ywkaras commented on a change in pull request #7362:
URL: https://github.com/apache/trafficserver/pull/7362#discussion_r534617265
##########
File path: src/tscore/ink_queue.cc
##########
@@ -66,6 +67,139 @@
#define DEADBEEF
#endif
+namespace
+{
+// Atomic stack, implemented as a linked list. The link is stored at the
offset (given by the base class
+// member function link_offset() ) within each stack element. The stack is
empty when the head pointer is null.
+//
+template <class Base> class AtomicStack_ : private Base
+{
+public:
+ template <typename... Args>
+ AtomicStack_(std::atomic<void *> &head, Args &&... args) :
Base(std::forward<Args>(args)...), _head(head)
+ {
+ }
+
+ // Return reference to "next" pointer within a stack element.
+ //
+ void *&
+ link(void *elem)
+ {
+ return *reinterpret_cast<void **>(static_cast<char *>(elem) +
Base::link_offset());
+ }
+
+ // Splice this stack to the tail of another stack (whose head and tail is
given by the parameters).
+ // Returns previous head.
+ //
+ void *
+ splice_to_top(void *other_head, void *other_tail)
+ {
+ void *curr_head = _head;
+
+ do {
+ link(other_tail) = curr_head;
+
+ } while (!_head.compare_exchange_weak(curr_head, other_head));
+
+ return curr_head;
+ }
+
+ // Returns previous head.
+ //
+ void *
+ push(void *elem)
+ {
+ return splice_to_top(elem, elem);
+ }
+
+ template <bool All_elements = false>
+ void *
+ pop()
+ {
+ void *curr_head = _head, *new_head;
+
+ do {
+ if (!curr_head) {
+ // Stack is empty.
+ //
+ return nullptr;
+ }
+
+ new_head = All_elements ? nullptr : link(curr_head);
+
+ } while (!_head.compare_exchange_weak(curr_head, new_head));
+
+ return curr_head;
+ }
+
+ // WARNING: This is not safe, unless no other thread is popping or removing.
+ //
+ bool
+ remove(void *item)
+ {
+ void *p = item;
+ void *p2 = link(item);
+
+ if (_head.compare_exchange_strong(p, p2)) {
+ // Item was at the top of the stack.
+ //
+ return true;
+ }
+ if (p) {
+ p2 = link(p);
+
+ while (p2 != item) {
+ if (nullptr == p2) {
+ // Item not in stack.
+ //
+ return false;
+ }
+ p = p2;
+ p2 = link(p2);
+ }
+ link(p) = link(p2);
+ return true;
+ }
+ // Stack is empty.
+ //
+ return false;
+ }
+
+private:
+ std::atomic<void *> &_head;
+};
+
+class AtomicStackBaseNoOffset
+{
+protected:
+ static constexpr size_t
+ link_offset()
+ {
+ return 0;
+ }
+};
+
+using AtomicStackNoOffset = AtomicStack_<AtomicStackBaseNoOffset>;
+
+class AtomicStackBaseWithOffset
+{
+protected:
+ AtomicStackBaseWithOffset(size_t offset) : _link_offset(offset) {}
+
+ size_t
+ link_offset() const
+ {
+ return (_link_offset);
Review comment:
remove paretheses
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