编写一个程序，开启3个线程，这3个线程的ID分别为A、B、C，每个线程将自己的ID在屏幕上打印10遍，要求输出结果必须按ABC的顺序显示；如：ABCABC….依次递推。

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>
#include <string.h>
//#define DEBUG 1
#define NUM 3

int n=0;
pthread_mutex_t mylock=PTHREAD_MUTEX_INITIALIZER;//互斥量
pthread_cond_t qready=PTHREAD_COND_INITIALIZER;//条件变量

void * thread_func(void *arg)
{
int param=(int)arg;
char c='A'+param;
int ret,i=0;
for (; i < 10; i++)
{
pthread_mutex_lock(&mylock);
while (param != n)  //刚运行时，n = 0， param = 0,条件不成立，所以直接打印A
{
#ifdef DEBUG
printf("thread %d waiting\n", param);
#endif
ret = pthread_cond_wait(&qready, &mylock);
if (ret == 0)
{
#ifdef DEBUG
printf("thread %d wait success\n", param);
#endif
} else
{
#ifdef DEBUG
printf("thread %d wait failed:%s\n", param, strerror(ret));
#endif
}
}
// printf("%d ",param+1);
printf("%c ",c);  //打印A后
n=(n+1)%NUM;      //n变成了1，对线程2会产出影响！！！！
pthread_mutex_unlock(&mylock);
//会唤醒所有的线程，因为当这个线程完后会等pthread_cond_wait()执行两次后才能退出while (param != n)
pthread_cond_broadcast(&qready);

}
return (void *)0;
}

#if 0
//假设为线程2

void * thread_func(void *arg)//传入值1
{
int param=(int)arg;
char c='A'+param;
int ret,i=0;
for (; i < 10; i++)
{
pthread_mutex_lock(&mylock);
while (param != n)  //和线程1同时执行 parm = 1，n = 0，所以刚开始时条件满足
{
#ifdef DEBUG
printf("thread %d waiting\n", param);
#endif
//执行到此时，等待线程1发送信号，当线程1的A打印完后，n的值也变成了1，条件就不成立了
ret = pthread_cond_wait(&qready, &mylock);
if (ret == 0)
{
#ifdef DEBUG
printf("thread %d wait success\n", param);
#endif
} else
{
#ifdef DEBUG
printf("thread %d wait failed:%s\n", param, strerror(ret));
#endif
}
}
// printf("%d ",param+1);
printf("%c ",c); //此时打印值B
n=(n+1)%NUM;    //对打印C的线程3产生影响！！！
pthread_mutex_unlock(&mylock);
pthread_cond_broadcast(&qready);
}
return (void *)0;
}

#endif

int main(int argc, char** argv) {

int i=0,err;
pthread_t tid[NUM];
void *tret;
for(;i<NUM;i++)
{
err=pthread_create(&tid[i],NULL,thread_func,(void *)i);
if(err!=0)
{
printf("thread_create error:%s\n",strerror(err));
exit(-1);
}
}
for (i = 0; i < NUM; i++)
{
err = pthread_join(tid[i], &tret);
if (err != 0)
{
printf("can not join with thread %d:%s\n", i,strerror(err));
exit(-1);
}
}
printf("\n");
return 0;
}