Re: same pid ?

[ratheesh k <ratheesh.ksz@gmail.com>]

Just to summarize .....

All processes in a thread group (i.e., different execution contexts of
a process created by calling  clone with CLONE_THREAD as we will see
below) have a uniform thread group id (TGID). If a  process does not
use threads, its PID and TGID are identical.

getpid() returns tgid in pthread implementation. we have uniquid tid
for each thread, this could be returned using gettid().

-Ratheesh

2011/2/11 ratheesh k <ratheesh.ksz@gmail.com>:
> 2011/2/11 Steve Graegert (スティーブ) <graegerts@gmail.com>:
>> POSIX.1 requires threads to share a couple of attributes (mainly
>> process attributes) like the process ID, open FDs and many others.
>> What you are referring to ("everything as task") is the fact that each
>> thread is associated with a single scheduling entity within the kernel
>> implementing a 1:1 mapping.  Yet, threads created within the same
>> process share a single PID.
>>
>
> Thanks steve.
>
> I found some more info. posix thread uses CLONE_THREAD with clone()
> system call.
> i quoted from - man clone
>
> CLONE_THREAD (since Linux 2.4.0-test8)
>    If CLONE_THREAD is set, the child is placed in the same thread
> group as the calling process. To make the remainder of the discussion
> of CLONE_THREAD more readable, the term "thread" is used to refer to
> the processes within a thread group.
>
>    Thread groups were a feature added in Linux 2.4 to support the
> POSIX threads notion of a set of threads that share a single PID.
> Internally, this shared PID is the so-called thread group identifier
> (TGID) for the thread group. Since Linux 2.4, calls to getpid(2)
> return the TGID of the caller.
>
> -Ratheesh
>
>
>
>> On Fri, Feb 11, 2011 at 03:18, ratheesh k <ratheesh.ksz@gmail.com> wrote:
>>>>On Fri, Feb 11, 2011 at 4:56 AM, Jonathan Isom <jeisom@gmail.com> wrote:
>>>> Newer distros use Native POSIX Thread Library (NPTL).  They return the same pid.
>>>
>>> if linux treats every thing as task (both thread and process ) and
>>> CLONE_PID flag is obsolete, i expected unique pid.
>>
>
>> You are advised to consult pthreads(7) to make yourself familiar with the topic.
>>
>> Steve
>>
>