diff options
Diffstat (limited to 'libstdc++-v3/include/std/latch')
| -rw-r--r-- | libstdc++-v3/include/std/latch | 26 |
1 files changed, 22 insertions, 4 deletions
diff --git a/libstdc++-v3/include/std/latch b/libstdc++-v3/include/std/latch index dc147c2..9504df0 100644 --- a/libstdc++-v3/include/std/latch +++ b/libstdc++-v3/include/std/latch @@ -89,15 +89,33 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION _GLIBCXX_ALWAYS_INLINE void wait() const noexcept { - auto const __pred = [this] { return this->try_wait(); }; - std::__atomic_wait_address(&_M_counter, __pred); + auto const __vfn = [this] { + return __atomic_impl::load(&_M_counter, memory_order::acquire); + }; + auto const __pred = [](__detail::__platform_wait_t __v) { + return __v == 0; + }; + std::__atomic_wait_address(&_M_counter, __pred, __vfn); } _GLIBCXX_ALWAYS_INLINE void arrive_and_wait(ptrdiff_t __update = 1) noexcept { - count_down(__update); - wait(); + // The standard specifies this functions as count_down(update); wait(); + // but we combine those two calls into one and avoid the wait() if we + // know the counter reached zero. + + __glibcxx_assert(__update >= 0 && __update <= max()); + // Use acq_rel here because an omitted wait() would have used acquire: + auto const __old = __atomic_impl::fetch_sub(&_M_counter, __update, + memory_order::acq_rel); + if (std::cmp_equal(__old, __update)) + __atomic_impl::notify_all(&_M_counter); + else + { + __glibcxx_assert(std::cmp_less(__update, __old)); + wait(); + } } private: |