used to create pthread,void thread_res used to join
    int res;
    pthread_t thread;
    void *thread_res;

    if((res = sem_init(&semth, 0, 0)) != 0){
        perror("create semaphore failed");
        exit(EXIT_FAILURE);
    }
//pthread create with error detection
    if((res = pthread_create(&thread, NULL, thread_func, NULL)) != 0){
        perror("create thread failed");
        exit(EXIT_FAILURE);
    }
//prompt information
    printf("Please input string information and type 'end' to exit!");
//get user input and make a P operation on sem_t
    while(strncmp(buf, "end", 3) != 0){
        fgets(buf, BUFSIZE, stdin);
        sem_post(&semth);
    }
//join the thread
    if((res = pthread_join(thread, &thread_res)) != 0){
        perror("thread join failed");
        exit(EXIT_FAILURE);
    }
//destory the semaphore
    if((res = sem_destroy(&semth)) != 0){
        perror("destory semaphore failed");
        exit(EXIT_FAILURE);
    }
//exit
    exit(EXIT_SUCCESS);
}

//thread_func definition
void *thread_func(void *arg){
//make V operation on sem_t
    sem_wait(&semth);
//while loop , get user info from buff, and make V operation on sem_t
    while(strncmp(buf, "end", 3) != 0){
        printf("you type:%s\n", buf);
        sem_wait(&semth);
    }
    fputs("exiting...\n", stdout);
//pthread_exit
    pthread_exit(0);
}

result

使用互斥量进行数据同步
理解互斥量的概念，掌握相关系统调用。
pthread_mutex_init/pthread_mutex_lock/pthread_mutex_unlock/pthread_mutex_destory
一个简单的示例如下

#include

#include

#include
#include
#include
#include
// global var declaration
pthread_mutex_t mutex;//global mutex lock
int exit_time = 1;//running symbol
char work_area[1024];
void* thread_func(void* arg){
    printf("子线程正在执行，对互斥量加锁\n");
    pthread_mutex_lock(&mutex);
    while(strncmp(work_area, "end", 3) != 0){
        printf("len:%d\n", strlen(work_area) - 1);
        work_area[0] = '\0';
        printf("解锁互斥量\n");
        pthread_mutex_unlock(&mutex);
        puts("睡眠1秒！\n");
        sleep(1);
        printf("判断信息是否为空\n");
        
        while(work_area[0] == '\0'){
            printf("轮询直到有信息传送！\n");
            if(work_area[0] == '\0'){
                sleep(1);
            }else{
                pthread_mutex_lock(&mutex);
                break;
            }
            
        }
    }
    exit_time = 0;
    work_area[0] = '\0';
    pthread_mutex_unlock(&mutex);
    pthread_exit(EXIT_SUCCESS);
}

int main(){
    pthread_t thread;
    int res;
    void * thread_res;
    
    pthread_mutex_init(&mutex, NULL);
    pthread_mutex_lock(&mutex);
    if((res = pthread_create(&thread, NULL, thread_func, NULL)) != 0){
        perror("创建线程失败！");
        exit(EXIT_FAILURE);
    }
    
    while(exit_time){
        printf("type your string:\n");
        fgets(work_area, 1024, stdin);
        pthread_mutex_unlock(&mutex);
        while(1){
            if(work_area[0] != '\0'){
                puts("数据未被取出");
                sleep(1);
            }else{

                pthread_mutex_lock(&mutex);
                break;

            }
        }
        
    }
    pthread_mutex_unlock(&mutex);
    printf("wait for the thread exit!\n");
    if((res = pthread_join(thread, thread_res)) != 0){
        perror("等待线程结束出错！");
        exit(EXIT_FAILURE);
    }
    printf("thread exited!");
    pthread_mutex_destroy(&mutex);
    exit(EXIT_SUCCESS);
}

六、linux多线程操作

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