@@ -42,7 +42,28 @@ class sequence {
4242 T* head_;
4343};
4444
45- template <typename T,typename Mutex = std::mutex>
45+ class spin_lock {
46+ public:
47+ void lock ()noexcept {
48+ while (flag_.test_and_set (std::memory_order_acquire)) {
49+ #if defined(__cpp_lib_atomic_wait) && __cpp_lib_atomic_wait >= 201907L
50+ flag_.wait (true , std::memory_order_relaxed);
51+ #endif
52+ }
53+ }
54+
55+ void unlock ()noexcept {
56+ flag_.clear (std::memory_order_release);
57+ #if defined(__cpp_lib_atomic_wait) && __cpp_lib_atomic_wait >= 201907L
58+ flag_.notify_one ();
59+ #endif
60+ }
61+
62+ private:
63+ std::atomic_flag flag_ = ATOMIC_FLAG_INIT;
64+ };
65+
66+ template <typename T,typename Mutex = spin_lock>
4667class queue {
4768public:
4869 sequence<T>extract () {
@@ -113,7 +134,7 @@ class mpsc_stack {
113134
114135 sequence<T>extract ()noexcept {
115136do {
116- T* top = head_.load ();
137+ T* top = head_.load (std::memory_order_relaxed );
117138
118139if (top ==nullptr ) {
119140return sequence<T>{nullptr };
@@ -126,7 +147,7 @@ class mpsc_stack {
126147
127148void push (T*const node)noexcept {
128149do {
129- T* top = head_.load ();
150+ T* top = head_.load (std::memory_order_relaxed );
130151 node->next = top;
131152if (head_.compare_exchange_weak (top, node)) {
132153return ;
@@ -142,17 +163,17 @@ class mpsc_stack {
142163
143164 T*pop ()noexcept {
144165do {
145- T* top = head_.load ();
146-
166+ T* top = head_.load (std::memory_order_consume );
167+ // Check the stack is empty.
147168if (top ==nullptr ) {
148169return nullptr ;
149- }else {
150- T* next = top->next ;
170+ }
151171
152- if (head_.compare_exchange_weak (top, next)) {
153- top->next =nullptr ;
154- return top;
155- }
172+ T* next = top->next ;
173+ // Pop the item.
174+ if (head_.compare_exchange_weak (top, next)) {
175+ top->next =nullptr ;
176+ return top;
156177 }
157178 }while (true );
158179 }