LINUX线程同步初探

来源：互联网发布：微盘交易源码下载编辑：程序博客网时间：2024/05/22 10:23

0x00.什么是线程同步
　　　　同步，又称直接制约关系，是指多个线程（或进程）为了合作完成任务，必须严格按照规定的某种先后次序来运行

0x01.案例代码

 1 void* PthreadFunc(void* argc); 2 int flag_num = 1; 3  4 int main(int argc, char* argv[]) 5 { 6     pthread_t pid; 7     void* ret_val; 8  9     int create_status = pthread_create(&pid, NULL,  &PthreadFunc, NULL);10     if(0 != create_status)11     {      perror("main()->pthread_create error");12         exit(1);13     }14 15     //input data to public source area16     for(int i = 0;  i < 10; ++i)17     {18         if(flag_num == 1)19         {20             printf("1");21             flag_num = 2;22         }else{23             sleep(1);24         }25     }26 27     int join_status = pthread_join(pid, &ret_val);28     if(0 != join_status)29     {30         perror("main()->pthread_join error");31         exit(1);32     }33 34     //print array's data35     for(int i = 0; i < 10; ++i)36     {37         printf("%d  ", arr[i]);38     }39 40     return 0;41 }42 43 void* PthreadFunc(void* argc)44 {45         if(flag_num == 2)46         {47             printf("2");48             flag_num = 1;49         }else{50             sleep(1);51         }52 }

执行结果:
　　reacher@ubuntu:~/projects/proj$ ./syn
　　1212121212

结论:利用条件避免无休止抢占公共资源

0x02.修改代码获取新知识点 …(⊙_⊙;)

 1 void* PthreadFunc(void* argc); 2 int arr[10]; 3  4 int main(int argc, char* argv[]) 5 { 6     pthread_t pid; 7     void* ret_val; 8  9     int create_status = pthread_create(&pid, NULL,  &PthreadFunc, NULL);10     if(0 != create_status)11     {      perror("main()->pthread_create error");12         exit(1);13     }14 15     //input data to public source area16     for(int i = 0;  i < 10; ++i)17     {18         arr[i] = i;19     }20 21     int join_status = pthread_join(pid, &ret_val);22     if(0 != join_status)23     {24         perror("main()->pthread_join error");25         exit(1);26     }27 28     //print array's data29     for(int i = 0; i < 10; ++i)30     {31         printf("%d  ", arr[i]);32     }33 34     return 0;35 }36 37 void* PthreadFunc(void* argc)38 {39     for(int i = 0;  i < 10; ++i)40     {41         arr[i] = i + 10;42     }43 }

执行代码结果:
reacher@ubuntu:~/projects/proj$ ./syn
10 11 12 13 14 15 16 17 18 19

　　当时出现结果一脸懵,后来查资料发现了线程是有优先级的：main(for()) 属于主线程,PthreadFunc(for())属于子线程、

　　主线程的优先级大于子线程,所以main.for()先对arr进行了数据写入，pthread.for()后写入数据，输出结果为线程输入数据

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