线程的创建，pthread_create，pthread_self，pthread_once

typedef unsigned long int pthread_t;

//come from /usr/include/bits/pthreadtypes.h

int pthread_create(pthread_t *thread, const pthread_attr_t *attr,void *(*start_routine) (void *), void *arg);创建新的线程

pthread_t pthread_self(void);获取本线程的线程ID

int pthread_equal(pthread_t t1, pthread_t t2);判断两个线程ID是否指向同一线程

int pthread_once(pthread_once_t *once_control, void (*init_routine) (void))；用来保证init_routine线程函数在进程中只执行一次。

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



int* thread_func(void* arg)
{
    pthread_t new_thid;
    new_thid = pthread_self();//打印线程自己的线程ID
    printf("the new thread, ID is %lu
", new_thid);

    return NULL;
}


int main()
{
    pthread_t thid;

    printf("main thread, ID is %lu
", pthread_self());//打印主线程自己的线程ID

    if (pthread_create(&thid, NULL, (void*)thread_func, NULL) != 0)
    {
        printf("create thread failed
");
        exit(0);
    }

    
    sleep(5);

    return 0;
}

某些情况下，函数执行次数要被限制为1次，这种情况下，要使用pthread_once，代码示例：

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


pthread_once_t once = PTHREAD_ONCE_INIT;

void run(void)
{
    printf("function run is running in thread:%lu
", pthread_self());
}


int* thread1(void* arg)
{
    pthread_t new_thid;
    new_thid = pthread_self();
    printf("current thread ID is %lu
", new_thid);
    pthread_once(&once, run);
    printf("thread1 end
");
    return NULL;
}

int* thread2(void* arg)
{
    pthread_t new_thid;
    new_thid = pthread_self();
    printf("current thread ID is %lu
", new_thid);
    pthread_once(&once, run);
    printf("thread2 end
");
    return NULL;
}

int main()
{
    pthread_t thid1, thid2;

    printf("main thread, ID is %lu
", pthread_self());

    pthread_create(&thid1, NULL, (void*)thread1, NULL);
    pthread_create(&thid2, NULL, (void*)thread2, NULL);
    
    sleep(5);    
    printf("main thread exit
");

    return 0;
}

运行结果：

main thread, ID is 3076200128
current thread ID is 3067804480
function run is running in thread:3067804480
thread2 end
current thread ID is 3076197184
thread1 end
main thread exit

虽然在thread1 跟thread2中都调用了run函数，但是run函数只执行了一次。