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
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2007-11-06 Jonathan Wakely <jwakely.gcc@gmail.com>
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* include/tr1_impl/boost_shared_ptr.h: Avoid unnecessary memory
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barriers in _S_atomic case.
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2007-11-05 Chris Jefferson <chris@bubblescope.net>
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Paolo Carlini <pcarlini@suse.de>
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@ -94,12 +94,22 @@ _GLIBCXX_BEGIN_NAMESPACE_TR1
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// Empty helper class except when the template argument is _S_mutex.
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template<_Lock_policy _Lp>
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class _Mutex_base
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{ };
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{
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protected:
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// The atomic policy uses fully-fenced builtins, single doesn't care.
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enum { _S_need_barriers = 0 };
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};
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template<>
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class _Mutex_base<_S_mutex>
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: public __gnu_cxx::__mutex
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{ };
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{
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protected:
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// This policy is used when atomic builtins are not available.
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// The replacement atomic operations might not have the necessary
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// memory barriers.
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enum { _S_need_barriers = 1 };
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};
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template<_Lock_policy _Lp = __default_lock_policy>
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class _Sp_counted_base
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@ -136,14 +146,19 @@ _GLIBCXX_BEGIN_NAMESPACE_TR1
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void
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_M_release() // nothrow
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{
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if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count,
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-1) == 1)
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if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, -1) == 1)
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{
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_M_dispose();
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#ifdef __GTHREADS
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_GLIBCXX_READ_MEM_BARRIER;
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_GLIBCXX_WRITE_MEM_BARRIER;
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#endif
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// There must be a memory barrier between dispose() and destroy()
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// to ensure that the effects of dispose() are observed in the
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// thread that runs destroy().
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// See http://gcc.gnu.org/ml/libstdc++/2005-11/msg00136.html
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if (_Mutex_base<_Lp>::_S_need_barriers)
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{
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_GLIBCXX_READ_MEM_BARRIER;
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_GLIBCXX_WRITE_MEM_BARRIER;
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}
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if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count,
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-1) == 1)
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_M_destroy();
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@ -159,17 +174,24 @@ _GLIBCXX_BEGIN_NAMESPACE_TR1
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{
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if (__gnu_cxx::__exchange_and_add_dispatch(&_M_weak_count, -1) == 1)
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{
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#ifdef __GTHREADS
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_GLIBCXX_READ_MEM_BARRIER;
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_GLIBCXX_WRITE_MEM_BARRIER;
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#endif
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if (_Mutex_base<_Lp>::_S_need_barriers)
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{
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// See _M_release(),
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// destroy() must observe results of dispose()
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_GLIBCXX_READ_MEM_BARRIER;
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_GLIBCXX_WRITE_MEM_BARRIER;
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}
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_M_destroy();
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}
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}
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long
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_M_get_use_count() const // nothrow
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{ return _M_use_count; } // XXX is this MT safe?
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{
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// No memory barrier is used here so there is no synchronization
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// with other threads.
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return const_cast<const volatile _Atomic_word&>(_M_use_count);
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}
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private:
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_Sp_counted_base(_Sp_counted_base const&);
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@ -525,7 +547,7 @@ _GLIBCXX_BEGIN_NAMESPACE_TR1
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}
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//
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// Requirements: _Deleter' copy constructor and destructor must not throw
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// Requirements: _Deleter's copy constructor and destructor must not throw
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//
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// __shared_ptr will release __p by calling __d(__p)
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//
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@ -552,7 +574,6 @@ _GLIBCXX_BEGIN_NAMESPACE_TR1
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* with @a __r.
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* @param __r A %__shared_ptr.
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* @post get() == __r.get() && use_count() == __r.use_count()
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* @throw std::bad_alloc, in which case
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*/
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template<typename _Tp1>
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__shared_ptr(const __shared_ptr<_Tp1, _Lp>& __r)
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