From: Simon Strandgaard <0bz63fz3m1qt3001@...>
Date: 2003-05-13T23:33:10+09:00
Subject: Re: RCR for child execution

On Tue, 13 May 2003 23:44:53 +0900, Brian Candler wrote:

> On Tue, May 13, 2003 at 06:50:54PM +0900, Simon Strandgaard wrote:
>> > In the general case, your Ruby program could do lots of things which force
>> > a direct output to stdout/stderr. Here is one small valid Ruby program:
>> > 
>> >         pid = fork do
>> >           exec("ls /nonexistent")
>> >         end
>> >         Process.waitpid(pid)
>> > 
>> > How are you going to modify Ruby so that the output of those four lines are
>> > captured in the sandbox?
>> 
>> All "child-process" routines should parse rb_stdout to the children, in
>> this case fork.  I know I have only mentioned system&backquote before. 
>> Well all routines in Rubys Core which spawns children should do this. 
> 
> Not acceptable... this time I must insist that you answer the question :-)

OK.

 
> How exactly are you proposing to modify the Ruby interpreter so that the
> above four lines of Ruby code have their output captured?
> 
> "fork" has specific, well-defined semantics: it just calls the underlying
> Unix fork. "exec" has specific, well-defined semantics in the same way.
> Neither of them involves pipes.
> 
> What *exactly* do you want the two methods Kernel#fork and Kernel#exec to do
> instead of their currently defined behaviour?


Kernel#exec  does not spawn children.. no changes is necessary here.


Kernel#fork  does spawn a child.. changes to Rubys Core is necessary.
unix-fork inherit stdin/stdout/stderr from parent to the child process.
I want Rubys Kernel#fork to inherit rb_stdin/rb_stdout/rb_stderr from the
parent to the child process. 
But hey.. unix-fork() does not take any arguments.  Is this possible?
My guess - Yes this should be possible. Here is some pseudo code.

void Kernel#fork() {
    backup_stdout = stdout;      /* what i want */
    stdout = rb_stdout;          /* what i want */
    pid = fork();
    if(pid == 0)
        stdout = backup_stdout;  /* what i want */
}

Again assignment to stdout is illegal.. freopen should be used. I just use
assignment in this pseudo-code in order to keep it simple. Further more
stderr/stdin is left out.. they should of cause also be redirected.

This way stdout/stderr/stdin should be untouched and remain usable in the C/C++
application.


Does it answer the question ?

--
Simon Strandgaard