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Buffer.add_channel hangs
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Date: -- (:)
From: Fabrice Le Fessant <fabrice.le_fessant@i...>
Subject: Re: [Caml-list] Buffer.add_channel hangs
Hi,

Maybe you should just use (in_channel_length ic) to get the size of the
file before hand, so that you can directly create a string with that
size instead of a Buffer.t ?

Regards,
--Fabrice

Stas Miasnikou wrote, On 03/18/2010 07:47 AM:
> On 3/18/10, Martin Jambon <martin.jambon@ens-lyon.org> wrote:
>> Stas Miasnikou wrote:
>>> OCaml 3.11.1, OpenBSD 4.6, i386.
>>>
>>> I am trying to read whole file by doing:
>>>
>>> let read_file_bin name =
>>>   let ic = open_in_bin name in
>>>   let b = Buffer.create 1024 in
>>>   (try Buffer.add_channel b ic max_int with _ -> ()); (* <-- HERE *)
>>>   close_in ic;
>>>   Array.init (Buffer.length b) (fun i -> int_of_char (Buffer.nth b i))
>>>
>>> but it hangs on the line marked. Am I doing something wrong?
>> The problem is max_int and the fact that Buffer.add_channel and
>> Buffer.resize
>>  do not check for this possibility:
>>
>> let add_channel b ic len =
>>   if b.position + len > b.length then resize b len;
>>   really_input ic b.buffer b.position len;
>>   b.position <- b.position + len
>>
>> Something like the following would be better:
>>
>> let add_channel b ic len =
>>   if len < 0 || len > Sys.max_string_length then
>>     invalid_arg "Buffer.add_channel";
>>   ...
> 
> Oh, never thought OCaml has bugs! ;-)
> 
>> Since you uncovered this problem, please kindly submit a proper bug report
>> at
>>   http://caml.inria.fr/mantis
> 
> I've submitted it.
> 
>> (and figure what to do if the file is larger than 16MB on 32-bit systems)
>>
>> Of course, you can see from the implementation of the Buffer module that a
>> string of your maximum length is created no matter what, which you surely
>> want
>> to avoid especially on 64-bit systems where Sys.max_string_length is very
>> large.
> 
> Erm... yes. I think I follow the other advice and will use Bigarray.
> 
> Stas
> 
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-- 
Fabrice LE FESSANT
Chercheur, Equipe ASAP
(As Scalable As Possible)
http://www.lefessant.net/

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