template< class T >
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).
Simply returns y. This function template is deprecated.
(since C++26) [edit] Parameters y - the expression whose return value is to be removed from a dependency tree [edit] Return valueReturns y, no longer a part of a dependency tree(until C++26).
[edit] Examples [edit] file1.cpp:struct Foo
{
int* a;
int* b;
};
std::atomic<Foo*> foo_head[10];
int foo_array[10][10];
// consume operation starts a dependency chain, which escapes this function
[[carries_dependency]] Foo* f(int i)
{
return foo_head[i].load(memory_order_consume);
}
// the dependency chain enters this function through the right parameter and is
// killed before the function ends (so no extra acquire operation takes place)
int g(int* x, int* y [[carries_dependency]])
{
return std::kill_dependency(foo_array[*x][*y]);
}[edit] file2.cpp:
[[carries_dependency]] struct Foo* f(int i);
int g(int* x, int* y [[carries_dependency]]);
int c = 3;
void h(int i)
{
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
}[edit] See also
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