两个线程,一个线程打印A,一个线程打印B,如何实现两个线程按顺序打印出ABABAB

方法一：信号量
类似于生产者和消费者问题

#include 
#include 
#include 
#include 
sem_t blank_number, product_number;
 
void *producer(void *arg)
{
    while (1) {
        sem_wait(&blank_number);//给blank_number信号量减1，如果blank_number为0，在这里阻塞，直到blank_number不为0
        printf("%c\n",65);
        sem_post(&product_number);//给product_number加1
        sleep(rand()%5);
    }
}
void *consumer(void *arg)
{
    while (1) {
        sem_wait(&product_number);
        printf("%c\n",66);
        sem_post(&blank_number);
        sleep(rand()%5);
}
}
int main(int argc, char *argv[])
{
    pthread_t pid, cid;
    sem_init(&blank_number, 0, 1);//对信号量进行初始化
    sem_init(&product_number, 0, 0);
    pthread_create(&pid, NULL, producer, NULL);
    pthread_create(&cid, NULL, consumer, NULL);
    pthread_join(pid, NULL);//回收线程，当然这块两个线程由于一直在while循环，线程会一直阻塞在这句话
    pthread_join(cid, NULL);
    sem_destroy(&blank_number);//销毁信号量
    sem_destroy(&product_number);
    return 0;
}

方法二、互斥量

#include 
#include 
#include 
#include 
 
pthread_mutex_t mutex;
int flag=1;//因为是linux下c语言实现的，所以不能写成bool flag=true;因为bool类型是C++新增的类型
void *printA(void *arg)
{
    while (1) {
        pthread_mutex_lock(&mutex);
        if(flag==1)
	        printf("%c\n",65);
        flag=0;
        pthread_mutex_unlock(&mutex);
        sleep(rand()%5);
    }
}
void *printB(void *arg)
{
    while (1) {
        pthread_mutex_lock(&mutex);
        if(flag==0)
        	printf("%c\n",66);
        flag=1;
        pthread_mutex_unlock(&mutex);
        sleep(rand()%5);
    }
}
int main(int argc, char *argv[])
{
    pthread_t aid, bid;
 
    pthread_mutex_init(&mutex,NULL);
    pthread_create(&aid, NULL, printA, NULL);//创建线程
    pthread_create(&bid, NULL, printB, NULL);
    pthread_join(aid, NULL);//回收线程
    pthread_join(bid, NULL);
 
    pthread_mutex_destroy(&mutex);//销毁互斥量
    return 0;