linux c编程 多线程（初级）

进程简单的说就是把一段代码复制成多份，并让他们同时执行。进程间通信是为了让他们有序的运行

线程简单的说就是让多个函数同时执行，线程间通信是为了让他们有序的运行

编译线程程序时会警告说线程函数找不到

 pthread 库不是 Linux 系统默认的库，连接时需要使用静态库 libpthread.a，所以在使用pthread_create()创建线程，以及调用 pthread_atfork()函数建立fork处理程序时，需要链接该库。

问题解决：
    在编译中要加 -lpthread参数
    gcc thread.c -o thread -lpthread
    thread.c为你些的源文件，不要忘了加上头文件#include<pthread.h>

http://blog.csdn.net/llqkk/article/details/2854558

实例1：创建两个线程，同时执行同一个函数

/* ex7-1.c */
#include <stddef.h>
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <string.h>

void print_msg(char *ptr);

int main()
{
pthread_t thread1, thread2;
int i,j;
char *msg1="do sth1\n";
char *msg2="do sth2\n";
pthread_create(&thread1,NULL, (void *)(&print_msg), (void *)msg1);
pthread_create(&thread2,NULL, (void *)(&print_msg), (void *)msg2);
sleep(1);
return 0;
}

void  print_msg(char *ptr)
{
int retval;
int id=pthread_self();
printf("Thread ID: %x\n",id);
  printf("%s",ptr);
pthread_exit(&retval);
}

执行gcc ex7-1.c -lpthread

./a.out

实例2  创建多个线程执行不同函数

代码来自 http://www.cnblogs.com/BiffoLee/archive/2011/11/18/2254540.html

#include <pthread.h>
#include <stdio.h>
#include <sys/time.h>
#include <string.h>
#define MAX 10
 
pthread_t thread[2];
pthread_mutex_t mut;
int number=0, i;
 
void *thread1()
{
    printf ("thread1 : I'm thread 1\n");
    for (i = 0; i < MAX; i++)
        {
            printf("thread1 : number = %d\n",number);
            pthread_mutex_lock(&mut);
            number++;
            pthread_mutex_unlock(&mut);
            sleep(2);
        }
    printf("thread1 :主函数在等我完成任务吗？\n");
 
    pthread_exit(NULL);
 
}
 
void *thread2()
{
    printf("thread2 : I'm thread 2\n");
    for (i = 0; i < MAX; i++)
        {
            printf("thread2 : number = %d\n",number);
            pthread_mutex_lock(&mut);
            number++;
            pthread_mutex_unlock(&mut);
            sleep(3);
        }
    printf("thread2 :主函数在等我完成任务吗？\n");
    pthread_exit(NULL);
}
 
 
void thread_create(void)
{
    int temp;
    memset(&thread, 0, sizeof(thread)); //comment1
    //创建线程
    if((temp = pthread_create(&thread[0], NULL, thread1, NULL)) != 0) //comment2
        printf("线程1创建失败!\n");
    else
        printf("线程1被创建\n");
    if((temp = pthread_create(&thread[1], NULL, thread2, NULL)) != 0) //comment3
        printf("线程2创建失败");
    else
        printf("线程2被创建\n");
}
 
void thread_wait(void)
{
    //等待线程结束
    if(thread[0] !=0) { //comment4
        pthread_join(thread[0],NULL);
        printf("线程1已经结束\n");
    }
    if(thread[1] !=0) { //comment5
        pthread_join(thread[1],NULL);
        printf("线程2已经结束\n");
    }
}
 
int main()
{
    //用默认属性初始化互斥锁
    pthread_mutex_init(&mut,NULL);
    printf("我是主函数哦，我正在创建线程，呵呵\n");
    thread_create();
    printf("我是主函数哦，我正在等待线程完成任务阿，呵呵\n");
    thread_wait();
    return 0;
}

?

编译 :

       gcc -lpthread -o thread_example lp.c

实例3：信号量控制线程运行顺序

/* thread_sem.c */


#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>


#define THREAD_NUMBER 3
#define REPEAT_NUMBER 3
#define DELAY_TIME_LEVELS 10.0


sem_t sem[THREAD_NUMBER];


void * thrd_func(void *arg)
{
int thrd_num = (int)arg;
int delay_time = 0;
int count = 0;

sem_wait(&sem[thrd_num]);

printf("Thread %d is starting\n", thrd_num);

for (count = 0; count < REPEAT_NUMBER; count++)
{

delay_time = (int)(rand() * DELAY_TIME_LEVELS/(RAND_MAX)) + 1;
sleep(delay_time);
printf("\tThread %d: job %d delay = %d\n", thrd_num, count, delay_time);
}


printf("Thread %d finished\n", thrd_num);

pthread_exit(NULL);
}


int main(void)
{
pthread_t thread[THREAD_NUMBER];
int no = 0, res;
void * thrd_ret;

srand(time(NULL));

for (no = 0; no < THREAD_NUMBER; no++)
{
sem_init(&sem[no], 0, 0);
res = pthread_create(&thread[no], NULL, thrd_func, (void*)no);
if (res != 0)
{
printf("Create thread %d failed\n", no);
exit(res);
}
}

printf("Create treads success\n Waiting for threads to finish...\n");
sem_post(&sem[THREAD_NUMBER - 1]);
for (no = THREAD_NUMBER - 1; no >= 0; no--)
{
res = pthread_join(thread[no], &thrd_ret);
if (!res)
{
printf("Thread %d joined\n", no);
}
else
{
printf("Thread %d join failed\n", no);
}
sem_post(&sem[(no + THREAD_NUMBER - 1) % THREAD_NUMBER]);

}

for (no = 0; no < THREAD_NUMBER; no++)
{
sem_destroy(&sem[no]);
}


return 0;        
}

实例4：互斥锁的使用

在这个程序中，一个线程要往缓冲区写数据，另一个线程要读数据，每次只能让一个线程操作缓冲区

/*ex7-3.c*/


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


#define FALSE 0
#define TRUE 1


void readfun();
void writefun();


char buffer[256];
int buffer_has_item=0;
int retflag=FALSE,i=0;
pthread_mutex_t mutex;


int main()
{
void *retval;
pthread_t reader;
pthread_mutex_init(&mutex,NULL);
pthread_create(&reader,NULL,(void *)&readfun,NULL);
writefun();
pthread_join(reader,&retval);


}


void readfun()
{
while(1)
{
if(retflag)
return;
pthread_mutex_lock(&mutex);
if(buffer_has_item==1)
{
printf("%s",buffer);
buffer_has_item=0;
}
pthread_mutex_unlock(&mutex);
}
}
void writefun()
{
int i=0;
while(1)
{
if(i==10)
{
retflag=TRUE;
return;
}
pthread_mutex_lock(&mutex);
if(buffer_has_item==0)
{
sprintf(buffer,"This is %d\n",i++);
buffer_has_item=1;
}
pthread_mutex_unlock(&mutex);
}
}

实例5 条件变量

text

/* ex7-4.c */
#include <stdio.h>
#include <pthread.h>
#define BUFFER_SIZE 4
#define OVER (-1)
struct producers
{
	int buffer[BUFFER_SIZE];
	pthread_mutex_t	lock;
	int		readpos, writepos;
	pthread_cond_t	notempty;
	pthread_cond_t	notfull;
};

void init(struct producers *b)
{
	pthread_mutex_init(&b->lock,NULL);
	pthread_cond_init(&b->notempty,NULL);
	pthread_cond_init(&b->notfull,NULL);
	b->readpos=0;
	b->writepos=0;
}

void put(struct producers *b, int data)
{
	pthread_mutex_lock(&b->lock);
	while((b->writepos+1)%BUFFER_SIZE==b->readpos)
	{
		pthread_cond_wait(&b->notfull,&b->lock);
	}

	b->buffer[b->writepos]=data;
	b->writepos++;
	if(b->writepos>=BUFFER_SIZE) b->writepos=0;
	pthread_cond_signal(&b->notempty);
	pthread_mutex_unlock(&b->lock);
}

int get(struct producers *b)
{
	int data;
	pthread_mutex_lock(&b->lock);
	while(b->writepos==b->readpos)
	{
		pthread_cond_wait(&b->notempty,&b->lock);
	}
	data=b->buffer[b->readpos];
	b->readpos++;
	if(b->readpos>=BUFFER_SIZE) b->readpos=0;
	pthread_cond_signal(&b->notfull);
	pthread_mutex_unlock(&b->lock);
	return data;
}

struct producers  buffer;
void *producer(void *data)
{
	int n;
	for(n=0;n<10;n++)
	{
		printf("Producer : %d-->\n",n);
		put(&buffer,n);
	}
	put(&buffer,OVER);
	return NULL;
}

void *consumer(void *data)
{
	int d;
	while(1)
	{
		d=get(&buffer);
		if(d==OVER) break;
		printf("Consumer: --> %d\n",d);
	}
	return NULL;
}

int main()
{
	pthread_t tha,thb;
	void *retval;
	init(&buffer);
	pthread_create(&tha,NULL,producer,0);
	pthread_create(&thb,NULL,consumer,0);
	pthread_join(tha,&retval);
	pthread_join(thb,&retval);
	return 0;

}