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std::kill_dependency(3) C++ Standard Libary std::kill_dependency(3) NAME std::kill_dependency - std::kill_dependency Synopsis Defined in header <atomic> template< class T > (since C++11) T kill_dependency( T y ) noexcept; Informs the compiler that the dependency tree started by an std::memory_order_consume atomic load operation does not extend past the return value of std::kill_dependency; that is, the argument does not carry a dependency into the return value. This may be used to avoid unnecessary std::memory_order_acquire fences when the dependency chain leaves function scope (and the function does not have the [[carries_dependency]] attribute) Parameters y - the expression whose return value is to be removed from a depen- dency tree Return value Returns y, no longer a part of a dependency tree. Examples file1.cpp: struct foo { int* a; int* b; }; std::atomic<struct foo*> foo_head[10]; int foo_array[10][10]; // consume operation starts a dependency chain, which escapes this function [[carries_dependency]] struct foo* f(int i) { return foo_head[i].load(memory_order_consume); } // the dependency chain enters this function through the right parame- ter // and is killed before the function ends (so no extra acquire opera- tion takes place) int g(int* x, int* y [[carries_dependency]]) { return std::kill_dependency(foo_array[*x][*y]); } file2.cpp: [[carries_dependency]] struct foo* f(int i); int g(int* x, int* y [[carries_dependency]]); int c = 3; void h(int i) { struct foo* p; p = f(i); // dependency chain started inside f continues into p without undue acquire do_something_with(g(&c, p->a)); // p->b is not brought in from the cache do_something_with(g(p->a, &c)); // left argument does not have the carries_dependency // attribute: memory acquire fence may be issued // p->b becomes visible before g() is entered } See also memory_order defines memory ordering constraints for the given atomic operation (C++11) (enum) http://cppreference.com 2022.07.31 std::kill_dependency(3)
NAME | Synopsis | Parameters | Return value | Examples | See also
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