【PTHREAD】线程互斥与同步之栅栏

【PTHREAD】线程互斥与同步之栅栏

栅栏的功能与其字面含义大体相同，阻塞到达栅栏的线程，直到指定数目的线程全部到达。

1 栅栏属性类型

#define __SIZEOF_PTHREAD_BARRIERATTR_T 4
typedef union
{char __size[__SIZEOF_PTHREAD_BARRIERATTR_T];int __align;
} pthread_barrierattr_t;

2 初始化与销毁栅栏属性

int pthread_barrierattr_destroy(pthread_barrierattr_t *attr);
int pthread_barrierattr_init(pthread_barrierattr_t *attr);

3 栅栏属性之进程共享属性

int pthread_barrierattr_getpshared(const pthread_barrierattr_t*restrict attr, int *restrict pshared);
int pthread_barrierattr_setpshared(pthread_barrierattr_t *attr,int pshared);

• PTHREAD_PROCESS_SHARED

  能够访问栅栏内存的所有线程

• PTHREAD_PROCESS_PRIVATE

  创建栅栏所在的进程内的所有线程

4 栅栏结构

# define __SIZEOF_PTHREAD_BARRIER_T 20
typedef union
{char __size[__SIZEOF_PTHREAD_BARRIER_T];long int __align;
} pthread_barrier_t;

5 初始化与销毁栅栏

int pthread_barrier_destroy(pthread_barrier_t *barrier);
int pthread_barrier_init(pthread_barrier_t *restrict barrier,const pthread_barrierattr_t *restrict attr,unsigned count);

6 栅栏等待

int pthread_barrier_wait(pthread_barrier_t *barrier);

7 案例：栅栏的使用

• 源码

  #include <stdio.h>
  #include <stdlib.h>
  #include <unistd.h>
  #include <pthread.h>
  #include <time.h>pthread_barrier_t barrier;void *start_routine_01(void *ptr)
  {printf("子线程(%lu)开始运行...n", pthread_self());printf("子线程(%lu)栅栏等待状态前n", pthread_self());pthread_barrier_wait(&barrier);printf("子线程(%lu)栅栏等待状态后n", pthread_self());printf("子线程(%lu)即将退出...n", pthread_self());return (void*)"9999";
  }void *start_routine_02(void *ptr)
  {printf("子线程(%lu)开始运行...n", pthread_self());printf("子线程(%lu)栅栏等待状态前n", pthread_self());pthread_barrier_wait(&barrier);printf("子线程(%lu)栅栏等待状态后n", pthread_self());printf("子线程(%lu)即将退出...n", pthread_self());return (void*)"9999";
  }void *start_routine_03(void *ptr)
  {printf("子线程(%lu)开始运行...n", pthread_self());printf("子线程(%lu)栅栏等待状态前n", pthread_self());pthread_barrier_wait(&barrier);printf("子线程(%lu)栅栏等待状态后n", pthread_self());printf("子线程(%lu)即将退出...n", pthread_self());return (void*)"9999";
  }int main(int argc, char const *argv[])
  {printf("主线程(%lu)开始运行...n", pthread_self());pthread_barrierattr_t attr;pthread_barrierattr_init(&attr);pthread_barrier_init(&barrier, &attr, 3);pthread_barrier_destroy(&attr);pthread_t thread_id_01;pthread_create(&thread_id_01, NULL, start_routine_01, NULL);pthread_t thread_id_02;pthread_create(&thread_id_02, NULL, start_routine_02, NULL);pthread_t thread_id_03;pthread_create(&thread_id_03, NULL, start_routine_03, NULL);pthread_join(thread_id_01, NULL);pthread_join(thread_id_02, NULL);pthread_join(thread_id_03, NULL);pthread_barrier_destroy(&barrier);printf("主线程(%lu)即将退出...n", pthread_self());exit(EXIT_SUCCESS);
  }
  

• 输出

  主线程(140073106831168)开始运行…
  子线程(140073106827008)开始运行…
  子线程(140073106827008)栅栏等待状态前
  子线程(140073098434304)开始运行…
  子线程(140073098434304)栅栏等待状态前
  子线程(140073090041600)开始运行…
  子线程(140073090041600)栅栏等待状态前
  子线程(140073090041600)栅栏等待状态后
  子线程(140073090041600)即将退出…
  子线程(140073098434304)栅栏等待状态后
  子线程(140073098434304)即将退出…
  子线程(140073106827008)栅栏等待状态后
  子线程(140073106827008)即将退出…
  主线程(140073106831168)即将退出…