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Subject: Re: [OMPI devel] RFC: System V Shared Memory for Open MPI
From: Samuel K. Gutierrez (samuel_at_[hidden])
Date: 2010-06-02 13:58:41


Good point - I forgot about that.

--
Samuel K. Gutierrez
Los Alamos National Laboratory
On Jun 2, 2010, at 11:40 AM, Jeff Squyres wrote:
> Don't forget that the RML is also used to broadcast the success/ 
> failure of the creation of the shared memory segment.
>
> If the RML goes away, be sure that you can still determine that  
> without hanging.
>
> Personally, I still don't see the problem with using the RML stuff...
>
>
> On Jun 2, 2010, at 1:07 PM, Samuel K. Gutierrez wrote:
>
>> Hi George,
>>
>> That may work - I'll try it.
>>
>> Thanks!
>>
>> --
>> Samuel K. Gutierrez
>> Los Alamos National Laboratory
>>
>> On Jun 2, 2010, at 10:59 AM, George Bosilca wrote:
>>
>>> How about ftok ? The init function takes a file_name as argument,
>>> and this file name is unique per instance of the shared memory
>>> region we want to create. We can use this file name with ftok to
>>> create a unique key_t that can be used by shmget to retrieve the
>>> shared memory identifier.
>>>
>>> george.
>>>
>>> On Jun 2, 2010, at 11:53 , Samuel K. Gutierrez wrote:
>>>
>>>> On Jun 2, 2010, at 8:49 AM, Jeff Squyres wrote:
>>>>
>>>>> On Jun 2, 2010, at 10:44 AM, George Bosilca wrote:
>>>>>
>>>>>>> Not sure what you mean here.  common/sm may create new shmem
>>>>>>> segments at any time (e.g., during coll sm).  The RML message
>>>>>>> exchange is to ensure that only 1 process creates and
>>>>>>> initializes the segment and then all the others just attach to  
>>>>>>> it.
>>>>>>
>>>>>> Absolutely not! The RML messaging is not about initializing the
>>>>>> shared memory segment. As stated on my original text it has only
>>>>>> one purpose: to ensure the file used by mmap is created
>>>>>> atomically. The code for Windows do not exchange any RML messages
>>>>>> as the function to allocate the shared memory region provided by
>>>>>> the OS is atomic (exactly as the sysv one).
>>>>>
>>>>> I thought that Sam said that it was important that only 1 process
>>>>> shmctl/IPC_RMID...?
>>>>
>>>> Hi George,
>>>>
>>>> We are using RML messaging in the sysv code to exchange the shared
>>>> memory ID (generated by exactly one process).  I'm not sure how we
>>>> would go about passing along the shared memory ID without RML, but
>>>> any ideas are greatly appreciated.
>>>>
>>>> Thanks,
>>>> --
>>>> Samuel K. Gutierrez
>>>> Los Alamos National Laboratory
>>>>
>>>>>
>>>>> --
>>>>> Jeff Squyres
>>>>> jsquyres_at_[hidden]
>>>>> For corporate legal information go to:
>>>>> http://www.cisco.com/web/about/doing_business/legal/cri/
>>>>>
>>>>>
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>
>
> -- 
> Jeff Squyres
> jsquyres_at_[hidden]
> For corporate legal information go to:
> http://www.cisco.com/web/about/doing_business/legal/cri/
>
>
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