Getting the Thread ID In C

As we have see in the pthread_self(),the ID is implemented or maintained by threading implementation not by the kernel,so for getting the unique ID assiged by the kernel we have to use the system call...

Take a look at the example...

#include<stdio.h>
#include<stdlib.h>
#include<pthread.h>
#include<linux/unistd.h>
#include<sys/syscall.h>
void* printid(void *ptr)
{
printf("The id of %s is %u\n",(char*)ptr,syscall( __NR_gettid ));
}
int main()
{
    pthread_t thread[5];
    char *msg[]={"thread1","thread2","thread3","thread4","thread5"};
    int i;
    for(i=0;i<5;i++)
    {
        pthread_create(&thread[i],NULL,printid,(void*)msg[i]);
        pthread_join(thread[i],NULL);
    }
    return 0;
}

output:

On my system the output is:

The id of thread1 is 18622

The id of thread2 is 18623

The id of thread3 is 18624

The id of thread4 is 18625

The id of thread5 is 18626

As you can see now the IDs are different because they are assigned by the kernel not by the threading implementation...

Also look at :gettid() vs pthread_self()