Can I get thread ID in user-mode program?

[Dave Hylands]

Hi,

On Wed, Dec 29, 2010 at 9:30 AM, CP YEH <ntdev74 at 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