[Caml-list] Strange File IO bug

[Caml-list] Strange File IO bug

[Dmitriy Musatkin]

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Hi all,

I maintain a small OCaml program that generates some data, writes it to a
temporary file and creates another process, which then reads that temporary
file. Recently, I've received a few reports from users that the program
generates an empty file when it should not. All of the affected users run
either 64bit Win7 or Win10. I have access to one of those users' machines,
and I can reproduce the issue consistently, however I'm not able to
reproduce the issue on any other machine.

The file io part looks something like following:
let oc = open_out_bin file in
output_string oc s;
close_out oc

The string "s" has non-zero size. The out channel has non-zero length and
doing Unix.stat on the file after its closed shows non-zero size. However,
both the newly created process and Windows see the file as empty after the
program exits.

Any ideas on what might be happening?

Thanks,
Dmitriy

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Re: [Caml-list] Strange File IO bug

[Adrien Nader]

Hi,

On Tue, Jul 26, 2016, Dmitriy Musatkin wrote:
> Hi all,
> 
> I maintain a small OCaml program that generates some data, writes it to a
> temporary file and creates another process, which then reads that temporary
> file. Recently, I've received a few reports from users that the program
> generates an empty file when it should not. All of the affected users run
> either 64bit Win7 or Win10. I have access to one of those users' machines,
> and I can reproduce the issue consistently, however I'm not able to
> reproduce the issue on any other machine.
> 
> The file io part looks something like following:
> let oc = open_out_bin file in
> output_string oc s;
> close_out oc
> 

Most probably, "flush oc" before "close oc": out_channel is buffered. :) 

-- 
Adrien Nader

Re: [Caml-list] Strange File IO bug

[Gerd Stolpmann]

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Am Mittwoch, den 27.07.2016, 18:56 +0200 schrieb Adrien Nader:
> Hi,
> 
> On Tue, Jul 26, 2016, Dmitriy Musatkin wrote:
> > Hi all,
> > 
> > I maintain a small OCaml program that generates some data, writes it to a
> > temporary file and creates another process, which then reads that temporary
> > file. Recently, I've received a few reports from users that the program
> > generates an empty file when it should not. All of the affected users run
> > either 64bit Win7 or Win10. I have access to one of those users' machines,
> > and I can reproduce the issue consistently, however I'm not able to
> > reproduce the issue on any other machine.
> > 
> > The file io part looks something like following:
> > let oc = open_out_bin file in
> > output_string oc s;
> > close_out oc
> > 
> 
> Most probably, "flush oc" before "close oc": out_channel is buffered. :) 

No. close implies flush.

Another cause could be a network drive, and a synchronization issue.

Gerd



> -- 
> Adrien Nader
> 

-- 
------------------------------------------------------------
Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
My OCaml site:          http://www.camlcity.org
Contact details:        http://www.camlcity.org/contact.html
Company homepage:       http://www.gerd-stolpmann.de
------------------------------------------------------------


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