[Caml-list] input_line is blocking

[Caml-list] input_line is blocking

[Warp]

Hi
I'm running "ocamlc" by using Unix.open_process_full in order to write an
automatic compiler.
Right now, it's working fine, but I got now a problem with input_line :

after running open_process_full , i'm first reading all its stdout lines of
the process until End_of_file is raised, then all its stderr lines using the
same function.

It has work fine for few weeks now, but now I found that in some cases
input_line will block, not raising End_of_file.
Actually I got the following errors (on purpose ! ) in one of my test files
:

File "player.ml", line 16, characters 6-66:
Warning: this expression should have type unit.
The implementation player.ml does not match the interface player.cmi :
Modules do not match:
  sig
     type 'a t = 'a array
     ...
     ....
  end
is not included in
   sig
     ...........
   end
The field 'c_value' is required but not provided

I tried to correct few errors, and if I correct enough of them, it works
 the call to input_line on the stdout where NO DATA is written is raising
End_of_file ) , but if correct some other errors, I won't work again...

Perhaps something to do with bufferization ?
If ocamlc generates too much data on stderr, then he waits for the calling
process to read that data, but the process is currently reading on its
stdout.... And vice-versa for ocamldep ( which generates a lot of data on
its stdout )

Any help would be apprecied

Nicolas Cannasse

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Re: [Caml-list] input_line is blocking

[Oliver Bandel]

On Fri, 3 May 2002, Warp wrote:

> Hi
> I'm running "ocamlc" by using Unix.open_process_full in order to write an
> automatic compiler.
> Right now, it's working fine, but I got now a problem with input_line :
> 
> after running open_process_full , i'm first reading all its stdout lines of
> the process until End_of_file is raised, then all its stderr lines using the
> same function.
> 
> It has work fine for few weeks now, but now I found that in some cases
> input_line will block, not raising End_of_file.

In networking-applications, or when using pipes you
can't use C's standard-lib and have to use the
Unix-API directly (open/read/write/close).

Ocaml's libraries seem to be wrapping C's standard-lib
for it's normal I/O and the Unix-API for it's Unix-module.

So, if you want to use pipes/sockets, you have to use the
Unix-module's I/O-functions!

But I think in Ocaml it is not a problem to write wrapper-code.
In C this would be much effort, but I think in Ocaml it's
easy to write a network-lib....

Ciao,
   Oliver

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Re: [Caml-list] input_line is blocking

[Remi VANICAT]

"Warp" <warplayer@free.fr> writes:

> Hi

> Perhaps something to do with bufferization ?
> If ocamlc generates too much data on stderr, then he waits for the calling
> process to read that data, but the process is currently reading on its
> stdout.... And vice-versa for ocamldep ( which generates a lot of data on
> its stdout )

yes, I believe this is the problem.

the only solution maybe to use select

-- 
Rémi Vanicat
vanicat@labri.u-bordeaux.fr
http://dept-info.labri.u-bordeaux.fr/~vanicat
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Re: [Caml-list] input_line is blocking

[Gerd Stolpmann]

On 2002.05.03 14:18 Warp wrote:
> Hi
> I'm running "ocamlc" by using Unix.open_process_full in order to write an
> automatic compiler.
> Right now, it's working fine, but I got now a problem with input_line :
> 
> after running open_process_full , i'm first reading all its stdout lines of
> the process until End_of_file is raised, then all its stderr lines using the
> same function.
> 
> It has work fine for few weeks now, but now I found that in some cases
> input_line will block, not raising End_of_file.

I wrote a library exactly for such advanced usage of sub processes:
http://www.ocaml-programming.de/packages/documentation/shell/

For example, to call ocamlc one would do:

open Shell
let stdout = Buffer.create 16 in
let stderr = Buffer.create 16 in
call ~stdout:(to_buffer stdout) ~stderr:(to_buffer stderr) [ cmd "ocamlc" args ]

The Shell library includes the necessary logic to read from multiple
file descriptors (using Unix.select). 

One drawback: Shell works only for Unix (because of Unix.fork). I think that you have
to use multi-threading for a platform-independent solution.

Gerd
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