does and what it is used for • You’ve heard of shared_ptr Things we won’t cover • Alias pointers, weak pointers4 Daniel Anderson -- danielanderson.net What we’ll learn today • How shared_ptr is implemented does and what it is used for • You’ve heard of shared_ptr Things we won’t cover • Alias pointers, weak pointers5 Daniel Anderson -- danielanderson.net Why is this important?6 Daniel Anderson -- _ptr>16 Daniel Anderson -- danielanderson.net std::atomic • Atomic shared pointers were introduced to answer the age-old question…17 Daniel Anderson -- danielanderson.net std

Synchronous Reclamation Beyond Concurrency TS2 – Maged Michael Protector Remover / Reclaimer Hazard pointers protect access to objects that may be removed concurrently. SAFE RECLAMATION Concurrency TS2 Essential objects template class hazard_pointer_obj_base { void retire() noexcept; }; Hazard pointers class hazard_pointer { template T* protect(const std::atomic& src) noexcept; Maged Michael See N4895 (wg21.link/n4895) for working draft of Concurrency TS2 Example Using Hazard Pointers class Foo : public hazard_pointer_obj_base { /* Foo members */ }; Result read_and_use(std::atomic&

dynamic_cast, typeid  allocations  constexpr string & vector  Concurrency Changes  Atomic Smart Pointers  Joining & Cancellable Threads  The C++20 Synchronization Library  Semaphores, efficient atomic GitHub” -- Stephan T. Lavavej Tuesday, September 15 • 13:30Concurrency Changes35 Atomic Smart Pointers  Is shared_ptr thread safe?  Yes: control block manipulation thread safe  guarantees object Might use mutex internally  Global non-member atomic operations are deprecated36 Atomic Smart Pointers template class concurrent_stack { struct Node { T t; shared_ptr next; };

stealing Software Queue Issues Producer Enqueue Software Dequeue Software Head and Tail pointers Dequeue Software Dequeue Software Enqueue Software Producer Consumer Consumer Consumer Memory/Cache latency • CPU cycles latency DLB ： Dynamic Load Balance DLB Enqueue Logic Head and Tail pointers Dequeue Logic & Load Balancer Producer Producer Consumer Consumer Consumer • No Synchronization

libraries with API:  declare_reachable()  undeclare_reachable()  declare_no_pointers()  undeclare_no_pointers()  get_pointer_safety()  enum pointer_safety  Available since C++11  Not aware