From mboxrd@z Thu Jan  1 00:00:00 1970
From: dhylands@gmail.com (Dave Hylands)
Date: Wed, 29 Dec 2010 15:30:55 -0800
Subject: Can I get thread ID in user-mode program?
In-Reply-To: <AANLkTinPkaX_4fn-CeQccdZBgyHa_hBC-G9zqTkChnhn@mail.gmail.com>
References: <AANLkTinPkaX_4fn-CeQccdZBgyHa_hBC-G9zqTkChnhn@mail.gmail.com>
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To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

Hi,

On Wed, Dec 29, 2010 at 9:30 AM, CP YEH <ntdev74@gmail.com> wrote:
> Hi,
>
> I would like to know if I can obtain thread id of calling thread. Let
> me clarify what I mean by this.
>
> First, here is task_struct from linux kernel code.
>
> struct task_struct {
> ? ? ? struct list_head tasks;
> ? ? ? pid_t pid;
> ? ? ? pid_t tgid;
> ? ? ? struct task_struct *group_leader; ?/* threadgroup leader */
> ? ? ? struct list_head thread_group;
> };
>
> I understand that getpid returns tgid and gettid via __NR_gettid
> returns tid but according to manpage, it seems to me that it is same
> as what I get from getpid().
>
> Man page of gettid:
> ? ? ? gettid() returns the thread ID of the current process. ?This is
> equal to the
> ? ? ? process ID (as returned by getpid(2)), unless ?the ?process ?is
> ?part ?of ?a
> ? ? ? thread ?group
>
> However, I would like to obtain pid of task_struct. Is there any way I
> can get that information?

>>From my understanding, this sort of depends on which threading model
is being employed.

For standard distros (like ubuntu), I believe that getpid returns the
tgid, and gettid (aka syscall( 224 )) returns pid of the task struct
(which is really a thread id).

Dave Hylands