C语言创建线程以及使用锁进行读写分离

线程的使用

1.线程的创建

线程的相关操作放在<pthread.h>中。

1.1我们定义一个线程，首先要进行定义一个函数，类似我们创建一个a线程

void *thread_a(void *in){
  printf("Im thread_a\n");
  pthread_exit((void*)0);
}

1.2.创建一个线程

pthread_t a;//声明
pthread_create(&a,NULL,thread_a,(void*)0);//创建线程

1.3.创建3个线程并且打印（如果你打印1000个，并且睡一秒，会发现，这个进程实际上运行是无序的）

#include <stdio.h>
#include <pthread.h>
void *thread_a(void *in){
  printf("Im thread_a\n");
  pthread_exit((void*)0);
}
void *thread_b(void *in){
  printf("Im thread_b\n");
  pthread_exit((void*)0);
}
void *thread_c(void *in){
  printf("Im thread_c\n");
  pthread_exit((void*)0);
}
int main(){
  pthread_t a,b,c;
  int val;
  /**create thread a,b,c*/
  pthread_create(&a,NULL,thread_a,(void*)0);
  pthread_create(&b,NULL,thread_b,(void*)0);
  pthread_create(&c,NULL,thread_c,(void*)0);
  /**main thread waits for termination of a,b,c*/
  pthread_join(a,(void**)0);
  pthread_join(b,(void**)0);
  pthread_join(c,(void**)0);
  printf("Main thread is over\n");
  return 0;
}

3.如果我们希望线程进行打印顺序为c,b,a，那么我们可以定义一个信号。

线程a等待线程2的信号，线程2等待线程3的信号

#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>//sem_wait sem_init这些方法全在里面
sem_t sem1;
sem_t sem2;
void *thread_a(void *in){
  sem_wait(&sem1);/*wait for sem1*/
  printf("Im thread_a\n");
  pthread_exit((void*)0);
}
void *thread_b(void *in){
  sem_wait(&sem2);/*wait for sem2*/
  printf("Im thread_b\n");
  sem_post(&sem1);/*increase sem1 by 1,make thread_a run*/
  pthread_exit((void*)0);
}
void *thread_c(void *in){
  printf("Im thread_c\n");
  sem_post(&sem2);/*increase sem2 by 1,make thread_b run*/
  pthread_exit((void*)0);
}
int main(){
  pthread_t a,b,c;
  int val;
  
  /**init sem1 sem2 to 0,any thread waits for it will be blocked*/
  sem_init(&sem1,0,0);
  sem_init(&sem2,0,0);
  /**create thread a,b,c*/
  pthread_create(&a,NULL,thread_a,(void*)0);  
  pthread_create(&b,NULL,thread_b,(void*)0);  
  pthread_create(&c,NULL,thread_c,(void*)0);  
  /**main thread waits for termination of a,b,c*/  
  pthread_join(a,(void**)0);
  pthread_join(b,(void**)0);
  pthread_join(c,(void**)0);
  printf("Main thread is over\n");
  /*destroy sem1,sem2*/
  sem_destroy(&sem1);
  sem_destroy(&sem2);
  return 0;
}

2.锁的创建和使用

2.1.mutex互斥锁的创建

互斥锁的内容：我们要想创建一个互斥锁，首先是对这个mutex进行初始化操作。

互斥锁的头文件在<pthread.h>中。

pthread_mutex_t mutex;//声明一个锁
pthread_mutex_lock(&mutex);
pthread_mutex_unlock(&mutex);
//加锁和解锁操作
pthread_mutex_destory(&mutex);//销毁锁的操作

2.2.编写一个读写（线程分离)的程序，读一个空串，然后写进另一个数组里面

#include <string.h>
#include <unistd.h>
#include <pthread.h>
#include <stdio.h>

pthread_mutex_t mutex;
char buf[80],buf1[80];
int n,buf_has_item=0;

void writer_function(void){
  while(1){
    pthread_mutex_lock(&mutex);
    if(buf_has_item==0){
      printf("等待从键盘读一个非空串：\n");
      if((n=read(0,buf,sizeof(buf)))>0)
         buf_has_item=1;
      printf("A thread write:%s\n",buf);
    }
    pthread_mutex_unlock(&mutex);
  }
}

void reader_function(void){
  while(1){
    pthread_mutex_lock(&mutex);
    if(buf_has_item==1){
       strcpy(buf1,buf); 
       buf_has_item=0;
       printf("A thread read:%s\n",buf1);
    }     
    pthread_mutex_unlock(&mutex);
  }     
}
             
void *thread_reader(void *in){
  reader_function();
  pthread_exit((void**)0);
}

int main(){
  pthread_t reader,writer;pthread_t ptr;
  pthread_mutex_init(&mutex,NULL);
  pthread_create(&ptr,NULL,thread_reader,(void*)0);//创建一个线程
  writer_function();
  pthread_join(ptr,(void**)0);
  return 0;
}