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libstdc++: Implement std::atomic<T*>::compare_exchange_weak

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For some reason r170217 didn't add compare_exchange_weak to the
__atomic_base<T*> partial specialization, and so weak compare exchange
operations on pointers use compare_exchange_strong instead.

This adds __atomic_base<T*>::compare_exchange_weak and then uses it in
std::atomic<T*>::compare_exchange_weak.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

libstdc++-v3/ChangeLog:

	* include/bits/atomic_base.h (__atomic_base<P*>::compare_exchange_weak):
	Add new functions.
	* include/std/atomic (atomic<T*>::compare_exchange_weak): Use
	it.
This commit is contained in:
Jonathan Wakely 2021-09-02 16:47:31 +01:00
parent 892400f1f2
commit 89cf858571
2 changed files with 24 additions and 2 deletions
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22
libstdc++-v3/include/bits/atomic_base.h
View File

@ -846,6 +846,28 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return __atomic_exchange_n(&_M_p, __p, int(__m));
}
_GLIBCXX_ALWAYS_INLINE bool
compare_exchange_weak(__pointer_type& __p1, __pointer_type __p2,
memory_order __m1,
memory_order __m2) noexcept
{
__glibcxx_assert(__is_valid_cmpexch_failure_order(__m2));
return __atomic_compare_exchange_n(&_M_p, &__p1, __p2, 1,
int(__m1), int(__m2));
}
_GLIBCXX_ALWAYS_INLINE bool
compare_exchange_weak(__pointer_type& __p1, __pointer_type __p2,
memory_order __m1,
memory_order __m2) volatile noexcept
{
__glibcxx_assert(__is_valid_cmpexch_failure_order(__m2));
return __atomic_compare_exchange_n(&_M_p, &__p1, __p2, 1,
int(__m1), int(__m2));
}
_GLIBCXX_ALWAYS_INLINE bool
compare_exchange_strong(__pointer_type& __p1, __pointer_type __p2,
memory_order __m1,

4
libstdc++-v3/include/std/atomic
View File

@ -595,13 +595,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
bool
compare_exchange_weak(__pointer_type& __p1, __pointer_type __p2,
memory_order __m1, memory_order __m2) noexcept
{ return _M_b.compare_exchange_strong(__p1, __p2, __m1, __m2); }
{ return _M_b.compare_exchange_weak(__p1, __p2, __m1, __m2); }
bool
compare_exchange_weak(__pointer_type& __p1, __pointer_type __p2,
memory_order __m1,
memory_order __m2) volatile noexcept
{ return _M_b.compare_exchange_strong(__p1, __p2, __m1, __m2); }
{ return _M_b.compare_exchange_weak(__p1, __p2, __m1, __m2); }
bool
compare_exchange_weak(__pointer_type& __p1, __pointer_type __p2,