linux c編程 多線程（初級）

進程簡單的說就是把一段代碼複製成多份，並讓他們同時執行。進程間通訊是爲了讓他們有序的運行

線程簡單的說就是讓多個函數同時執行，線程間通訊是爲了讓他們有序的運行

編譯線程程序時會警告說線程函數找不到

 pthread 庫不是 Linux 系統默認的庫，鏈接時須要使用靜態庫 libpthread.a，因此在使用pthread_create()建立線程，以及調用 pthread_atfork()函數創建fork處理程序時，須要連接該庫。

問題解決：
    在編譯中要加 -lpthread參數
    gcc thread.c -o thread -lpthread
    thread.c爲你些的源文件，不要忘了加上頭文件#include<pthread.h>

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

實例1：建立兩個線程，同時執行同一個函數

/* 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);
}

 

執行gcc ex7-1.c -lpthread

./a.out

 

實例2  建立多個線程執行不一樣函數

代碼來自 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 :主函數在等我完成任務嗎？\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 :主函數在等我完成任務嗎？\n");
    pthread_exit(NULL);
}
 
 
void thread_create(void)
{
    int temp;
    memset(&thread, 0, sizeof(thread)); //comment1
    //建立線程
    if((temp = pthread_create(&thread[0], NULL, thread1, NULL)) != 0) //comment2
        printf("線程1建立失敗!\n");
    else
        printf("線程1被建立\n");
    if((temp = pthread_create(&thread[1], NULL, thread2, NULL)) != 0) //comment3
        printf("線程2建立失敗");
    else
        printf("線程2被建立\n");
}
 
void thread_wait(void)
{
    //等待線程結束
    if(thread[0] !=0) { //comment4
        pthread_join(thread[0],NULL);
        printf("線程1已經結束\n");
    }
    if(thread[1] !=0) { //comment5
        pthread_join(thread[1],NULL);
        printf("線程2已經結束\n");
    }
}
 
int main()
{
    //用默認屬性初始化互斥鎖
    pthread_mutex_init(&mut,NULL);
    printf("我是主函數哦，我正在建立線程，呵呵\n");
    thread_create();
    printf("我是主函數哦，我正在等待線程完成任務阿，呵呵\n");
    thread_wait();
    return 0;
}

 

?

編譯 :

       gcc -lpthread -o thread_example lp.c

 

 

實例3：信號量控制線程運行順序

/* 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;        
}

 

實例4：互斥鎖的使用

 

在這個程序中，一個線程要往緩衝區寫數據，另外一個線程要讀數據，每次只能讓一個線程操做緩衝區

/*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);
}
}

實例5 條件變量

text

 

[cpp] view plain copy

 print?

1. /* ex7-4.c */  
2. #include <stdio.h>  
3. #include <pthread.h>  
4. #define BUFFER_SIZE 4  
5. #define OVER (-1)  
6. struct producers  
7. {  
8.     int buffer[BUFFER_SIZE];  
9.     pthread_mutex_t lock;  
10.     int     readpos, writepos;  
11.     pthread_cond_t  notempty;  
12.     pthread_cond_t  notfull;  
13. };  
14.   
15. void init(struct producers *b)  
16. {  
17.     pthread_mutex_init(&b->lock,NULL);  
18.     pthread_cond_init(&b->notempty,NULL);  
19.     pthread_cond_init(&b->notfull,NULL);  
20.     b->readpos=0;  
21.     b->writepos=0;  
22. }  
23.   
24. void put(struct producers *b, int data)  
25. {  
26.     pthread_mutex_lock(&b->lock);  
27.     while((b->writepos+1)%BUFFER_SIZE==b->readpos)  
28.     {  
29.         pthread_cond_wait(&b->notfull,&b->lock);  
30.     }  
31.   
32.     b->buffer[b->writepos]=data;  
33.     b->writepos++;  
34.     if(b->writepos>=BUFFER_SIZE) b->writepos=0;  
35.     pthread_cond_signal(&b->notempty);  
36.     pthread_mutex_unlock(&b->lock);  
37. }  
38.   
39. int get(struct producers *b)  
40. {  
41.     int data;  
42.     pthread_mutex_lock(&b->lock);  
43.     while(b->writepos==b->readpos)  
44.     {  
45.         pthread_cond_wait(&b->notempty,&b->lock);  
46.     }  
47.     data=b->buffer[b->readpos];  
48.     b->readpos++;  
49.     if(b->readpos>=BUFFER_SIZE) b->readpos=0;  
50.     pthread_cond_signal(&b->notfull);  
51.     pthread_mutex_unlock(&b->lock);  
52.     return data;  
53. }  
54.   
55. struct producers  buffer;  
56. void *producer(void *data)  
57. {  
58.     int n;  
59.     for(n=0;n<10;n++)  
60.     {  
61.         printf("Producer : %d-->\n",n);  
62.         put(&buffer,n);  
63.     }  
64.     put(&buffer,OVER);  
65.     return NULL;  
66. }  
67.   
68. void *consumer(void *data)  
69. {  
70.     int d;  
71.     while(1)  
72.     {  
73.         d=get(&buffer);  
74.         if(d==OVER) break;  
75.         printf("Consumer: --> %d\n",d);  
76.     }  
77.     return NULL;  
78. }  
79.   
80. int main()  
81. {  
82.     pthread_t tha,thb;  
83.     void *retval;  
84.     init(&buffer);  
85.     pthread_create(&tha,NULL,producer,0);  
86.     pthread_create(&thb,NULL,consumer,0);  
87.     pthread_join(tha,&retval);  
88.     pthread_join(thb,&retval);  
89.     return 0;  
90.   
91. }