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boost_shared_ptr.h: Avoid unnecessary memory barriers in _S_atomic case. 

2007-11-06  Jonathan Wakely  <jwakely.gcc@gmail.com>

	* include/tr1_impl/boost_shared_ptr.h: Avoid unnecessary memory
	barriers in _S_atomic case.

From-SVN: r129927
This commit is contained in:
Jonathan Wakely 2007-11-06 14:28:28 +00:00 committed by Jonathan Wakely
parent 0eb7e7aa01
commit 3de36a09ac
2 changed files with 42 additions and 16 deletions
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5
libstdc++-v3/ChangeLog
View File

@ -1,3 +1,8 @@
2007-11-06 Jonathan Wakely <jwakely.gcc@gmail.com>
* include/tr1_impl/boost_shared_ptr.h: Avoid unnecessary memory
barriers in _S_atomic case.
2007-11-05 Chris Jefferson <chris@bubblescope.net>
Paolo Carlini <pcarlini@suse.de>

53
libstdc++-v3/include/tr1_impl/boost_shared_ptr.h
View File

@ -94,12 +94,22 @@ _GLIBCXX_BEGIN_NAMESPACE_TR1
// Empty helper class except when the template argument is _S_mutex.
template<_Lock_policy _Lp>
class _Mutex_base
{ };
{
protected:
// The atomic policy uses fully-fenced builtins, single doesn't care.
enum { _S_need_barriers = 0 };
};
template<>
class _Mutex_base<_S_mutex>
: public __gnu_cxx::__mutex
{ };
{
protected:
// This policy is used when atomic builtins are not available.
// The replacement atomic operations might not have the necessary
// memory barriers.
enum { _S_need_barriers = 1 };
};
template<_Lock_policy _Lp = __default_lock_policy>
class _Sp_counted_base
@ -136,14 +146,19 @@ _GLIBCXX_BEGIN_NAMESPACE_TR1
void
_M_release() // nothrow
{
if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count,
-1) == 1)
if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, -1) == 1)
{
_M_dispose();
#ifdef __GTHREADS
_GLIBCXX_READ_MEM_BARRIER;
_GLIBCXX_WRITE_MEM_BARRIER;
#endif
// There must be a memory barrier between dispose() and destroy()
// to ensure that the effects of dispose() are observed in the
// thread that runs destroy().
// See http://gcc.gnu.org/ml/libstdc++/2005-11/msg00136.html
if (_Mutex_base<_Lp>::_S_need_barriers)
{
_GLIBCXX_READ_MEM_BARRIER;
_GLIBCXX_WRITE_MEM_BARRIER;
}
if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count,
-1) == 1)
_M_destroy();
@ -159,18 +174,25 @@ _GLIBCXX_BEGIN_NAMESPACE_TR1
{
if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count, -1) == 1)
{
#ifdef __GTHREADS
_GLIBCXX_READ_MEM_BARRIER;
_GLIBCXX_WRITE_MEM_BARRIER;
#endif
if (_Mutex_base<_Lp>::_S_need_barriers)
{
// See _M_release(),
// destroy() must observe results of dispose()
_GLIBCXX_READ_MEM_BARRIER;
_GLIBCXX_WRITE_MEM_BARRIER;
}
_M_destroy();
}
}
long
_M_get_use_count() const // nothrow
{ return _M_use_count; } // XXX is this MT safe?
{
// No memory barrier is used here so there is no synchronization
// with other threads.
return const_cast<const volatile _Atomic_word&>(_M_use_count);
}
private:
_Sp_counted_base(_Sp_counted_base const&);
_Sp_counted_base& operator=(_Sp_counted_base const&);
@ -525,7 +547,7 @@ _GLIBCXX_BEGIN_NAMESPACE_TR1
}
//
// Requirements: _Deleter' copy constructor and destructor must not throw
// Requirements: _Deleter's copy constructor and destructor must not throw
//
// __shared_ptr will release __p by calling __d(__p)
//
@ -552,7 +574,6 @@ _GLIBCXX_BEGIN_NAMESPACE_TR1
* with @a __r.
* @param __r A %__shared_ptr.
* @post get() == __r.get() && use_count() == __r.use_count()
* @throw std::bad_alloc, in which case
*/
template<typename _Tp1>
__shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r)