LinuxQuestions.org - Which function returns LWP in Linux.

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Which function returns LWP in Linux.

Hi,

For a process, we have different PIDs. For threads under a single processes, we have different LWP id, but same PID in Linux.
ex.

Code:

root@pc:/home/srinivas# ps -eLf

UID        PID  PPID    LWP  C STIME      TIME    CMD

root      100    1    100  0 May13      00:00:02 ./a.out

root      100    1    102  0 May13      00:00:00 ./a.out

getpid() function returns PID of a process.
Which function retuns LWP id for thread?

Sincerely,
Srinivas Nayak

Try gettid (get thread ID) -- I think it's what you're looking for.

Code:

#include<stdio.h>

#include <unistd.h>

#include <sys/syscall.h>

#include <sys/types.h>

#include<pthread.h>



#define NUM_THREADS    5



void *PrintLWPid(void *threadid)

{

  long tid;

  tid = (long)threadid;



  printf("It's me, thread %ld and my LWP id=%ld!\n", tid, syscall(SYS_gettid));

  sleep(60);

  pthread_exit(NULL);

}



int main (int argc, char *argv[])

{

  pthread_t threads[NUM_THREADS];

  int rc;

  long t;

  for(t=0; t<NUM_THREADS; t++){

      printf("In main: creating thread %ld\n", t);

      rc = pthread_create(&threads[t], NULL, PrintLWPid, (void *)t);

      if (rc){

        printf("ERROR; return code from pthread_create() is %d\n", rc);

        return -1;

      }

  }

  sleep(60);

  pthread_exit(NULL);

}

Note SYS_gettid is actually merely a define to __NR_gettid.