why use thread in linux print same pid?

Question

I am reading a book about unix .It said in linux , thread has different pid . And give the code below to print pid and thread id. I use SUSE and gcc.However, I get the same pid.Can anyone tell me why? Thanks.

#include "pthread.h"
pthread_t ntid;

void printids(const char *s)
{
    pid_t pid;
    pthread_t   tid;
    pid = getpid();
    tid = pthread_self();
    printf("%s pid = %u tid = %u  (0x%x)\n",s,(unsigned int)pid,(unsigned int)tid,(unsigned int)tid);
}
void *thr_fn(void *arg)
{
    printids("new thread :");
    return (void *)0;
}
int main()
{
    int err;
    err = pthread_create(&ntid,NULL,thr_fn,strerror(err));
    if(err != 0)
        err_quit("can't create new thread :%s\n",strerror(err));
    printids("main thread :");
    sleep(1);
    exit(0);
}

But,I get this:

main thread : pid = 2945 tid = 3075803392  (0xb7550900)
new thread : pid = 2945 tid = 3075799872  (0xb754fb40)

There must be an error in the book or you haven't read it properly. — piokuc, Aug 02 '13 at 13:45
You can find a nice explanation in the answers to this question: http://stackoverflow.com/questions/9305992/linux-threads-and-process — LostBoy, Aug 02 '13 at 13:47
Thread implementations changed inside Linux (from X.Leroy's original threads to NPTL today), and the changes interacted with kernel changes. — Basile Starynkevitch, Aug 02 '13 at 13:57
@piokuc The book is Stevens《Advanced Programming in UNIX Environment》. Is it old now? — Lidong Guo, Aug 02 '13 at 14:01
Yes, it is an old book, but very good for the general Posix part. Linux specific parts could be less actual. — Basile Starynkevitch, Aug 02 '13 at 14:02

score 2 · Accepted Answer · edited May 23 '17 at 11:47

2

In Linux threads have the same thread when viewed from user space, from a view space they each have a separate PID.

See also: Linux - Threads and Process

edited May 23 '17 at 11:47

Community

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answered Aug 02 '13 at 13:47

LostBoy

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score 0 · Answer 2 · answered Aug 02 '13 at 13:45

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Threads are a concept in the same process, they always have the same pid. The pid only changes if you fork a process; in this case, the child process will have a different pid than the parent.

answered Aug 02 '13 at 13:45

Femaref

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But the book said :linux use clone to create new thread .which means different pid. – Lidong Guo Aug 02 '13 at 13:48

why use thread in linux print same pid?

2 Answers2