Обсуждение: A portable code question

In the little fix I came up with for psql last night, I need to be able
to ensure that something sent to a pipe (and then to stdout) completes 
before issuing the prompt directly to stdout.  

I did this with: "system ('sleep 1');", but I'm fairly sure that is 
not portable nor does it ENSURE completion. 

What's the proper way to do this?  And what's a good book on writing
portable code?
--
Mike Nolan

Assuming you're using file streams to write to the pipe, fflush() will do
the trick.

> -----Original Message-----
> From: pgsql-hackers-owner@postgresql.org
> [mailto:pgsql-hackers-owner@postgresql.org]On Behalf Of
> nolan@celery.tssi.com
> Sent: Thursday, June 26, 2003 2:20 PM
> To: pgsql hackers list
> Subject: [HACKERS] A portable code question
>
>
> In the little fix I came up with for psql last night, I need to be able
> to ensure that something sent to a pipe (and then to stdout) completes
> before issuing the prompt directly to stdout.
>
> I did this with: "system ('sleep 1');", but I'm fairly sure that is
> not portable nor does it ENSURE completion.
>
> What's the proper way to do this?  And what's a good book on writing
> portable code?
> --
> Mike Nolan
>
> ---------------------------(end of broadcast)---------------------------
> TIP 8: explain analyze is your friend
>

> Assuming you're using file streams to write to the pipe, fflush() will do
> the trick.

The problem is that the pipe (from \o |tee xxxx) is intermingling writes
to stdout by tee with direct writes to stdout from within psql.

I do issue a fflush, because that's necessary to make the pipe do its 
thing, but the next line of code also does a write to stdout and the pipe 
generally doesn't have time to complete that write to stdout, resulting
in intermingled output.  (fflush makes sure the pipe GETS the stream,
it doesn't wait around to make sure it's DONE with it, probably because
there's no way for whatever the pipe calls to report back when it is done.)

This is a bit of a hack, but adding an option to the \o code so that it 
writes simultaneously to the pipe and to stdout instead of using tee 
looks like a lot more work, especially since the code appears to have a 
couple of other places where intermingling to stdout is possible,
especially if readline is used.

Throwing in "system('sleep 1');" was the way I resolved the timing 
question here, but that may not be portable enough for inclusion into 
the code base.
--
Mike Nolan

Or if you want this behaviour all the time, one call of setvbuf(mypipe,(char *)0,_IONBF,0);
should do the trick (much easier than remebering to have to call fflush()
all the time).

If not using streams, and just calling write(), then you probably don't have
to worry.

andrew

BTW, "system('sleep 1');" probably won't compile, and 'system("sleep 1");'
is bad news. Try "man 3 sleep" for more info.

> Assuming you're using file streams to write to the pipe, fflush() will
> do the trick.
>
>> -----Original Message-----
>> From: pgsql-hackers-owner@postgresql.org
>> [mailto:pgsql-hackers-owner@postgresql.org]On Behalf Of
>> nolan@celery.tssi.com
>> Sent: Thursday, June 26, 2003 2:20 PM
>> To: pgsql hackers list
>> Subject: [HACKERS] A portable code question
>>
>>
>> In the little fix I came up with for psql last night, I need to be
>> able to ensure that something sent to a pipe (and then to stdout)
>> completes before issuing the prompt directly to stdout.
>>
>> I did this with: "system ('sleep 1');", but I'm fairly sure that is
>> not portable nor does it ENSURE completion.
>>
>> What's the proper way to do this?  And what's a good book on writing
>> portable code?
>> --
>> Mike Nolan
>>
>> ---------------------------(end of
>> broadcast)--------------------------- TIP 8: explain analyze is your
>> friend
>>
>
>
> ---------------------------(end of
> broadcast)--------------------------- TIP 7: don't forget to increase
> your free space map settings