IO.pipe → array

Creates a pair of pipe endpoints (connected to each other) and returns them as a two-element array of IO objects: [ read_file, write_file ]. Not available on all platforms.

In the example below, the two processes close the ends of the pipe that they are not using. This is not just a cosmetic nicety. The read end of a pipe will not generate an end of file condition if there are any writers with the pipe still open. In the case of the parent process, the rd.read will never return if it does not first issue a wr.close.

rd, wr = IO.pipe

if fork
  wr.close
  puts "Parent got: <#{rd.read}>"
  rd.close
  Process.wait
else
  rd.close
  puts "Sending message to parent"
  wr.write "Hi Dad"
  wr.close
end

produces:

Sending message to parent
Parent got: <hi dad></hi>

Source Code

/*
*  call-seq:
*     IO.pipe -> array
*  
*  Creates a pair of pipe endpoints (connected to each other) and
*  returns them as a two-element array of <code>IO</code> objects:
*  <code>[</code> <i>read_file</i>, <i>write_file</i> <code>]</code>. Not
*  available on all platforms.
*     
*  In the example below, the two processes close the ends of the pipe
*  that they are not using. This is not just a cosmetic nicety. The
*  read end of a pipe will not generate an end of file condition if
*  there are any writers with the pipe still open. In the case of the
*  parent process, the <code>rd.read</code> will never return if it
*  does not first issue a <code>wr.close</code>.
*     
*     rd, wr = IO.pipe
*     
*     if fork
*       wr.close
*       puts "Parent got: <#{rd.read}>"
*       rd.close
*       Process.wait
*     else
*       rd.close
*       puts "Sending message to parent"
*       wr.write "Hi Dad"
*       wr.close
*     end
*     
*  <em>produces:</em>
*     
*     Sending message to parent
*     Parent got: <Hi Dad>
*/

static VALUE
rb_io_s_pipe(klass)
   VALUE klass;
{
#ifndef __human68k__
   int pipes[2], state;
   VALUE r, w, args[3];

#ifdef _WIN32
   if (_pipe(pipes, 1024, O_BINARY) == -1)
#else
   if (pipe(pipes) == -1)
#endif
       rb_sys_fail(0);

   args[0] = klass;
   args[1] = INT2NUM(pipes[0]);
   args[2] = INT2FIX(O_RDONLY);
   r = rb_protect(io_new_instance, (VALUE)args, &state);
   if (state) {
       close(pipes[0]);
       close(pipes[1]);
       rb_jump_tag(state);
   }
   args[1] = INT2NUM(pipes[1]);
   args[2] = INT2FIX(O_WRONLY);
   w = rb_protect(io_new_instance, (VALUE)args, &state);
   if (state) {
       close(pipes[1]);
       if (!NIL_P(r)) rb_io_close(r);
       rb_jump_tag(state);
   }
   rb_io_synchronized(RFILE(w)->fptr);

   return rb_assoc_new(r, w);
#else
   rb_notimplement();
   return Qnil;                /* not reached */
#endif
}