gettid 和pthread_self的区别

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gettid 和pthread_self的区别
The man page for gettid says:
The thread ID returned by this call is not the same thing as a POSIX thread ID
(i.e., the opaque value returned by pthread_self(3)).
看来，线程的id，在linux中分为POSIX thread ID , 和内核中对每一个线程的id.
gettid是linux 的一个系统调用， 查看sys_gettid
/* Thread ID - the internal kernel "pid" */
asmlinkage long sys_gettid(void)
{
    return task_pid_vnr(current);
}
struct upid {
    /* Try to keep pid_chain in the same cacheline as nr for find_pid */
    int nr;
    struct pid_namespace *ns;
    struct hlist_node pid_chain;
};
struct pid
{
    atomic_t count;
    /* lists of tasks that use this pid */
    struct hlist_head tasks[PIDTYPE_MAX];
    struct rcu_head rcu;
    int level;
    struct upid numbers[1];
};
这里面的level不清楚是什么含义？ 有知道的告诉我，多谢了。
问：_syscall[0-6]跑哪里去了
答：没有了
问：那现在用啥呢？
答：用系统调用 syscall(2)，第一个参数是SYS_name，后面参数照写
#define _GNU_SOURCE
#include stdio.h>
#include sys/types.h>
#include pthread.h>
#include stdlib.h>
#include string.h>
#include unistd.h>
#include linux/unistd.h>
#include sys/syscall.h>
void *thsf(void *arg)
{
    pthread_t th;
    char *retstr;
    retstr=malloc(50);
    memset(retstr,0,50);
    strcpy(retstr,"New thread quit!");
    th=pthread_self();
#if 1
    printf("New thread,pid:%d,tid:%x,another tid:%x.\n",
                      getpid(),
                      th,
                      (long)syscall(SYS_gettid));
#endif
   
    pthread_exit(retstr);
}
int main()
{
        pthread_t nth1,mth,oth;
        void *a;
        if(<span style="color: rgb(255, 0, 0);"%

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