[Bug libstdc++/12855] Thread safety problems in ios_base::Init

[carlo at gcc dot gnu dot org]

------- Additional Comments From carlo at gcc dot gnu dot org  2003-12-14 03:45 -------
There is another problem with the patch.
As the old comments state:

        // NB: Allows debugger applications use of the standard streams
!       // from operator new. _S_ios_base_init must be incremented in
!       // _S_ios_create _after_ initialization is completed.
        static bool
!       _S_initialized() { return _S_ios_base_init; }

the flag that things are initialized must be set
AFTER things are initialized.  You'd break this function
with your patch:

*************** namespace std 
*** 80,86 ****
  
    ios_base::Init::Init()
    {
!     if (_S_ios_base_init == 0)
        {
  	// Standard streams default to synced with "C" operations.
  	_S_synced_with_stdio = true;
--- 80,86 ----
  
    ios_base::Init::Init()
    {
!     if (__exchange_and_add(&_S_references, 1) == 0)
        {
  	// Standard streams default to synced with "C" operations.
  	_S_synced_with_stdio = true;
*************** namespace std 
*** 110,124 ****
  	wcin.tie(&wcout);
  	wcerr.flags(ios_base::unitbuf);
  #endif
- 
- 	_S_ios_base_init = 1;
        }
-     ++_S_ios_base_init;
    }
  

As this increments _S_references at the beginning
and not at the end.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12855