Groups | Search | Server Info | Login | Register

Groups > comp.lang.awk > #171

Re: getline timeout (revisited)

Show all headers | View raw

In article <ioka93$13e$1@news.m-online.net>, Janis Papanagnou wrote:
> On 19.04.2011 16:09, j.eh@mchsi.com wrote:
>> In article <inmun6$lq1$1@speranza.aioe.org>, Janis Papanagnou wrote:
>>> I've been currently looking for a timeout option for getline in
>>> the context of an /inet/tcp/... socket communication with gawk.
>>>
>>> This topic had already been addressed here in c.l.a many many
>>> years ago, as my google search showed, but I haven't found any
>>> positive answers. Has there been something incorporated in gawk
>>> or xgawk, meanwhile, or is the status unchanged. I suppose the
>>> latter, but asking for a confirmation anyway.
>> 
>> [ Janis, I hit the wrong button. My intention was to post to
>> the group, not to send a personal email. Sorry about that. ]
> 
> Don't worry; in my mailbox only spam isn't welcome. :-)
> 
>> 
>> 
>> I find the discussions in the old threads interesting, but I have
>> a question. Let's assume we use PROCINFO to specify timeout like
>> this:
>> 
>>      PROCINFO["/inet/tcp/..", "TIMEOUT"] = 1000 (ms)
>> 
>> and a value of 0 means the default behavior i.e. no timeout.
> 
> Yes.
> 
>> 
>> Also, assume the existence of a builtin either in the gawk source
>> or in a extension:
>> 
>>      readline("/inet/tcp/..")
> 
> Hmm.. - why a new function or builtin 'readline()' and not extending
> the functionality of 'getline'? (Shouldn't conflict given the PROCINFO
> approach.)

I don't know what extensions of 'getline' (or 'RS', or any other
builtin feature of the language) functionality will be required,
but all I know is that if those are in conflict with the required
semantics and rules of the language, Arnold isn't simply going to
accept it. So, one has to prove that the required functionality can't be
provided by a seperate builtin, and/or any proposed changes to 'getline'
functionality aren't going to violet the rules of the language etc. etc.
Besides, a seperate function provides lot more flexibility; Just
consider:

  readline("/inet/tcp/...", var, timeout)

'var' is pass by reference. You won't need PROCINFO or environment
variable for timeout specification, and won't even be limited to
returning only -1, 0 or 1.

> 
>> 
>> which other than being a function call behaves exactly like getline
>> w.r.t. RS, RT and setting fields. We modify 'readline' to handle
>> timeout anyway you think is suitable to serve our purpose. The question
>> is then, if a script using 'readline' going to look any different
>> than from the one that uses getline with exactly the same
>> modifications.
> 
> I don't understand what you're saying above, and what you're aiming at.
> 

If the use of 'getline' does not simplify things in the script compared
to a new function, then why bother trying to extend 'getline'?

Ok, let's just stick with getline and see if it can provide a
general solution; A solution specific to a particular problem
at hand isn't going to be good enough. The following example from
gawk-inet documentation, I believe, illustrates the most general
usage of getline. There isn't any need to throw input file and
related pattern/action, or even fields into the mix.

     BEGIN {
       RS = ORS = "\r\n"
       HttpService = "/inet/tcp/0/proxy/80"
       print "GET http://www.yahoo.com" |& HttpService
       PROCINFO[HttpService, "TIMEOUT"] = 1000
       while ((HttpService |& getline var) > 0)
          print var
       close(HttpService)
     }

I added the line with the PROCINFO entry, and used 'getline var'
instead of 'getline'. What other changes are needed so that we still
get the desired output with timeouts? If the answer is none whatsoever,
then probably won't need to consider the following:

1. Dealing with partial output in case of a timeout.
2. Handling of non-recoverable errors. What is getline
supposed to return if a timeout occurs?
3. Making sure there are finite number of retries in the
event of timeouts.
4. ?

Thanks,

John

>> If possible, please consider providing the outline
>> of such a script illustrating the usage of 'readline' or getline
>> with timeout.
> 
> In my specific primitive application - which is by no means meant to be
> a general example, covering all needs, or considering any corner cases -
> it was just something like (simplified code)...
> 
>   BEGIN { P = "/inet/tcp/0/a.b.c.d/e" }
>         { print some_funct($0) |&  P }
>   /pat/ { P |& getline ; do_sth_w($0) }
>   END   { close(P) }
> 
> which might, with timeouts, morph to something like...
> 
>   BEGIN { P = "/inet/tcp/0/a.b.c.d/e"
>           PROCINFO[ P, "TIMEOUT"] = 1000
>         }
> 
>         { print some_funct($0) |&  P }
> 
>   /pat/ { if( (P |& getline) > 0) do_sth_w($0)
>           else print "Error:", PROCINFO[ P, "ERROR"]
>         }
> 
>   END   { close(P) }
> 
> 
> Using PROCINFO as a means to return the error is just an ad hoc thought
> based on your timeout setting example. (So feel free to ignore it and
> introduce something else.)
> 
>> To keep things uniform, assume we parse ERRNO to
>> find out the cause of error. Not very gifted when it comes to writing
>> awk scripts that doesn't look like C, so I hope you understand my
>> request in this context. 
> 
> If I've misunderstood your request, please clarify.
> 
> Thanks.
> 
> Janis
> 
>> 
>> Thanks,
>> 
>> John
>> 
>>>
>>> Thanks.
>>>
>>> Janis
> 

Back to comp.lang.awk | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

getline timeout (revisited) Janis Papanagnou <janis_papanagnou@hotmail.com> - 2011-04-08 14:23 +0200
  Re: getline timeout (revisited) arnold@skeeve.com (Aharon Robbins) - 2011-04-10 18:49 +0000
  Re: getline timeout (revisited) j.eh@mchsi.com - 2011-04-19 09:09 -0500
    Re: getline timeout (revisited) Janis Papanagnou <janis_papanagnou@hotmail.com> - 2011-04-19 17:38 +0200
      Re: getline timeout (revisited) j.eh@mchsi.com - 2011-04-20 06:51 -0500
        Re: getline timeout (revisited) Janis Papanagnou <janis_papanagnou@hotmail.com> - 2011-04-20 14:20 +0200
          Re: getline timeout (revisited) j.eh@mchsi.com - 2011-04-20 08:21 -0500
            Re: getline timeout (revisited) j.eh@mchsi.com - 2011-04-21 05:46 -0500
            Re: getline timeout (revisited) arnold@skeeve.com (Aharon Robbins) - 2011-04-22 13:55 +0000
              Re: getline timeout (revisited) Grant <omg@grrr.id.au> - 2011-04-23 06:50 +1000

csiph-web