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
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
#include
#include
#include
#include
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
#include
#include
#include
#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
#include
#include
#include
#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
#include
#include
#include
#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
#include
#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;
}