what's the relationship between tgid, tid and pid ?

From: Hu, Boris (boris.hu@intel.com)
Date: Thu Dec 05 2002 - 14:36:21 EST


Linux 2.5.49
NTPL 0.10

I learned from the kernel source. sys_getpid() returns tgid and
sys_gettid() returns pid. Moreover,
/kernel/source/fork.c
copy_process()
771 if (clone_flags & CLONE_PARENT_SETTID)
772 if (put_user(p->pid, parent_tidptr)) // parent_tidptr is tid in struct
pthread
                                   ....
It seems tid = pid, while tgid is head pthread pid.

But the following lines let me confused.
/kernel/source/fork.c
copy_process()
893 p->tgid = p->pid;
894 p->group_leader = p;
every pthread_create()->sys_clone()->do_fork()->copy_process()
p->tgid will be overwritten every time?

any comments? thanks.

  Boris
=========================
To know what I don't know
To learn what I don't know
To contribute what I know
=========================

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