How to get the pid of thread?

U are referring to kernel right?

It is in fs/proc/base.c: proc_task_read() function (which is called when u try to read the directory /proc/xxxx/task):

Following function is shown:

/* f_version caches the tgid value that the last readdir call couldn't * return. lseek aka telldir automagically resets f_version to

1. */ ns = filp->f_dentry->d_sb->s_fs_info; tid = (int)filp->f_version; filp->f_version = 0; for (task = first_tid(leader, tid, pos - 2, ns); task; task = next_tid(task), pos++) { tid = task_pid_nr_ns(task, ns); if (proc_task_fill_cache(filp, dirent, filldir, task, tid) < 0) { /* returning this tgid failed, save it as the first * pid for the next readir call */ filp->f_version = (u64)tid; put_task_struct(task); break; } } out:

The above for-loop will print out all the thread ID of the particular process, eg:

ls /proc/3407/task/