set_map_service( const std::shared_ptr request, std::shared_ptr response); void generate_path_service( const std::shared_ptr request, std::shared_ptr response); bool set_costmap(const std_msgs::msg::UInt8MultiArray& costmap); Path generate_global_path(Position set_map_service( const std::shared_ptr request, std::shared_ptr response); void generate_path_service( const std::shared_ptr

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danielanderson.net What we’ll learn today • How shared_ptr is implemented under the hood • Atomics and concurrency patterns • How existing atomic<shared_ptr> are implemented (the split reference count technique) 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 under the the hood • Atomics and concurrency patterns • How existing atomic<shared_ptr> are implemented (the split reference count technique) • Deferred reclamation, i.e., garbage collection in C++ Some assumed

www.ModernesCpp.netSmart Pointer A First Overview std::unique_ptr – Exclusive Ownership std::shared_ptr – Shared Ownership std::weak_ptr – Break of Cyclic References Performance Concurrency Function Arguments and Return ValuesSmart Pointer A First Overview std::unique_ptr – Exclusive Ownership std::shared_ptr – Shared Ownership std::weak_ptr – Break of Cyclic References Performance Concurrency Function C++11 ▪ Owns the resource exclusively ▪ Can not be copied ▪ Deals with non-copy objects std::shared_ptr C++11 ▪ Shares a resource ▪ Supports an reference counter to the shared resource and manages it

Reference Counting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 5.2 std::shared_ptr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 5.3 std::unique_ptr mers no longer need to care about manually releasing memory. These smart pointers include std::shared_ptr/std::unique_ptr/std::weak_ptr, which need to include the header file . Note: The reference of resources. 57 5.2 std::shared_ptr CHAPTER 05 SMART POINTERS AND MEMORY MANAGEMENT 5.2 std::shared_ptr std::shared_ptr is a smart pointer that records how many shared_ptr points to an object, elimi-

interface name using LoaderType = pluginlib::ClassLoader std::shared_ptr loader = std::make_shared("package_name"); // In ROS world plugin name which is declared in the XML file. Maybe we send the derived class name? std::shared_ptr motion_planner = loader->createUniqueInstance("simple_motion_planner"); the interface name using LoaderType = pluginlib::ClassLoader std::shared_ptr loader = std::make_shared("package_name"); // In ROS world

*o << " prints 9\n"; • views::nullable — Extra safety for maybe-like types — std::optional, shared_ptr, raw ptrs, result of find (?)© 2018 Bloomberg Finance L.P. All rights reserved. How does this *o << " prints 9\n"; • views::nullable — Extra safety for maybe-like types — std::optional, shared_ptr, raw ptrs, result of find (?) • Give us the basis to implement anything! p1255: A view of 0 out; 15: } and_then • views::nullable — Extra safety for maybe-like types — std::optional, shared_ptr, raw ptrs, result of find (?) p1255: A view of 0 or 1 elements: views::maybe by Steve Downey

save a second or two Speaker notesORIGINAL NODE SORTING CODE struct Node; using NodePtr = std::shared_ptr; struct Prefab { uint64_t GetId() const; std::vector nodes_; }; struct Node primitive • Result: 100% CPU usage for many minutes SpinLock data_save_lock; void Process(std::shared_ptr data) { data->Processing(); { SpinLockGuard guard(data_save_lock); data->SaveFile(); std::mutex data_save_lock; std::lock_guard guard(data_save_lock); 1 2 void Process(std::shared_ptr data) 3 { 4 data->Processing(); 5 6 { 7 8 data->SaveFile(); 9 } 10 } 11 39To verify

std::atomicshared_ptr> g_config; void setDefaultHostname(const std::string& value) { std::shared_ptr blue = g_config.load(); do { std::shared_ptr std::map; std::atomicshared_ptr> g_config; // ... std::shared_ptr getDefaultHostname() { std::shared_ptr blue = g_config.load(); load(); const std::string& value = blue.at("default.hostname"); return std::shared_ptr(std::move(blue), &value); } 50 “Aliasing constructor” alert! The blue ConfigMap will stay

template> class unique_ptr {...};The custom deleter for shared_ptr and unique_ptr are di�erent We’re used to this construct of a smart pointer: But this will cause not delete Where D is a (dangerous!) custom deleter de�ned by: shared_ptr my_ptr = rhs; unique_ptr my_uniqueptr = rhs; shared_ptr my_sharedptr(ref,D); template struct no_deleter { operator operator () (T* ptr) { // do nothing } }The custom deleter for shared_ptr and unique_ptr are di�erent We’re used to this construct of a smart pointer: But this will cause a ‘delete’ when the scope

and only one decrement must “take credit” for zeroing the counter29 Benchmarks • My atomic<shared_ptr> implementation using the wait-free counter versus the lock-free counter. This affects the performance performance of the load operation. • Benchmark #1: 𝒑 threads loading from an atomic<shared_ptr> Daniel Anderson -- danielanderson.net 𝟏% 𝟓𝟎% 𝟗𝟗% 𝑝 = 1 21n 24.8n 32.7n 𝑝 = 28 217n 1.75u 13 13.3u Lock Free Counter Wait Free Counter Load Latency Load Latency30 Benchmarks • My atomic<shared_ptr> implementation using the wait-free counter versus the lock-free counter. This affects the performance