Re: replacing new, getting sane allocator/iostreams behavior

[Carlo Wood <carlo at alinoe dot com>]

On Tue, Jul 03, 2001 at 06:03:51PM -0700, Benjamin Kosnik wrote:
> Your patch won't work: it disables the sync_with_stdio functionality, for 
> starters.

It does?  How?  I started off with the source of 3.0 which was:

  ios_base::Init::Init()
  {
    if (++_S_ios_base_init == 1)
      {
        // Standard streams default to synced with "C" operations.
        ios_base::Init::_S_synced_with_stdio = true;
        _S_ios_create(ios_base::Init::_S_synced_with_stdio);
      }
  }

and I changed that into:

  ios_base::Init::Init()
  {
    if (_S_ios_base_init == 0)
    {
        // Standard streams default to synced with "C" operations.
        ios_base::Init::_S_synced_with_stdio = true;
        _S_ios_create(ios_base::Init::_S_synced_with_stdio);
    }
    ++_S_ios_base_init;
  }

How does that disables the sync_with_stdio functionality?

> Also, with changes to the allocator class and other bits, I'm 
> not quite sure this is possible. 

It should be as I looked at this independant of other code (I don't even
know how that looks like or what it does).  The changes I proposed do
not change the functionality in ANY way - except that it STILL works
in cases where it now fails (namely when ios_base::Init is created
from within operator new).  When there is NOT an ios_base::Init created
from within operator new, my changes (should) have no effect at all.
Therefore it is impossible that it would break something.

If I am wrong then please clarify what I am missing :)

> -benjamin

A sumary of the proposed change is as follows.
At the moment, the only possiblity is to NOT create a ios_base::Init
anywhere during a call to operator new (well, at least - that wouldn't
have any effect).  This results in a program flow that can only look like:

ios_base::Init::Init()
       |
       V
    _S_ios_create()
           |
           V
        operator new()		[ we can not use std::cout in operator new ]
           |
         return
           |
           V
    _S_ios_create()
       |
     return
       |
       V
ios_base::Init::Init()


After the change, it is also allowed to have:


ios_base::Init::Init()
       |
       V
    _S_ios_create()
           |
           V
        operator new()
               |
               V
	    ios_base::Init::Init()
		   |
		   V
		_S_ios_create()           ^
		       |                  |
		       V                  |
		    operator new()        |_ actual initialization
		       |                  |
		     return               |
		       |                  |
		       V                  |
		_S_ios_create()           v
		   |
		 return
		   |
		   V
	    ios_base::Init::Init()	(first Init object that is successfully created)
               |
             return
               |
               V
        operator new()		[ here we can use std::cout in operator new ]
           |
         return
           |
           V
    _S_ios_create()	(returns without (additional) effect)
       |
     return
       |
       V
ios_base::Init::Init()      (second Init object that is successfully created)


-- 
Carlo Wood <carlo@alinoe.com>