* how does fork() copy threads of a process in multi-processor (SMP)
2011-03-10 16:55 ` Mulyadi Santosa
@ 2011-03-10 18:29 ` Josh Cartwright
2011-03-11 6:58 ` lalit mohan tripathi
1 sibling, 0 replies; 4+ messages in thread
From: Josh Cartwright @ 2011-03-10 18:29 UTC (permalink / raw)
To: kernelnewbies
On Thu, Mar 10, 2011 at 11:55:35PM +0700, Mulyadi Santosa wrote:
> Hi...
>
> On Thu, Mar 10, 2011 at 22:05, lalit mohan tripathi
> <lalit.tripathi@gmail.com> wrote:
> > I've a general question: In Multiprocessor (Multi-Core) (SMP)
> > environment how does fork system call (do_fork() related code)
> > maintain the synchronization in case the threads of a process are
> > running on different processors? E.g. it can happen that the fork()
> > is called by cpu-0 thread and other thread of same process is
> > executing on cpu-1.
>
> well, AFAIK, the newly born child, at least when they are just about
> to kick in into the run queue (in any CPU), is actually still inside
> the parent's code path. Or in simpler word, they are still bound in
> the same core/processor they are created. Therefore, there's no
> problem regarding task struct duplication etc
Also, please keep in mind that fork() does NOT cause all the threads of the
parent process to propogate to the child process. Only the thread that called
fork() is duplicated. From `man 2 fork':
* The child process is created with a single thread -- the one that called
fork(). The entire virtual address space of the parent is replicated in the
child, including the states of mutexes, condition variables, and other pthreads
objects; the use of pthread_atfork(3) may be helpful for dealing with problems
that this can cause.
--
joshc
^ permalink raw reply [flat|nested] 4+ messages in thread* how does fork() copy threads of a process in multi-processor (SMP)
2011-03-10 16:55 ` Mulyadi Santosa
2011-03-10 18:29 ` Josh Cartwright
@ 2011-03-11 6:58 ` lalit mohan tripathi
1 sibling, 0 replies; 4+ messages in thread
From: lalit mohan tripathi @ 2011-03-11 6:58 UTC (permalink / raw)
To: kernelnewbies
On Thu, Mar 10, 2011 at 10:25 PM, Mulyadi Santosa
<mulyadi.santosa@gmail.com> wrote:
> Hi...
>
> On Thu, Mar 10, 2011 at 22:05, lalit mohan tripathi
> <lalit.tripathi@gmail.com> wrote:
>> I've a general question: ?In Multiprocessor (Multi-Core) (SMP)
>> environment how does ?fork system call ?(do_fork() related code)
>> maintain the synchronization in case the threads of a process are
>> running on different processors? ?E.g. it can happen that the fork()
>> is called by cpu-0 thread and other thread of same process is
>> executing on cpu-1.
>
> well, AFAIK, the newly born child, at least when they are just about
> to kick in into the run queue (in any CPU), is actually still inside
> the parent's code path. Or in simpler word, they are still bound in
> the same core/processor they are created. Therefore, there's no
> problem regarding task struct duplication etc
>
> is that what you mean?
>
> --
> regards,
>
> Mulyadi Santosa
> Freelance Linux trainer and consultant
>
> blog: the-hydra.blogspot.com
> training: mulyaditraining.blogspot.com
>
Ok, I got the answer: Only the thread calling fork() gets copied. Thanks.
^ permalink raw reply [flat|nested] 4+ messages in thread