Re: netcamlbox: checking the mail box without waiting

Hello,

Gerd Stolpmann wrote:
> On Di, 2010-03-23 at 15:50 +0000, Hugo Ferreira wrote:
snip..
>> Fatal error: exception Unix.Unix_error(20, "shm_open", "/camlbox_9838_0")
>> Raised by primitive operation at unknown location
>> Called from file "netcamlbox.ml", line 322, characters 4-21
> 
> 20 is ENOENT, so I guess you unlinked the shm object before.
>

Correct. I unlink the mbox as per your example.
No need to keep it around.

>> For testing purposes I used:
snip...
>> My question is: how do I go about avoiding the block
>> on a mailing box?
> 
> Well, generally you need some trigger from the worker, and a counter.
> The trigger should be a message the worker sends out when it freed a
> slot. The counter could be implemented inside the coordinator, or as a
> shared counter (i.e. as semaphore). That depends on a lot of details, so
> without knowing the code I cannot give an advice.
> 

Interesting. I was looking at it the other way around.
In other words workers wait on their mboxes for work.
In fact I had envisioned a common mbox for all task dispatch.

In the meantime I have looked at the mbox source code.
I realized that with a small change to camlbox_messages
my problem is solved. I have altered it to:

let camlbox_messages box =
   Netsys_posix.sem_getvalue box.sem.s_free_slots

Upon reflection I have come to realize that:

a) I am in fact using a global counter to push work
    onto idle workers (basically does as you suggested -
    use a counting semaphore).

b) I think that "camlbox_messages" should use a box because
    it is a:
    i) a value of a specific mbox and
    ii) allows faster access to the same information.

Might I suggest the above alteration to the API?

Thanks for the suggestions.

Regards,
Hugo F.


> Gerd
> 
>> TIA,
>> Hugo F.
>>
>>
>>
>>
>>
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> 
> 


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