From: Simon Strandgaard <0bz63fz3m1qt3001@...>
Date: 2003-05-11T09:29:43+09:00
Subject: Re: RCR for child execution

On Sun, 11 May 2003 05:39:31 +0900, Brian Candler wrote:

> On Sun, May 11, 2003 at 01:27:31AM +0900, Simon Strandgaard wrote:
>> Ruby-child-processes inherit stdout/stderr,  not rb_stdout, rb_stderr.
>> From C/C++ I cannot use stdout/stderr.  
> 
> What do you mean, "from C/C++ I cannot use stdout/stderr"??

Everything is OK when your application starts up, stdout/stderr works
fine. Then you initialize ruby and redirects its output elsewhere.
Now stdout/stderr doesn't work any longer.

I tried restoring stdout/stderr to the console again, but this 
affects the "system" call in ruby, see "process.c" that stdout/stderr
is being used. 

After redirecting rubys output, you cannot use stdout/stderr.

> cat main.cpp
#include <unistd.h>    // pipe, select
#include <sys/ioctl.h> // FIONREAD
#include <iostream>
#include <cstdio>
#include <fstream>
#include <ruby.h>      // rb_xxx

extern "C" {
        VALUE rb_defout;
        VALUE rb_stdout;
        VALUE rb_stderr;
}

int main(int argc, char *argv[]) {
        using namespace std;
        int pipes[2];
        if(pipe(pipes)) exit(-1);

        int bak_stdout = dup(fileno(stdout));
        int bak_stderr = dup(fileno(stderr));
        cout << "backups: stdout=" << bak_stdout <<
                " stderr=" << bak_stderr << endl;
        FILE *fd_out = fdopen(bak_stdout, "a");
        FILE *fd_err = fdopen(bak_stderr, "a");

        ruby_init();
        ruby_init_loadpath();
        VALUE params[2];
        params[0] = INT2FIX(pipes[1]);
        params[1] = rb_str_new2("w");
        VALUE w = rb_class_new_instance(2, params, rb_path2class("IO"));
        rb_gv_set("$defout", w);
        rb_gv_set("$stdout", w);
        rb_gv_set("$stderr", w);

        int new_stdout = dup2(bak_stdout, 1);
        int new_stderr = dup2(bak_stdout, 2);
        fprintf(fd_out, "new: stdout=%d stderr=%d\n", new_stdout, new_stderr);

        stdout = fdopen(new_stdout, "a"); // BOOM!
        stderr = fdopen(new_stderr, "a"); // BOOM!

        fprintf(fd_out, "bak_stdout\n");
        cout << "cout is working again" << endl;

        rb_eval_string("sleep 1; $stdout.puts 'aa';"
                " puts 'hello'; system('ls a.c xx'); sleep 1");

        close(pipes[0]);
        close(pipes[1]);
        return 0;
}
> cat Makefile
RUBY=$(HOME)/install/language/ruby-1.8.0
LIBS=$(RUBY)/libruby-static.a -lcrypt
all:
        g++ main.cpp -lc_r -I$(RUBY) $(LIBS) -Wall
>

Well, there is no thread to flush the pipe.. but this is not important
here!  What is important is that system('ls a.c xx')'s output goes to
stdout/stderr,  is mixed up with C's output.

If I remove those 2 lines containing "BOOM!" then system's output will go
to the pipe. 

After redirection I cannot use stdout/stderr!

Making this possible would require changes to ruby.. this is what my RCR
proposal is about.  



--
Simon Strandgaard