GNU bug report logs - #10616
flush procedure for soft ports isn't called

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From: ludo <at> gnu.org (Ludovic Courtès)
To: Mark H Weaver <mhw <at> netris.org>
Cc: Ian Price <ianprice90 <at> googlemail.com>, 10616 <at> debbugs.gnu.org
Subject: bug#10616: flush procedure for soft ports isn't called
Date: Sat, 10 Mar 2012 23:14:39 +0100

Hi Mark,

Mark H Weaver <mhw <at> netris.org> skribis:

> ludo <at> gnu.org (Ludovic Courtès) writes:
>
>> Ian Price <ianprice90 <at> googlemail.com> skribis:
>>
>>>  
>>> -  if (pt->write_pos > pt->write_buf)
>>> -    {
>>> -      /* write the byte. */
>>> -      scm_call_1 (SCM_SIMPLE_VECTOR_REF (stream, 0),
>>> -		  SCM_MAKE_CHAR (*pt->write_buf));
>>> -      pt->write_pos = pt->write_buf;
>>> -  
>>> -      /* flush the output.  */
>>> -      {
>>> -	SCM f = SCM_SIMPLE_VECTOR_REF (stream, 2);
>>> +  SCM f = SCM_SIMPLE_VECTOR_REF (stream, 2);
>>> +
>>> +  if (scm_is_true (f))
>>> +    scm_call_0 (f);
>>>  
>>> -	if (scm_is_true (f))
>>> -	  scm_call_0 (f);
>>> -      }
>>> -    }
>>>  }
>>
>> It’s a bit late to reply (sorry, Ian!), but the reason it took me so
>> long, is that I wanted to understand the rationale for the ‘if’, and the
>> implications of dropping it (which I never got around to, as you can
>> see.  ;-))
>>
>> Mark: what’s your take on this?  I’m especially concerned with
>> undesirable side effects in user code.
>
> I searched libguile for occurrences of 'write_pos' and 'write_buf', and
> convinced myself that Ian's analysis was indeed correct.  The write
> buffer is not used by the core ports code.  Writes are forwarded
> directly to the write function of the specific port type, which may use
> the write buffer if it wishes to, but need not.  The write buffer is
> used only by certain types of ports: currently string ports and file
> ports.  It is not used by soft ports.

OK.  Thanks for the detailed analysis!

Ludo’.

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