hazard pointers: Eliminate thread local lists of retired objects

Summary:
Remove hazptr_priv, the thread-local list of retired objects.

Non-cohort retired objects are pushed directly into the domain.

Reviewed By: davidtgoldblatt

Differential Revision: D30806863

fbshipit-source-id: 526c90f5a198b4e42a55062cb7344e5286bf28fd

folly/synchronization/Hazptr-fwd.h

@@ -119,14 +119,6 @@ class hazptr_tc;
 template <template <typename> class Atom = std::atomic>
 hazptr_tc<Atom>& hazptr_tc_tls();
 
-/** hazptr_priv */
-template <template <typename> class Atom = std::atomic>
-class hazptr_priv;
-
-/** hazptr_priv_tls */
-template <template <typename> class Atom = std::atomic>
-hazptr_priv<Atom>& hazptr_priv_tls();
-
 ///
 /// Hazard pointer domain
 /// Defined in HazptrDomain.h

folly/synchronization/HazptrDomain.h

@@ -583,19 +583,6 @@ class hazptr_domain {
   }
 
   void relaxed_cleanup() noexcept {
-#if FOLLY_HAZPTR_THR_LOCAL
-    hazptr_obj<Atom>* h = nullptr;
-    hazptr_obj<Atom>* t = nullptr;
-    for (hazptr_priv<Atom>& priv :
-         hazptr_priv_singleton<Atom>::accessAllThreads()) {
-      priv.collect(h, t);
-    }
-    if (h) {
-      DCHECK(t);
-      hazptr_obj_list<Atom> l(h, t, 0);
-      push_retired(l);
-    }
-#endif
     rcount_.store(0, std::memory_order_release);
     bulk_reclaim(true);
   }
@@ -654,11 +641,6 @@ class hazptr_domain {
       }
       obj = next;
     }
-#if FOLLY_HAZPTR_THR_LOCAL
-    if (!shutdown_) {
-      hazptr_priv_tls<Atom>().push_all_to_domain(false);
-    }
-#endif
     bool done = ((children.count() == 0) && (retired() == nullptr));
     matched.splice(children);
     if (matched.count() > 0) {

folly/synchronization/HazptrObj.h

@@ -91,7 +91,6 @@ class hazptr_obj {
   template <typename, template <typename> class, typename>
   friend class hazptr_obj_base_linked;
   friend class hazptr_obj_list<Atom>;
-  friend class hazptr_priv<Atom>;
   friend class hazptr_detail::linked_list<Obj>;
   friend class hazptr_detail::shared_head_only_list<Obj, Atom>;
   friend class hazptr_detail::shared_head_tail_list<Obj, Atom>;
@@ -150,7 +149,6 @@ class hazptr_obj {
   template <typename, template <typename> class, typename>
   friend class hazptr_obj_base_refcounted;
   friend class hazptr_obj_cohort<Atom>;
-  friend class hazptr_priv<Atom>;
 
   Obj* next() const noexcept { return next_; }
 
@@ -178,12 +176,6 @@ class hazptr_obj {
   }
 
   void push_to_retired(hazptr_domain<Atom>& domain) {
-#if FOLLY_HAZPTR_THR_LOCAL
-    if (&domain == &default_hazptr_domain<Atom>() && !domain.shutdown_) {
-      hazptr_priv_tls<Atom>().push(this);
-      return;
-    }
-#endif
     hazptr_obj_list<Atom> l(this);
     hazptr_domain_push_retired(l, true, domain);
   }

folly/synchronization/HazptrThrLocal.h

@@ -160,151 +160,6 @@ FOLLY_ALWAYS_INLINE hazptr_tc<Atom>& hazptr_tc_tls() {
   return folly::SingletonThreadLocal<hazptr_tc<Atom>, hazptr_tc_tls_tag>::get();
 }
 
-/**
- *  hazptr_priv
- *
- *  Per-thread list of retired objects to be pushed in bulk to domain.
- */
-template <template <typename> class Atom>
-class hazptr_priv {
-  static constexpr int kThreshold = 20;
-
-  Atom<hazptr_obj<Atom>*> head_;
-  Atom<hazptr_obj<Atom>*> tail_;
-  int rcount_;
-  bool in_dtor_;
-
- public:
-  hazptr_priv() : head_(nullptr), tail_(nullptr), rcount_(0), in_dtor_(false) {}
-
-  ~hazptr_priv() {
-    in_dtor_ = true;
-    if (!empty()) {
-      push_all_to_domain(false);
-    }
-  }
-
- private:
-  friend class hazptr_domain<Atom>;
-  friend class hazptr_obj<Atom>;
-
-  bool empty() const noexcept { return head() == nullptr; }
-
-  void push(hazptr_obj<Atom>* obj) {
-    DCHECK(!in_dtor_);
-    push_in_priv_list(obj);
-  }
-
-  void push_in_priv_list(hazptr_obj<Atom>* obj) {
-    while (true) {
-      if (tail()) {
-        if (push_in_non_empty_list(obj)) {
-          break;
-        }
-      } else {
-        if (push_in_empty_list(obj)) {
-          break;
-        }
-      }
-    }
-    if (++rcount_ >= kThreshold) {
-      push_all_to_domain(true);
-    }
-  }
-
-  void push_all_to_domain(bool check_to_reclaim) {
-    hazptr_obj<Atom>* h = nullptr;
-    hazptr_obj<Atom>* t = nullptr;
-    collect(h, t);
-    if (h) {
-      DCHECK(t);
-      hazptr_obj_list<Atom> l(h, t, rcount_);
-      hazptr_domain_push_retired<Atom>(l, check_to_reclaim);
-      rcount_ = 0;
-    }
-  }
-
-  void collect(
-      hazptr_obj<Atom>*& colHead, hazptr_obj<Atom>*& colTail) noexcept {
-    // This function doesn't change rcount_.
-    // The value rcount_ is accurate excluding the effects of calling collect().
-    auto h = exchange_head();
-    if (h) {
-      auto t = exchange_tail();
-      DCHECK(t);
-      if (colTail) {
-        colTail->set_next(h);
-      } else {
-        colHead = h;
-      }
-      colTail = t;
-    }
-  }
-
-  hazptr_obj<Atom>* head() const noexcept {
-    return head_.load(std::memory_order_acquire);
-  }
-
-  hazptr_obj<Atom>* tail() const noexcept {
-    return tail_.load(std::memory_order_acquire);
-  }
-
-  void set_head(hazptr_obj<Atom>* obj) noexcept {
-    head_.store(obj, std::memory_order_release);
-  }
-
-  bool cas_head(hazptr_obj<Atom>* expected, hazptr_obj<Atom>* obj) noexcept {
-    return head_.compare_exchange_weak(
-        expected, obj, std::memory_order_acq_rel, std::memory_order_relaxed);
-  }
-
-  bool cas_tail(hazptr_obj<Atom>* expected, hazptr_obj<Atom>* obj) noexcept {
-    return tail_.compare_exchange_weak(
-        expected, obj, std::memory_order_acq_rel, std::memory_order_relaxed);
-  }
-
-  hazptr_obj<Atom>* exchange_head() noexcept {
-    return head_.exchange(nullptr, std::memory_order_acq_rel);
-  }
-
-  hazptr_obj<Atom>* exchange_tail() noexcept {
-    return tail_.exchange(nullptr, std::memory_order_acq_rel);
-  }
-
-  bool push_in_non_empty_list(hazptr_obj<Atom>* obj) noexcept {
-    auto h = head();
-    if (h) {
-      obj->set_next(h);
-      if (cas_head(h, obj)) {
-        return true;
-      }
-    }
-    return false;
-  }
-
-  bool push_in_empty_list(hazptr_obj<Atom>* obj) noexcept {
-    hazptr_obj<Atom>* t = nullptr;
-    obj->set_next(nullptr);
-    if (cas_tail(t, obj)) {
-      set_head(obj);
-      return true;
-    }
-    return false;
-  }
-}; // hazptr_priv
-
-/** hazptr_priv_tls */
-struct HazptrTag {};
-
-template <template <typename> class Atom>
-using hazptr_priv_singleton =
-    folly::SingletonThreadLocal<hazptr_priv<Atom>, HazptrTag>;
-
-template <template <typename> class Atom>
-FOLLY_ALWAYS_INLINE hazptr_priv<Atom>& hazptr_priv_tls() {
-  return hazptr_priv_singleton<Atom>::get();
-}
-
 } // namespace folly
 
 #endif // FOLLY_HAZPTR_THR_LOCAL