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

["bkoz at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

------- Additional Comments From bkoz at gcc dot gnu dot org  2003-12-10 00:17 -------

This would at least remove the corruption of _S_ios_base_init. I figure this is
less useful than the _S_once approach, but necessary no matter what.

Thoughts? I would like to fix this up for 3.4, regardless of how hypothetical
this issue is, or appears to be. I think this issue could, in fact, appear in
practice, either with dlopen or inadvertent (but legal) use of ios_base::Init.

-benjamin

-----

2003-12-09  Benjamin Kosnik  <bkoz@redhat.com>

	PR libstdc++/12855
	* include/bits/ios_base.h (_Callback_list): _M_refcount to
	_M_references.
	(Init::_S_ios_base_init): Change to _S_references, make atomic.
	* src/ios.cc: Adjust definition.
	* src/ios_init.cc (ios_base::Init::Init): Use __exchange_and_add.
	(ios_base::Init::~Init): Same.
	* testsuite/27_io/ios_base/cons/assign_neg.cc: Adjust line numbers.
	* testsuite/27_io/ios_base/cons/copy_neg.cc: Same.
	
Index: include/bits/ios_base.h
===================================================================
RCS file: /cvs/gcc/gcc/libstdc++-v3/include/bits/ios_base.h,v
retrieving revision 1.34
diff -c -p -r1.34 ios_base.h
*** include/bits/ios_base.h	12 Oct 2003 10:12:08 -0000	1.34
--- include/bits/ios_base.h	10 Dec 2003 00:14:44 -0000
*************** namespace std
*** 428,445 ****
        _Callback_list* 		_M_next;
        ios_base::event_callback 	_M_fn;
        int 			_M_index;
!       _Atomic_word		_M_refcount;  // 0 means one reference.
      
        _Callback_list(ios_base::event_callback __fn, int __index, 
  		     _Callback_list* __cb)
!       : _M_next(__cb), _M_fn(__fn), _M_index(__index), _M_refcount(0) { }
        
        void 
!       _M_add_reference() { __atomic_add(&_M_refcount, 1); }
  
        // 0 => OK to delete.
        int 
!       _M_remove_reference() { return __exchange_and_add(&_M_refcount, -1); }
      };
  
       _Callback_list*  	_M_callbacks;
--- 428,445 ----
        _Callback_list* 		_M_next;
        ios_base::event_callback 	_M_fn;
        int 			_M_index;
!       _Atomic_word		_M_references;  // 0 means one reference.
      
        _Callback_list(ios_base::event_callback __fn, int __index, 
  		     _Callback_list* __cb)
!       : _M_next(__cb), _M_fn(__fn), _M_index(__index), _M_references(0) { }
        
        void 
!       _M_add_reference() { __atomic_add(&_M_references, 1); }
  
        // 0 => OK to delete.
        int 
!       _M_remove_reference() { return __exchange_and_add(&_M_references, -1); }
      };
  
       _Callback_list*  	_M_callbacks;
*************** namespace std
*** 493,506 ****
        ~Init();
        
        // 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; }
  
      private:
!       static int 	_S_ios_base_init;
!       static bool	_S_synced_with_stdio;
      };
  
      // [27.4.2.2] fmtflags state functions
--- 493,505 ----
        ~Init();
        
        // NB: Allows debugger applications use of the standard streams
!       // from operator new. 
        static bool
!       _S_initialized() { return _S_references > 0; }
  
      private:
!       static _Atomic_word	_S_references;
!       static bool		_S_synced_with_stdio;
      };
  
      // [27.4.2.2] fmtflags state functions
Index: src/ios.cc
===================================================================
RCS file: /cvs/gcc/gcc/libstdc++-v3/src/ios.cc,v
retrieving revision 1.51
diff -c -p -r1.51 ios.cc
*** src/ios.cc	17 Oct 2003 14:47:30 -0000	1.51
--- src/ios.cc	10 Dec 2003 00:14:44 -0000
*************** namespace std 
*** 107,113 ****
  
    const int ios_base::_S_local_word_size;
  
!   int ios_base::Init::_S_ios_base_init = 0;
  
    bool ios_base::Init::_S_synced_with_stdio = true;
  
--- 107,113 ----
  
    const int ios_base::_S_local_word_size;
  
!   _Atomic_word ios_base::Init::_S_references;
  
    bool ios_base::Init::_S_synced_with_stdio = true;
  
Index: src/ios_init.cc
===================================================================
RCS file: /cvs/gcc/gcc/libstdc++-v3/src/ios_init.cc,v
retrieving revision 1.1
diff -c -p -r1.1 ios_init.cc
*** src/ios_init.cc	17 Oct 2003 14:47:30 -0000	1.1
--- src/ios_init.cc	10 Dec 2003 00:14:44 -0000
*************** 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;
    }
  
    ios_base::Init::~Init()
    {
!     if (--_S_ios_base_init == 1)
        {
  	// Catch any exceptions thrown by basic_ostream::flush()
  	try
--- 110,121 ----
  	wcin.tie(&wcout);
  	wcerr.flags(ios_base::unitbuf);
  #endif
        }
    }
  
    ios_base::Init::~Init()
    {
!     if (__exchange_and_add(&_S_references, -1) == 1)
        {
  	// Catch any exceptions thrown by basic_ostream::flush()
  	try
Index: testsuite/27_io/ios_base/cons/assign_neg.cc
===================================================================
RCS file: /cvs/gcc/gcc/libstdc++-v3/testsuite/27_io/ios_base/cons/assign_neg.cc,v
retrieving revision 1.6
diff -c -p -r1.6 assign_neg.cc
*** testsuite/27_io/ios_base/cons/assign_neg.cc	12 Oct 2003 10:12:09 -0000	1.6
--- testsuite/27_io/ios_base/cons/assign_neg.cc	10 Dec 2003 00:14:45 -0000
*************** void test01()
*** 41,45 ****
    io1 = io2;
  }
  // { dg-error "within this context" "" { target *-*-* } 41 } 
! // { dg-error "is private" "" { target *-*-* } 746 } 
  // { dg-error "operator=" "" { target *-*-* } 0 } 
--- 41,45 ----
    io1 = io2;
  }
  // { dg-error "within this context" "" { target *-*-* } 41 } 
! // { dg-error "is private" "" { target *-*-* } 745 } 
  // { dg-error "operator=" "" { target *-*-* } 0 } 
Index: testsuite/27_io/ios_base/cons/copy_neg.cc
===================================================================
RCS file: /cvs/gcc/gcc/libstdc++-v3/testsuite/27_io/ios_base/cons/copy_neg.cc,v
retrieving revision 1.6
diff -c -p -r1.6 copy_neg.cc
*** testsuite/27_io/ios_base/cons/copy_neg.cc	12 Oct 2003 10:12:09 -0000	1.6
--- testsuite/27_io/ios_base/cons/copy_neg.cc	10 Dec 2003 00:14:45 -0000
*************** void test02()
*** 41,45 ****
    test_base io2 = io1; 
  }
  // { dg-error "within this context" "" { target *-*-* } 41 } 
! // { dg-error "is private" "" { target *-*-* } 743 } 
  // { dg-error "copy constructor" "" { target *-*-* } 0 } 
--- 41,45 ----
    test_base io2 = io1; 
  }
  // { dg-error "within this context" "" { target *-*-* } 41 } 
! // { dg-error "is private" "" { target *-*-* } 742 } 
  // { dg-error "copy constructor" "" { target *-*-* } 0 } 


-- 


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