Which function returns LWP in Linux.

Which function returns LWP in Linux.

[Srinivas Nayak]

Hi,

For a process, we have different PIDs. For threads under a single
processes, we have different LWP id, but same PID in Linux.
ex.

root@pc:/home/srinivas# ps -eLf
UID        PID  PPID     LWP  C STIME       TIME     CMD
root       100     1     100  0 May13       00:00:02 ./a.out
root       100     1     102  0 May13       00:00:00 ./a.out

getpid() function returns PID of a process.
Which function retuns LWP id for thread?

Sincerely,
Srinivas Nayak

Re: Which function returns LWP in Linux.

[Jaswinder Singh Rajput]

Hello,

On Mon, May 17, 2010 at 11:57 AM, Srinivas Nayak
<sinu.nayak2001@gmail.com> wrote:
> Hi,
>
> For a process, we have different PIDs. For threads under a single
> processes, we have different LWP id, but same PID in Linux.
> ex.
>
> root@pc:/home/srinivas# ps -eLf
> UID        PID  PPID     LWP  C STIME       TIME     CMD
> root       100     1     100  0 May13       00:00:02 ./a.out
> root       100     1     102  0 May13       00:00:00 ./a.out
>
> getpid() function returns PID of a process.
> Which function retuns LWP id for thread?
>

You are asking procps question in LKML.

Please check http://procps.sourceforge.net/

Download propps package, read source code and you will get the reply.

Thanks,
--
Jaswinder Singh.

Re: Which function returns LWP in Linux.

[KOSAKI Motohiro]

> Hi,
> 
> For a process, we have different PIDs. For threads under a single
> processes, we have different LWP id, but same PID in Linux.
> ex.
> 
> root@pc:/home/srinivas# ps -eLf
> UID        PID  PPID     LWP  C STIME       TIME     CMD
> root       100     1     100  0 May13       00:00:02 ./a.out
> root       100     1     102  0 May13       00:00:00 ./a.out
> 
> getpid() function returns PID of a process.
> Which function retuns LWP id for thread?

gettid()

Re: Which function returns LWP in Linux.

[Jaswinder Singh Rajput]

Hello KOSAKI-san,

On Mon, May 17, 2010 at 12:33 PM, KOSAKI Motohiro
<kosaki.motohiro@jp.fujitsu.com> wrote:
>> Hi,
>>
>> For a process, we have different PIDs. For threads under a single
>> processes, we have different LWP id, but same PID in Linux.
>> ex.
>>
>> root@pc:/home/srinivas# ps -eLf
>> UID        PID  PPID     LWP  C STIME       TIME     CMD
>> root       100     1     100  0 May13       00:00:02 ./a.out
>> root       100     1     102  0 May13       00:00:00 ./a.out
>>
>> getpid() function returns PID of a process.
>> Which function retuns LWP id for thread?
>
> gettid()
>

gettid() is linux specific and not supported in glibc. Normally
application do not use gettid(), even procps is not using it, that why
I suggested Srinivas to check procps source to find the best solution
for it.

Thanks,
--
Jaswinder Singh.

Re: Which function returns LWP in Linux.

[Srinivas Nayak]

>
> You are asking procps question in LKML.
>

Dear Jaswinder,

I am new to linux mailing lists. Thought, this process id related
question can only be answered by linux kernel developers, as they may be
working with this almost everyday. And more to this, I searched in the
Internet for LWP id, but found no positive answer. Many places gettid
was the answer, but it doesn't work.

I apologize, if lkml is not the best place to ask programming related
questions. It would be kind, if you let me know the correct mailing
list where general linux programming discussions happen. To my find,
linux-c-programming mailing list is not so active.

After some more research, i foind that

syscall(SYS_gettid)

returns LWP id. Isn't this correct?

Sincerely,
Srinivas Nayak

Re: Which function returns LWP in Linux.

[Samuel Thibault]

Srinivas Nayak, le Mon 17 May 2010 15:43:17 +0530, a écrit :
> After some more research, i foind that
> 
> syscall(SYS_gettid)
> 
> returns LWP id. Isn't this correct?

It is correct only on Linux, but yes.

Samuel

Re: Which function returns LWP in Linux.

[H. Peter Anvin]

On 05/17/2010 06:30 AM, Samuel Thibault wrote:
> Srinivas Nayak, le Mon 17 May 2010 15:43:17 +0530, a écrit :
>> After some more research, i foind that
>>
>> syscall(SYS_gettid)
>>
>> returns LWP id. Isn't this correct?
> 
> It is correct only on Linux, but yes.
> 

For libc's notion of the current thread, pthread_self(3).

	-hpa