[m-rev.] for review: fix bug #161

[Paul Bone]

On Mon, May 20, 2013 at 03:43:21PM +1000, Julien Fischer wrote:
>
>
> On Mon, 20 May 2013, Paul Bone wrote:
>
>> On Mon, May 20, 2013 at 01:42:47PM +1000, Julien Fischer wrote:
>>>
>>> Fix bug #161.
>>>
>>> In C grades, closing a file stream multiple times can lead to a segmentation
>>> fault on some systems (e.g. Linux), whereas on others (e.g. Mac OS X) an
>>> io.error exception is thrown.  (The difference is due to differences in the
>>> semantics of fclose.)  Try to avoid the former case by checking that the
>>> stream handle is non-NULL before we attempt to close it.  (mercury_close
>>> zeros
>>> out the relevant bits of the MercuryFile structure when we close a stream
>>> so,
>>> the stream handle is set to NULL the first time we close the stream.)
>>>
>>> library/io.m:
>>>   As above.
>>>
>>
>> Try to wrap the text in the log message a little better.  Or is this Gmail
>> making life hard?
>
> Gmail; if you know how to stop it doing that then let me know.

I fix this by using mutt.  You can sync your g-mail mailboxes with
offlineimap and then use mutt locally.  You'll need an MTA on your
workstation.

>> Other than that the patch is fine.
>
> I have encountered another interesting problem in attempting to produce
> a test case for this.   The following program attempts to catch the
> exception thrown when we call io.close_output/3 twice in a row on the
> same file handle:
>
>     io.open_output("bug161b.txt", OpenResult, !IO),
>     (
>         OpenResult = ok(File),
>         ( try [io(!IO)] (
>             io.close_output(File, !IO),
>             io.close_output(File, !IO)
>           )
>         then
>             true
>         catch Error ->
>             Msg = io.error_message(Error),
>             io.write_string(Msg, !IO),
>             io.nl(!IO)
>         )
>     ;
>         OpenResult = error(_)
>     ).
>
> On Linux, it works in hlc.gc, but in asm_fast.gc it causes a
> segmentation fault after the code in the catch goal has been executed.
> I'm looking into this at the moment.

I'd love to know what's causing that.


-- 
Paul Bone
http://www.bone.id.au