>::type storage;staticstd::atomic<int> flag;while(flag <2) {// all threads spin until the object is properly initializedintexpected =0;if(flag.compare_exchange_weak(expected,1)) {// only one thread succeeds at the compare_exchange.try{ ::new(&storage) my_type; }catch(...) {// I...
例子 usestd::sync::atomic::{AtomicPtr, Ordering};letsome_ptr = AtomicPtr::new(&mut5);letnew = &mut10;letmutold = some_ptr.load(Ordering::Relaxed);loop{matchsome_ptr.compare_exchange_weak(old, new, Ordering::SeqCst, Ordering::Relaxed) {Ok(_) =>break,Err(x) => old = x...
如果操作在循环中,使用compare_exchange_weak通常更好。 如果是单次操作,使用compare_exchange更合适。 在某些平台上,这两个操作可能没有性能差异,但compare_exchange_weak的行为仍然可能不同。 这种区别的存在是因为在某些 CPU 架构上,允许虚假失败可以生成更高效的机器码。比如在 ARM 架构上,compare_exchange_weak可...
compare_exchange_weak函数直接比较所包含值的物理内容，这可能导致使用(如果底层类型有填充位、陷阱值或相...
该函数直接比较原子对象所封装的值与expect的物理内容,在某些情况下,对象的比较操作在使用 operator==() 判断时相等,但 compare_exchange_weak 判断时却可能失败,因为对象底层的物理内容中可能存在位对齐或其他逻辑表示相同但是物理表示不同的值(比如 true 和 5,它们在逻辑上都表示"真",但在物理上两者的表示并不相...
atomic compare_exchange_weak函数 compare_exchange_weak/compare_exchange_strong (是著名的CAS(compare and set))。 参数传入期待值与新值,通过比较当前值与期待值的情况进行区别改变。 a.compare_exchange_weak(b,c)其中a是当前值,b期望值,c新值 a==b时:函数返回真,并把c赋值给a...
(2)(自C11以来)_Bool atomic_compare_exchange_strong_explicit(volatile A * obj,C * expected,C desired,memory_order succ,memory_order fail);(3)(自C11以来)_Bool atomic_compare_exchange_weak_explicit(volatile A * obj,C * expected,C desired,memory_order succ,memory_order fail);(4)(自C11...
Prototypes boolA::compare_exchange_weak(C&expected,Cdesired, memory_ordersuccess, memory_orderfailure) volatile noexcept; boolA::compare_exchange_weak(C&expected,Cdesired, memory_ordersuccess, memory_orderfailure) noexcept; boolA::compare_exchange_weak(C&expected,Cdesired, memory_orderorder= memory_or...
bool compare_exchange_weak( Ty& Exp, Ty Value, memory_order Order1, memory_order Order2 ) volatile _NOEXCEPT; bool compare_exchange_weak( Ty& Exp, Ty Value, memory_order Order1, memory_order Order2 ) _NOEXCEPT; bool compare_exchange_weak( Ty& Exp, Ty Value, memory_order Order1 = me...
bool atomic_compare_exchange_weak (volatile A* obj, T* expected, T val) noexcept; bool atomic_compare_exchange_weak (A* obj, T* expected, T val) noexcept; Compare and exchange contained value (weak) Compares the contents of the value contained inobjwith that ofexpected: ...