多线程运用

1.使用三个线程完成两个文件的拷贝工作，线程1拷贝前一半，线程2拷贝后一半，主线程主要用于回收子线程的资源 

#include <head.h>
sem_t sem;
struct rw
{
	off_t size;
	int fr;
	int fw;
};
void *task1(void *arg)
{
	sem_wait(&sem);
	struct rw *l=(struct rw *)arg;
	lseek(l->fr,0,SEEK_SET);
	lseek(l->fw,0,SEEK_SET);
	char c=0;
	int i=0;
	while(i<=l->size/2)
	{
		read(l->fr,&c,sizeof(c));
		write(l->fw,&c,sizeof(c));
		i++;
	}
	printf("i1=%d\n",i);
	pthread_exit(NULL);
}
void *task2(void *arg)
{
	struct rw *l=(struct rw*)arg;
	lseek(l->fr,l->size/2,SEEK_SET);
	lseek(l->fw,l->size/2,SEEK_SET);
	int i=0;
	char c=0;
	while(i<l->size/2)
	{
		read(l->fr,&c,sizeof(c));
		write(l->fw,&c,sizeof(c));
		i++;
	}
	printf("i2=%d\n",i);
	sem_post(&sem);
	pthread_exit(NULL);
}
int main(int argc, const char *argv[])
{  
	int fr=open("./1.jpg",O_RDONLY);
	if(fr<0)
	{
		perror("open");
		return -1;
	}
	int fw=open("./2.jpg",O_WRONLY|O_CREAT|O_TRUNC,0777);
	if(fw<0)
	{
		perror("open");
		return -1;
	}
	off_t size=lseek(fr,0,SEEK_END);
	printf("size=%ld\n",size);
	struct rw arg;
	arg.size=size;
	arg.fr=fr;
	arg.fw=fw;
	sem_init(&sem,0,0);
	pthread_t tid1,tid2;
	if(pthread_create(&tid1,NULL,task1,&arg)!=0)
	{
		printf("tid1 create error\n");
		return -1;
	}
	if(pthread_create(&tid2,NULL,task2,&arg)!=0)
	{
		printf("tid2 create error\n");
		return -1;
	}
	pthread_join(tid1,NULL);
	pthread_join(tid2,NULL);
	sem_destroy(&sem);
	if(close(fr)<0)
	{
		perror("close");
		return -1;
	}
	if(close(fw)<0)
	{
		perror("close");
		return -1;
	}
	return 0;
} 

 2.使用三个线程完成，第一个线程输出A，第二个线程输出B，第三个线程输出C，最终输出的结果为：ABCABCABCABCABC

#include <head.h>
sem_t sem1,sem2;
void *task3(void *arg)
{
	int num=5;
	while(num--)
	{
		sem_wait(&sem2);
		printf("C");
		}
pthread_exit(NULL);
}
void *task1(void *arg)
{
	int num=5;
	while(num--)
	{
		sleep(1);
		sem_wait(&sem1);
		printf("B");
		sem_post(&sem2);
	}
	pthread_exit(NULL);
}
void *task2(void *arg)
{
	int num=5;
	while(num--)
	{
		sleep(2);
		printf("A");
		sem_post(&sem1);
	}
	pthread_exit(NULL);
}
int main(int argc, const char *argv[])
{
	sem_init(&sem1,0,0);
	sem_init(&sem2,0,0);
	pthread_t tid1,tid2,tid3;
	if(pthread_create(&tid1,NULL,task1,NULL)!=0)
	{
		printf("tid1 create error\n");
		return -1;
	}
	if(pthread_create(&tid2,NULL,task2,NULL)!=0)
	{
		printf("tid2 create error\n");
		return -1;
	}
	if(pthread_create(&tid3,NULL,task3,NULL)!=0)
	{
		printf("tid3 create error\n");
		return -1;
	}
	pthread_join(tid1,NULL);
	pthread_join(tid2,NULL);
	pthread_join(tid3,NULL);
	sem_destroy(&sem1);
	sem_destroy(&sem2);

	return 0;
}