same pid ?

same pid ?

[ratheesh k]

i created two threads with pthread library. But both threads returns
same pid with getpid() function. ???


-Ratheesh

Re: same pid ?

[Michal Nazarewicz]

On Thu, 10 Feb 2011 12:37:25 +0100, ratheesh k <ratheesh.ksz@gmail.com>  
wrote:
> i created two threads with pthread library. But both threads returns
> same pid with getpid() function. ???

PID is a Process ID.  All threads in given process have the same PID.

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Re: same pid ?

[ratheesh k]

2011/2/10 Michal Nazarewicz <mina86@mina86.com>:
> On Thu, 10 Feb 2011 12:37:25 +0100, ratheesh k <ratheesh.ksz@gmail.com>
> wrote:
>>
>> i created two threads with pthread library. But both threads returns
>> same pid with getpid() function. ???
>
> PID is a Process ID.  All threads in given process have the same PID.
>

pthread uses clone system call. doen't it ? if so, please see - man clone


 CLONE_PID (obsolete)
             If  CLONE_PID is set, the child process is created with the same
             process ID as the calling process.  This is good for hacking the
             system,  but  otherwise of not much use.  Since 2.3.21 this flag
             can be specified only by the system boot process  (PID  0).   It
             disappeared in Linux 2.5.16.








> --
> Best regards,                                       _     _
> .o. | Liege of Serenly Enlightened Majesty of     o' \,=./ `o
> ..o | Computer Science,  Michal "mina86" Nazarewicz  (o o)
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Re: same pid ?

[Jonathan Isom]

On Thu, Feb 10, 2011 at 12:09 PM, ratheesh k <ratheesh.ksz@gmail.com> wrote:
> 2011/2/10 Michal Nazarewicz <mina86@mina86.com>:
>> On Thu, 10 Feb 2011 12:37:25 +0100, ratheesh k <ratheesh.ksz@gmail.com>
>> wrote:
>>>
>>> i created two threads with pthread library. But both threads returns
>>> same pid with getpid() function. ???
>>
>> PID is a Process ID.  All threads in given process have the same PID.
>>
>
> pthread uses clone system call. doen't it ? if so, please see - man clone
>
>
>  CLONE_PID (obsolete)
>             If  CLONE_PID is set, the child process is created with the same
>             process ID as the calling process.  This is good for hacking the
>             system,  but  otherwise of not much use.  Since 2.3.21 this flag
>             can be specified only by the system boot process  (PID  0).   It
>             disappeared in Linux 2.5.16.
>
>

Newer distros use Native POSIX Thread Library (NPTL).  They return the same pid.


>
>
>
>
>
>> --
>> Best regards,                                       _     _
>> .o. | Liege of Serenly Enlightened Majesty of     o' \,=./ `o
>> ..o | Computer Science,  Michal "mina86" Nazarewicz  (o o)
>> ooo +-<email/jid: mnazarewicz@google.com>--------ooO--(_)--Ooo--
>>
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>



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Re: same pid ?

[ratheesh k]

>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.

-ratheesh



On Fri, Feb 11, 2011 at 4:56 AM, Jonathan Isom <jeisom@gmail.com> wrote:
> On Thu, Feb 10, 2011 at 12:09 PM, ratheesh k <ratheesh.ksz@gmail.com> wrote:
>> 2011/2/10 Michal Nazarewicz <mina86@mina86.com>:
>>> On Thu, 10 Feb 2011 12:37:25 +0100, ratheesh k <ratheesh.ksz@gmail.com>
>>> wrote:
>>>>
>>>> i created two threads with pthread library. But both threads returns
>>>> same pid with getpid() function. ???
>>>
>>> PID is a Process ID.  All threads in given process have the same PID.
>>>
>>
>> pthread uses clone system call. doen't it ? if so, please see - man clone
>>
>>
>>  CLONE_PID (obsolete)
>>             If  CLONE_PID is set, the child process is created with the same
>>             process ID as the calling process.  This is good for hacking the
>>             system,  but  otherwise of not much use.  Since 2.3.21 this flag
>>             can be specified only by the system boot process  (PID  0).   It
>>             disappeared in Linux 2.5.16.
>>
>>
>
> Newer distros use Native POSIX Thread Library (NPTL).  They return the same pid.
>
>
>>
>>
>>
>>
>>
>>> --
>>> Best regards,                                       _     _
>>> .o. | Liege of Serenly Enlightened Majesty of     o' \,=./ `o
>>> ..o | Computer Science,  Michal "mina86" Nazarewicz  (o o)
>>> ooo +-<email/jid: mnazarewicz@google.com>--------ooO--(_)--Ooo--
>>>
>> --
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>> the body of a message to majordomo@vger.kernel.org
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>>
>
>
>
> --
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> Athlon II X4 640 Processor
> 4 Gigabytes of DDR2-800
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> KWorld ATSC 115 TV Capture Card
>
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Re: same pid ?

[Steve Graegert (スティーブ)]

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.

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.

You are advised to consult pthreads(7) to make yourself familiar with the topic.

Steve
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Re: same pid ?

[ratheesh k]

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
>

Re: same pid ?

[ratheesh k]

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
>>
>