linux开发---14.【C】线程的创建结束与锁

一. 线程
1. 基本函数
a. 关于pthread_id

/usr/include/x86_64-linux-gnu/bits/pthreadtypes.h:
typedef unsigned long int pthread_t;

定义为unsigned long int,这样打印时就可以用%u来打印了
b. 线程创建函数
线程函数都在:/usr/include/pthread.h中

extern int pthread_create (pthread_t *__restrict __newthread,
               const pthread_attr_t *__restrict __attr,
               void *(*__start_routine) (void *),
               void *__restrict __arg) __THROWNL __nonnull ((1, 3));

arg1: 值传递,获取了新创建的线程id
arg2: 线程的属性
arg3: 线程回调函数
arg4: 回调函数的参数
c.进程等侍线程结束

extern int pthread_join (pthread_t __th, void **__thread_return);

线程是依赖于进程存在的，一旦进制结束就没线程什么事了。
为了防止进制结束时，还有线程要执行,需要等侍线程结束
这个等侍函数就是pthread_join
d. 获取线程id

extern pthread_t pthread_self (void) __THROW __attribute__ ((__const__));

注意:只有在线性的回调函数中调用才可以获取id,在main函数中是main的thread_id
2. 创建线程
2.1.1 创建线程不带参数

cong@msi:/work/test/thread/1start$ cat start.c
#include "utils.h"

void* thread_routine(void* arg)
{
    dbmsg("%u",(unsigned int)pthread_self());
    return NULL;
}
int main ( int argc, char *argv[] )
{
    pthread_t thread_id;
    void* thread_result;
    int status;
    //创建线程: 无属性设置,回调是thread_routine,无参数
    status = pthread_create(&thread_id, NULL, thread_routine, NULL);
    if(status != 0)
    {
         dbmsg("%s",strerror(errno));
         return -1;
    }
    dbmsg("%u", (unsigned int)thread_id);

    status = pthread_join(thread_id, &thread_result);    //等侍线程执行结束
    if( status != 0)
    {
        dbmsg("%s", strerror(errno));
        return -1;
    }

    if(thread_result == NULL)
        return 0;
    return EXIT_SUCCESS;
}

1start.rar (下载后改名为1start.rar)
2.1.2 创建线程带参数

cong@msi:/work/test/thread/1start$ cat start.c
#include "utils.h"

void* thread_routine(void* arg)
{
    printf("%s", (char*) arg);  //打印参数
    return NULL;
}

int main ( int argc, char *argv[] )
{
    pthread_t thread_id;
    char buf[1024]= "hello,world\n";
    //创建线程: 将buf用为参数
    pthread_create(&thread_id, NULL, thread_routine, (void*)buf);

    pthread_join(thread_id, NULL);

    return EXIT_SUCCESS;
}

cong@msi:/work/test/thread/1start$ ./start
hello,world
2.2 线程退出

cong@msi:/work/test/thread/2exit$ cat exit.c
#include "utils.h"

void* thread_routine(void* arg)
{
    dbmsg("%u",(unsigned int)pthread_self());
    return ((void*)2);   //将线程结束值返回
}

int main ( int argc, char *argv[] )
{
    pthread_t thread_id;
    void* thread_result;
    int status;
    //创建线程: 无属性设置,回调是thread_routine,无参数
    status = pthread_create(&thread_id, NULL, thread_routine, NULL);

    status = pthread_join(thread_id, &thread_result);   //等侍线程结束，结束时返回值放在thread_result中

    dbmsg("thread exit code=%d", (int)thread_result);   //打印看一下

    return EXIT_SUCCESS;
}

cong@msi:/work/test/thread/2exit$ ./exit
exit.c:main[19]: thread exit code=2     -->就是这个 
2exit.rar  (下载后改名为3mutex.tar.gz)
2.3 锁
a.不明显但不等于不存在
两个线程同时访问一个数据时，要加锁

cong@msi:/work/test/thread/3mutex$ cat mutex.c
#include "utils.h"
int globle;                             //要保护的全局变量
pthread_mutex_t thread_mutex;

void* thread_routine(void* arg)
{
    pthread_mutex_lock(&thread_mutex);      //2.上锁
    globle ++;                              //把要保护的数据放中间
    dbmsg("globle=%d",globle);
    pthread_mutex_unlock(&thread_mutex);    //3.解锁
    return ((void*)2);
}

int main ( int argc, char *argv[] )
{
    pthread_t thread_id1;
    pthread_t thread_id2;
    void* thread_result;
    int status;

    globle = 1;
    pthread_mutex_init(&thread_mutex, NULL);     //1.初始化锁

    status = pthread_create(&thread_id1, NULL, thread_routine, NULL);
    status = pthread_create(&thread_id2, NULL, thread_routine, NULL);

    status = pthread_join(thread_id1, &thread_result);
    status = pthread_join(thread_id2, &thread_result);

    return EXIT_SUCCESS;
}

结果:
cong@msi:/work/test/thread/3mutex$ ./mutex
mutex.c:thread_routine[9]: globle=2
mutex.c:thread_routine[9]: globle=3
b.来个明显的
b.1 第1个线程运行时，在回调函数中产生一个局部变量buf_1指向参数buf1的首地址，
获取锁，进行打印
b.2 此时第2个线程开始运行，在回调函数中产生一个局部变量buf_2指向参数buf1的首地址，
获取不了锁，不能进行打印，一直在等侍线程1运行结束释放锁
b.3然后线程2开始打印
b.4 如果没有锁时，就会出乱子

cong@msi:/work/test/thread/3mutex$ cat ./mutex.c
#include "utils.h"
pthread_mutex_t thread_mutex;

void* thread_routine(void* arg)
{
    char* buf = (char*) arg;
    //pthread_mutex_lock(&thread_mutex);     //加上锁之后就不存在问题了
    while(*buf != '\0')
    {
        printf("%c", *buf);
        buf++;
    }
    printf("\n");
    //pthread_mutex_unlock(&thread_mutex);
    return NULL;
}

int main ( int argc, char *argv[] )
{
    pthread_t thread_id1;
    pthread_t thread_id2;
    void* thread_result;
    int status;
    int i;
    char buf1[1024];
    char buf2[1024];
    for(i=0;i<1023; i++)
    {
        buf1[i] = 'a';
        buf2[i] = 'b';
    }
    buf1[1023] = '\0';
    buf2[1023] = '\0';


    pthread_mutex_init(&thread_mutex, NULL);

    status = pthread_create(&thread_id1, NULL, thread_routine, (void*)buf1);
    status = pthread_create(&thread_id2, NULL, thread_routine, (void*)buf2);

    status = pthread_join(thread_id1, &thread_result);
    status = pthread_join(thread_id2, &thread_result);

    return EXIT_SUCCESS;
}

结果:

cong@msi:/work/test/thread/3mutex$ ./mutex   -->第1次执行没有出现问题
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cong@msi:/work/test/thread/3mutex$ ./mutex  -->第2次执行发现出问题了，这跟等公交车一样，不等车时一个接一个的车来了，真要等车时车反而不来了
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3mutex.rar (下载后改名为3mutex.tar.gz)