#error "This should only be included by hazptr.h"
#endif
+/* quality of implementation switches */
+
+// NOTE: The #ifndef pattern is prone to ODR violation. Its use for
+// quality of implementation options is temporary. Eventually these
+// options should be added to the API in future API extensions.
+
+#ifndef HAZPTR_AMB
+#define HAZPTR_AMB true
+#endif
+
+#ifndef HAZPTR_TC
+#define HAZPTR_TC true
+#endif
+
+#ifndef HAZPTR_TC_SIZE
+#define HAZPTR_TC_SIZE 10
+#endif
+
+#ifndef HAZPTR_PRIV
+#define HAZPTR_PRIV true
+#endif
+
+#ifndef HAZPTR_ONE_DOMAIN
+#define HAZPTR_ONE_DOMAIN false
+#endif
+
+#ifndef HAZPTR_SCAN_MULT
+#define HAZPTR_SCAN_MULT 2
+#endif
+
+#ifndef HAZPTR_SCAN_THRESHOLD
+#define HAZPTR_SCAN_THRESHOLD 1000
+#endif
+
+/* stats switch */
+#ifndef HAZPTR_STATS
+#define HAZPTR_STATS false
+#endif
+
+#include <folly/concurrency/CacheLocality.h>
+#include <folly/experimental/AsymmetricMemoryBarrier.h>
#include <folly/experimental/hazptr/debug.h>
-#include <unordered_set>
+#include <mutex> // for thread caching
+#include <unordered_set> // for hash set in bulk reclamation
namespace folly {
namespace hazptr {
-/** hazptr_domain */
+/**
+ * Helper classes and functions
+ */
+
+/** hazptr_stats */
+
+class hazptr_stats;
+
+#if HAZPTR_STATS
+#define INC_HAZPTR_STATS(x) hazptr_stats_.x()
+#else
+#define INC_HAZPTR_STATS(x)
+#endif
-constexpr hazptr_domain::hazptr_domain(memory_resource* mr) noexcept
+/** hazptr_mb */
+
+class hazptr_mb {
+ public:
+ static void light();
+ static void heavy();
+};
+
+/**
+ * TLS structures
+ */
+
+/** TLS life state */
+
+enum hazptr_tls_state { TLS_ALIVE, TLS_UNINITIALIZED, TLS_DESTROYED };
+
+/** hazptr_tc structures
+ * Thread caching of hazptr_rec-s that belong to the default domain.
+ */
+
+struct hazptr_tc_entry {
+ hazptr_rec* hprec_;
+
+ void fill(hazptr_rec* hprec);
+ hazptr_rec* get();
+ void evict();
+};
+
+static_assert(
+ std::is_trivial<hazptr_tc_entry>::value,
+ "hazptr_tc_entry must be trivial"
+ " to avoid a branch to check initialization");
+
+struct hazptr_tc {
+ hazptr_tc_entry entry_[HAZPTR_TC_SIZE];
+ size_t count_;
+#ifndef NDEBUG
+ bool local_;
+#endif
+
+ public:
+ hazptr_tc_entry& operator[](size_t i);
+ hazptr_rec* get();
+ bool put(hazptr_rec* hprec);
+ size_t count();
+};
+
+static_assert(
+ std::is_trivial<hazptr_tc>::value,
+ "hazptr_tc must be trivial to avoid a branch to check initialization");
+
+hazptr_tc* hazptr_tc_tls();
+void hazptr_tc_init();
+void hazptr_tc_shutdown();
+hazptr_rec* hazptr_tc_try_get();
+bool hazptr_tc_try_put(hazptr_rec* hprec);
+
+/** hazptr_priv structures
+ * Thread private lists of retired objects that belong to the default domain.
+ */
+
+struct hazptr_priv {
+ hazptr_obj* head_;
+ hazptr_obj* tail_;
+ int rcount_;
+ bool active_;
+
+ void push(hazptr_obj* obj);
+ void pushAllToDomain();
+};
+
+static_assert(
+ std::is_trivial<hazptr_priv>::value,
+ "hazptr_priv must be trivial to avoid a branch to check initialization");
+
+void hazptr_priv_init();
+void hazptr_priv_shutdown();
+bool hazptr_priv_try_retire(hazptr_obj* obj);
+
+/** hazptr_tls_life */
+
+struct hazptr_tls_life {
+ hazptr_tls_life();
+ ~hazptr_tls_life();
+};
+
+void tls_life_odr_use();
+
+/** tls globals */
+
+extern thread_local hazptr_tls_state tls_state_;
+extern thread_local hazptr_tc tls_tc_data_;
+extern thread_local hazptr_priv tls_priv_data_;
+extern thread_local hazptr_tls_life tls_life_; // last
+
+/**
+ * hazptr_domain
+ */
+
+inline constexpr hazptr_domain::hazptr_domain(memory_resource* mr) noexcept
: mr_(mr) {}
-/** hazptr_obj_base */
+/**
+ * hazptr_obj_base
+ */
template <typename T, typename D>
inline void hazptr_obj_base<T, D>::retire(hazptr_domain& domain, D deleter) {
auto obj = static_cast<T*>(hobp);
hobp->deleter_(obj);
};
+ if (HAZPTR_PRIV &&
+ (HAZPTR_ONE_DOMAIN || (&domain == &default_hazptr_domain()))) {
+ if (hazptr_priv_try_retire(this)) {
+ return;
+ }
+ }
domain.objRetire(this);
}
-/** hazptr_rec */
+/**
+ * hazptr_rec
+ */
class hazptr_rec {
friend class hazptr_domain;
- template <typename> friend class hazptr_owner;
+ friend class hazptr_holder;
+ friend struct hazptr_tc_entry;
- std::atomic<const void*> hazptr_ = {nullptr};
- hazptr_rec* next_ = {nullptr};
- std::atomic<bool> active_ = {false};
+ FOLLY_ALIGN_TO_AVOID_FALSE_SHARING
+ std::atomic<const void*> hazptr_{nullptr};
+ hazptr_rec* next_{nullptr};
+ std::atomic<bool> active_{false};
void set(const void* p) noexcept;
const void* get() const noexcept;
void clear() noexcept;
+ bool isActive() noexcept;
+ bool tryAcquire() noexcept;
void release() noexcept;
};
-/** hazptr_owner */
+/**
+ * hazptr_holder
+ */
-template <typename T>
-inline hazptr_owner<T>::hazptr_owner(hazptr_domain& domain) {
+FOLLY_ALWAYS_INLINE hazptr_holder::hazptr_holder(hazptr_domain& domain) {
domain_ = &domain;
+ if (LIKELY(
+ HAZPTR_TC &&
+ (HAZPTR_ONE_DOMAIN || &domain == &default_hazptr_domain()))) {
+ auto hprec = hazptr_tc_try_get();
+ if (LIKELY(hprec != nullptr)) {
+ hazptr_ = hprec;
+ DEBUG_PRINT(this << " " << domain_ << " " << hazptr_);
+ return;
+ }
+ }
hazptr_ = domain_->hazptrAcquire();
DEBUG_PRINT(this << " " << domain_ << " " << hazptr_);
if (hazptr_ == nullptr) { std::bad_alloc e; throw e; }
}
-template <typename T>
-hazptr_owner<T>::~hazptr_owner() {
+FOLLY_ALWAYS_INLINE hazptr_holder::hazptr_holder(std::nullptr_t) noexcept {
+ domain_ = nullptr;
+ hazptr_ = nullptr;
+ DEBUG_PRINT(this << " " << domain_ << " " << hazptr_);
+}
+
+FOLLY_ALWAYS_INLINE hazptr_holder::~hazptr_holder() {
DEBUG_PRINT(this);
- domain_->hazptrRelease(hazptr_);
+ if (LIKELY(hazptr_ != nullptr)) {
+ hazptr_->clear();
+ if (LIKELY(
+ HAZPTR_TC &&
+ (HAZPTR_ONE_DOMAIN || domain_ == &default_hazptr_domain()))) {
+ if (LIKELY(hazptr_tc_try_put(hazptr_))) {
+ return;
+ }
+ }
+ domain_->hazptrRelease(hazptr_);
+ }
+}
+
+FOLLY_ALWAYS_INLINE hazptr_holder::hazptr_holder(hazptr_holder&& rhs) noexcept {
+ domain_ = rhs.domain_;
+ hazptr_ = rhs.hazptr_;
+ rhs.domain_ = nullptr;
+ rhs.hazptr_ = nullptr;
+}
+
+FOLLY_ALWAYS_INLINE
+hazptr_holder& hazptr_holder::operator=(hazptr_holder&& rhs) noexcept {
+ /* Self-move is a no-op. */
+ if (LIKELY(this != &rhs)) {
+ this->~hazptr_holder();
+ new (this) hazptr_holder(std::move(rhs));
+ }
+ return *this;
}
template <typename T>
-template <typename A>
-inline bool hazptr_owner<T>::try_protect(T*& ptr, const A& src) noexcept {
- static_assert(
- std::is_same<decltype(std::declval<A>().load()), T*>::value,
- "Return type of A::load() must be T*");
+FOLLY_ALWAYS_INLINE bool hazptr_holder::try_protect(
+ T*& ptr,
+ const std::atomic<T*>& src) noexcept {
+ return try_protect(ptr, src, [](T* t) { return t; });
+}
+
+template <typename T, typename Func>
+FOLLY_ALWAYS_INLINE bool hazptr_holder::try_protect(
+ T*& ptr,
+ const std::atomic<T*>& src,
+ Func f) noexcept {
DEBUG_PRINT(this << " " << ptr << " " << &src);
- set(ptr);
- T* p = src.load();
- if (p != ptr) {
+ reset(f(ptr));
+ /*** Full fence ***/ hazptr_mb::light();
+ T* p = src.load(std::memory_order_acquire);
+ if (UNLIKELY(p != ptr)) {
ptr = p;
- clear();
+ reset();
return false;
}
return true;
}
template <typename T>
-template <typename A>
-inline T* hazptr_owner<T>::get_protected(const A& src) noexcept {
- static_assert(
- std::is_same<decltype(std::declval<A>().load()), T*>::value,
- "Return type of A::load() must be T*");
- T* p = src.load();
- while (!try_protect(p, src)) {}
+FOLLY_ALWAYS_INLINE T* hazptr_holder::get_protected(
+ const std::atomic<T*>& src) noexcept {
+ return get_protected(src, [](T* t) { return t; });
+}
+
+template <typename T, typename Func>
+FOLLY_ALWAYS_INLINE T* hazptr_holder::get_protected(
+ const std::atomic<T*>& src,
+ Func f) noexcept {
+ T* p = src.load(std::memory_order_relaxed);
+ while (!try_protect(p, src, f)) {
+ }
DEBUG_PRINT(this << " " << p << " " << &src);
return p;
}
template <typename T>
-inline void hazptr_owner<T>::set(const T* ptr) noexcept {
+FOLLY_ALWAYS_INLINE void hazptr_holder::reset(const T* ptr) noexcept {
auto p = static_cast<hazptr_obj*>(const_cast<T*>(ptr));
DEBUG_PRINT(this << " " << ptr << " p:" << p);
+ DCHECK(hazptr_); // UB if *this is empty
hazptr_->set(p);
}
-template <typename T>
-inline void hazptr_owner<T>::clear() noexcept {
+FOLLY_ALWAYS_INLINE void hazptr_holder::reset(std::nullptr_t) noexcept {
DEBUG_PRINT(this);
+ DCHECK(hazptr_); // UB if *this is empty
hazptr_->clear();
}
-template <typename T>
-inline void hazptr_owner<T>::swap(hazptr_owner<T>& rhs) noexcept {
+FOLLY_ALWAYS_INLINE void hazptr_holder::swap(hazptr_holder& rhs) noexcept {
DEBUG_PRINT(
this << " " << this->hazptr_ << " " << this->domain_ << " -- "
<< &rhs << " " << rhs.hazptr_ << " " << rhs.domain_);
- std::swap(this->domain_, rhs.domain_);
+ if (!HAZPTR_ONE_DOMAIN) {
+ std::swap(this->domain_, rhs.domain_);
+ }
std::swap(this->hazptr_, rhs.hazptr_);
}
-template <typename T>
-inline void swap(hazptr_owner<T>& lhs, hazptr_owner<T>& rhs) noexcept {
+FOLLY_ALWAYS_INLINE void swap(hazptr_holder& lhs, hazptr_holder& rhs) noexcept {
lhs.swap(rhs);
}
-////////////////////////////////////////////////////////////////////////////////
-// Non-template part of implementation
+/**
+ * hazptr_array
+ */
+
+template <size_t M>
+FOLLY_ALWAYS_INLINE hazptr_array<M>::hazptr_array() {
+ auto h = reinterpret_cast<hazptr_holder*>(&raw_);
+ if (HAZPTR_TC) {
+ auto ptc = hazptr_tc_tls();
+ if (LIKELY(ptc != nullptr)) {
+ auto& tc = *ptc;
+ auto count = tc.count();
+ if (M <= count) {
+ size_t offset = count - M;
+ for (size_t i = 0; i < M; ++i) {
+ auto hprec = tc[offset + i].hprec_;
+ DCHECK(hprec != nullptr);
+ DEBUG_PRINT(i << " " << &h[i]);
+ new (&h[i]) hazptr_holder(nullptr);
+ h[i].hazptr_ = hprec;
+ DEBUG_PRINT(
+ i << " " << &h[i] << " " << h[i].domain_ << " " << h[i].hazptr_);
+ }
+ tc.count_ = offset;
+ return;
+ }
+ }
+ }
+ // slow path
+ for (size_t i = 0; i < M; ++i) {
+ new (&h[i]) hazptr_holder;
+ DEBUG_PRINT(
+ i << " " << &h[i] << " " << h[i].domain_ << " " << h[i].hazptr_);
+ }
+}
+
+template <size_t M>
+FOLLY_ALWAYS_INLINE hazptr_array<M>::hazptr_array(
+ hazptr_array&& other) noexcept {
+ DEBUG_PRINT(this << " " << M << " " << &other);
+ auto h = reinterpret_cast<hazptr_holder*>(&raw_);
+ for (size_t i = 0; i < M; ++i) {
+ new (&h[i]) hazptr_holder(std::move(other.h_[i]));
+ DEBUG_PRINT(i << " " << &h[i] << " " << &other.h_[i]);
+ }
+ empty_ = other.empty_;
+ other.empty_ = true;
+}
+
+template <size_t M>
+FOLLY_ALWAYS_INLINE hazptr_array<M>::hazptr_array(std::nullptr_t) noexcept {
+ DEBUG_PRINT(this << " " << M);
+ auto h = reinterpret_cast<hazptr_holder*>(&raw_);
+ for (size_t i = 0; i < M; ++i) {
+ new (&h[i]) hazptr_holder(nullptr);
+ DEBUG_PRINT(i << " " << &h[i]);
+ }
+ empty_ = true;
+}
+
+template <size_t M>
+FOLLY_ALWAYS_INLINE hazptr_array<M>::~hazptr_array() {
+ if (empty_) {
+ return;
+ }
+ auto h = reinterpret_cast<hazptr_holder*>(&raw_);
+ if (HAZPTR_TC) {
+ auto ptc = hazptr_tc_tls();
+ if (LIKELY(ptc != nullptr)) {
+ auto& tc = *ptc;
+ auto count = tc.count();
+ if ((M <= HAZPTR_TC_SIZE) && (count + M <= HAZPTR_TC_SIZE)) {
+ for (size_t i = 0; i < M; ++i) {
+ tc[count + i].hprec_ = h[i].hazptr_;
+ DEBUG_PRINT(i << " " << &h[i]);
+ new (&h[i]) hazptr_holder(nullptr);
+ DEBUG_PRINT(
+ i << " " << &h[i] << " " << h[i].domain_ << " " << h[i].hazptr_);
+ }
+ tc.count_ = count + M;
+ return;
+ }
+ }
+ }
+ // slow path
+ for (size_t i = 0; i < M; ++i) {
+ h[i].~hazptr_holder();
+ }
+}
+
+template <size_t M>
+FOLLY_ALWAYS_INLINE hazptr_array<M>& hazptr_array<M>::operator=(
+ hazptr_array&& other) noexcept {
+ DEBUG_PRINT(this << " " << M << " " << &other);
+ auto h = reinterpret_cast<hazptr_holder*>(&raw_);
+ for (size_t i = 0; i < M; ++i) {
+ h[i] = std::move(other[i]);
+ DEBUG_PRINT(i << " " << &h[i] << " " << &other[i]);
+ }
+ empty_ = other.empty_;
+ other.empty_ = true;
+ return *this;
+}
+
+template <size_t M>
+FOLLY_ALWAYS_INLINE hazptr_holder& hazptr_array<M>::operator[](
+ size_t i) noexcept {
+ auto h = reinterpret_cast<hazptr_holder*>(&raw_);
+ DCHECK(i < M);
+ return h[i];
+}
+
+/**
+ * hazptr_local
+ */
+
+template <size_t M>
+FOLLY_ALWAYS_INLINE hazptr_local<M>::hazptr_local() {
+ auto h = reinterpret_cast<hazptr_holder*>(&raw_);
+ if (HAZPTR_TC) {
+ auto ptc = hazptr_tc_tls();
+ if (LIKELY(ptc != nullptr)) {
+ auto& tc = *ptc;
+ auto count = tc.count();
+ if (M <= count) {
+#ifndef NDEBUG
+ DCHECK(!tc.local_);
+ tc.local_ = true;
+#endif
+ // Fast path
+ for (size_t i = 0; i < M; ++i) {
+ auto hprec = tc[i].hprec_;
+ DCHECK(hprec != nullptr);
+ DEBUG_PRINT(i << " " << &h[i]);
+ new (&h[i]) hazptr_holder(nullptr);
+ h[i].hazptr_ = hprec;
+ DEBUG_PRINT(
+ i << " " << &h[i] << " " << h[i].domain_ << " " << h[i].hazptr_);
+ }
+ return;
+ }
+ }
+ }
+ // Slow path
+ need_destruct_ = true;
+ for (size_t i = 0; i < M; ++i) {
+ new (&h[i]) hazptr_holder;
+ DEBUG_PRINT(
+ i << " " << &h[i] << " " << h[i].domain_ << " " << h[i].hazptr_);
+ }
+}
+
+template <size_t M>
+FOLLY_ALWAYS_INLINE hazptr_local<M>::~hazptr_local() {
+ if (LIKELY(!need_destruct_)) {
+#ifndef NDEBUG
+ auto ptc = hazptr_tc_tls();
+ DCHECK(ptc != nullptr);
+ auto& tc = *ptc;
+ DCHECK(tc.local_);
+ tc.local_ = false;
+#endif
+ return;
+ }
+ // Slow path
+ auto h = reinterpret_cast<hazptr_holder*>(&raw_);
+ for (size_t i = 0; i < M; ++i) {
+ h[i].~hazptr_holder();
+ }
+}
+
+template <size_t M>
+FOLLY_ALWAYS_INLINE hazptr_holder& hazptr_local<M>::operator[](
+ size_t i) noexcept {
+ auto h = reinterpret_cast<hazptr_holder*>(&raw_);
+ DCHECK(i < M);
+ return h[i];
+}
+
////////////////////////////////////////////////////////////////////////////////
// [TODO]:
-// - Thread caching of hazptr_rec-s
-// - Private storage of retired objects
// - Control of reclamation (when and by whom)
-// - Optimized memory order
+// - End-to-end lock-free implementation
/** Definition of default_hazptr_domain() */
-inline hazptr_domain& default_hazptr_domain() {
- static hazptr_domain d;
- DEBUG_PRINT(&d);
- return d;
+
+FOLLY_ALWAYS_INLINE hazptr_domain& default_hazptr_domain() {
+ DEBUG_PRINT(&default_domain_);
+ return default_domain_;
}
/** hazptr_rec */
-inline void hazptr_rec::set(const void* p) noexcept {
+FOLLY_ALWAYS_INLINE void hazptr_rec::set(const void* p) noexcept {
DEBUG_PRINT(this << " " << p);
- hazptr_.store(p);
+ hazptr_.store(p, std::memory_order_release);
}
inline const void* hazptr_rec::get() const noexcept {
- DEBUG_PRINT(this << " " << hazptr_.load());
- return hazptr_.load();
+ auto p = hazptr_.load(std::memory_order_acquire);
+ DEBUG_PRINT(this << " " << p);
+ return p;
}
-inline void hazptr_rec::clear() noexcept {
+FOLLY_ALWAYS_INLINE void hazptr_rec::clear() noexcept {
DEBUG_PRINT(this);
- hazptr_.store(nullptr);
+ hazptr_.store(nullptr, std::memory_order_release);
+}
+
+inline bool hazptr_rec::isActive() noexcept {
+ return active_.load(std::memory_order_acquire);
+}
+
+inline bool hazptr_rec::tryAcquire() noexcept {
+ bool active = isActive();
+ if (!active &&
+ active_.compare_exchange_strong(
+ active, true, std::memory_order_release, std::memory_order_relaxed)) {
+ DEBUG_PRINT(this);
+ return true;
+ }
+ return false;
}
inline void hazptr_rec::release() noexcept {
DEBUG_PRINT(this);
- clear();
- active_.store(false);
+ active_.store(false, std::memory_order_release);
}
/** hazptr_obj */
inline hazptr_domain::~hazptr_domain() {
DEBUG_PRINT(this);
- { /* free all hazptr_rec-s */
- hazptr_rec* next;
- for (auto p = hazptrs_.load(); p; p = next) {
- next = p->next_;
- mr_->deallocate(static_cast<void*>(p), sizeof(hazptr_rec));
- }
- }
{ /* reclaim all remaining retired objects */
hazptr_obj* next;
- for (auto p = retired_.load(); p; p = next) {
+ auto retired = retired_.exchange(nullptr);
+ while (retired) {
+ for (auto p = retired; p; p = next) {
+ next = p->next_;
+ (*(p->reclaim_))(p);
+ }
+ retired = retired_.exchange(nullptr);
+ }
+ }
+ /* Leak the data for the default domain to avoid destruction order
+ * issues with thread caches.
+ */
+ if (this != &default_hazptr_domain()) {
+ /* free all hazptr_rec-s */
+ hazptr_rec* next;
+ for (auto p = hazptrs_.load(std::memory_order_acquire); p; p = next) {
next = p->next_;
- (*(p->reclaim_))(p);
+ DCHECK(!p->isActive());
+ mr_->deallocate(static_cast<void*>(p), sizeof(hazptr_rec));
}
}
}
-inline void hazptr_domain::try_reclaim() {
- DEBUG_PRINT(this);
- rcount_.exchange(0);
- bulkReclaim();
-}
-
inline hazptr_rec* hazptr_domain::hazptrAcquire() {
hazptr_rec* p;
hazptr_rec* next;
- for (p = hazptrs_.load(); p; p = next) {
+ for (p = hazptrs_.load(std::memory_order_acquire); p; p = next) {
next = p->next_;
- bool active = p->active_.load();
- if (!active) {
- if (p->active_.compare_exchange_weak(active, true)) {
- DEBUG_PRINT(this << " " << p);
- return p;
- }
+ if (p->tryAcquire()) {
+ return p;
}
}
p = static_cast<hazptr_rec*>(mr_->allocate(sizeof(hazptr_rec)));
+ DEBUG_PRINT(this << " " << p << " " << sizeof(hazptr_rec));
if (p == nullptr) {
return nullptr;
}
- p->active_.store(true);
- do {
- p->next_ = hazptrs_.load();
- if (hazptrs_.compare_exchange_weak(p->next_, p)) {
- break;
- }
- } while (true);
+ p->active_.store(true, std::memory_order_relaxed);
+ p->next_ = hazptrs_.load(std::memory_order_acquire);
+ while (!hazptrs_.compare_exchange_weak(
+ p->next_, p, std::memory_order_release, std::memory_order_acquire))
+ /* keep trying */;
auto hcount = hcount_.fetch_add(1);
DEBUG_PRINT(this << " " << p << " " << sizeof(hazptr_rec) << " " << hcount);
return p;
inline int
hazptr_domain::pushRetired(hazptr_obj* head, hazptr_obj* tail, int count) {
- tail->next_ = retired_.load();
- while (!retired_.compare_exchange_weak(tail->next_, head)) {}
- return rcount_.fetch_add(count);
+ /*** Full fence ***/ hazptr_mb::light();
+ tail->next_ = retired_.load(std::memory_order_acquire);
+ while (!retired_.compare_exchange_weak(
+ tail->next_,
+ head,
+ std::memory_order_release,
+ std::memory_order_acquire)) {
+ }
+ return rcount_.fetch_add(count) + count;
+}
+
+inline bool hazptr_domain::reachedThreshold(int rcount) {
+ return (
+ rcount >= HAZPTR_SCAN_THRESHOLD &&
+ rcount >= HAZPTR_SCAN_MULT * hcount_.load(std::memory_order_acquire));
}
inline void hazptr_domain::objRetire(hazptr_obj* p) {
- auto rcount = pushRetired(p, p, 1) + 1;
- if (rcount >= kScanThreshold * hcount_.load()) {
+ auto rcount = pushRetired(p, p, 1);
+ if (reachedThreshold(rcount)) {
tryBulkReclaim();
}
}
inline void hazptr_domain::tryBulkReclaim() {
DEBUG_PRINT(this);
do {
- auto hcount = hcount_.load();
- auto rcount = rcount_.load();
- if (rcount < kScanThreshold * hcount) {
+ auto hcount = hcount_.load(std::memory_order_acquire);
+ auto rcount = rcount_.load(std::memory_order_acquire);
+ if (rcount < HAZPTR_SCAN_THRESHOLD || rcount < HAZPTR_SCAN_MULT * hcount) {
return;
}
- if (rcount_.compare_exchange_weak(rcount, 0)) {
+ if (rcount_.compare_exchange_weak(
+ rcount, 0, std::memory_order_release, std::memory_order_relaxed)) {
break;
}
} while (true);
inline void hazptr_domain::bulkReclaim() {
DEBUG_PRINT(this);
- auto p = retired_.exchange(nullptr);
- auto h = hazptrs_.load();
- std::unordered_set<const void*> hs;
+ /*** Full fence ***/ hazptr_mb::heavy();
+ auto p = retired_.exchange(nullptr, std::memory_order_acquire);
+ auto h = hazptrs_.load(std::memory_order_acquire);
+ std::unordered_set<const void*> hs; // TODO lock-free alternative
for (; h; h = h->next_) {
- hs.insert(h->hazptr_.load());
+ hs.insert(h->get());
}
int rcount = 0;
hazptr_obj* retired = nullptr;
}
}
+/** hazptr_stats */
+
+class hazptr_stats {
+ public:
+ ~hazptr_stats();
+ void light();
+ void heavy();
+ void seq_cst();
+
+ private:
+ std::atomic<uint64_t> light_{0};
+ std::atomic<uint64_t> heavy_{0};
+ std::atomic<uint64_t> seq_cst_{0};
+};
+
+extern hazptr_stats hazptr_stats_;
+
+inline hazptr_stats::~hazptr_stats() {
+ DEBUG_PRINT(this << " light " << light_.load());
+ DEBUG_PRINT(this << " heavy " << heavy_.load());
+ DEBUG_PRINT(this << " seq_cst " << seq_cst_.load());
+}
+
+FOLLY_ALWAYS_INLINE void hazptr_stats::light() {
+ if (HAZPTR_STATS) {
+ /* atomic */ ++light_;
+ }
+}
+
+inline void hazptr_stats::heavy() {
+ if (HAZPTR_STATS) {
+ /* atomic */ ++heavy_;
+ }
+}
+
+inline void hazptr_stats::seq_cst() {
+ if (HAZPTR_STATS) {
+ /* atomic */ ++seq_cst_;
+ }
+}
+
+/** hazptr_mb */
+
+FOLLY_ALWAYS_INLINE void hazptr_mb::light() {
+ DEBUG_PRINT("");
+ if (HAZPTR_AMB) {
+ folly::asymmetricLightBarrier();
+ INC_HAZPTR_STATS(light);
+ } else {
+ atomic_thread_fence(std::memory_order_seq_cst);
+ INC_HAZPTR_STATS(seq_cst);
+ }
+}
+
+inline void hazptr_mb::heavy() {
+ DEBUG_PRINT("");
+ if (HAZPTR_AMB) {
+ folly::asymmetricHeavyBarrier(AMBFlags::EXPEDITED);
+ INC_HAZPTR_STATS(heavy);
+ } else {
+ atomic_thread_fence(std::memory_order_seq_cst);
+ INC_HAZPTR_STATS(seq_cst);
+ }
+}
+
+/**
+ * TLS structures
+ */
+
+/**
+ * hazptr_tc structures
+ */
+
+/** hazptr_tc_entry */
+
+FOLLY_ALWAYS_INLINE void hazptr_tc_entry::fill(hazptr_rec* hprec) {
+ hprec_ = hprec;
+ DEBUG_PRINT(this << " " << hprec);
+}
+
+FOLLY_ALWAYS_INLINE hazptr_rec* hazptr_tc_entry::get() {
+ auto hprec = hprec_;
+ DEBUG_PRINT(this << " " << hprec);
+ return hprec;
+}
+
+inline void hazptr_tc_entry::evict() {
+ auto hprec = hprec_;
+ hprec->release();
+ DEBUG_PRINT(this << " " << hprec);
+}
+
+/** hazptr_tc */
+
+FOLLY_ALWAYS_INLINE hazptr_tc_entry& hazptr_tc::operator[](size_t i) {
+ DCHECK(i <= HAZPTR_TC_SIZE);
+ return entry_[i];
+}
+
+FOLLY_ALWAYS_INLINE hazptr_rec* hazptr_tc::get() {
+ if (LIKELY(count_ != 0)) {
+ auto hprec = entry_[--count_].get();
+ DEBUG_PRINT(this << " " << hprec);
+ return hprec;
+ }
+ DEBUG_PRINT(this << " nullptr");
+ return nullptr;
+}
+
+FOLLY_ALWAYS_INLINE bool hazptr_tc::put(hazptr_rec* hprec) {
+ if (LIKELY(count_ < HAZPTR_TC_SIZE)) {
+ entry_[count_++].fill(hprec);
+ DEBUG_PRINT(this << " " << count_ - 1);
+ return true;
+ }
+ return false;
+}
+
+FOLLY_ALWAYS_INLINE size_t hazptr_tc::count() {
+ return count_;
+}
+
+/** hazptr_tc free functions */
+
+FOLLY_ALWAYS_INLINE hazptr_tc* hazptr_tc_tls() {
+ DEBUG_PRINT(tls_state_);
+ if (LIKELY(tls_state_ == TLS_ALIVE)) {
+ DEBUG_PRINT(tls_state_);
+ return &tls_tc_data_;
+ } else if (tls_state_ == TLS_UNINITIALIZED) {
+ tls_life_odr_use();
+ return &tls_tc_data_;
+ }
+ return nullptr;
+}
+
+inline void hazptr_tc_init() {
+ DEBUG_PRINT("");
+ auto& tc = tls_tc_data_;
+ DEBUG_PRINT(&tc);
+ tc.count_ = 0;
+#ifndef NDEBUG
+ tc.local_ = false;
+#endif
+}
+
+inline void hazptr_tc_shutdown() {
+ auto& tc = tls_tc_data_;
+ DEBUG_PRINT(&tc);
+ for (size_t i = 0; i < tc.count_; ++i) {
+ tc.entry_[i].evict();
+ }
+}
+
+FOLLY_ALWAYS_INLINE hazptr_rec* hazptr_tc_try_get() {
+ DEBUG_PRINT(TLS_UNINITIALIZED << TLS_ALIVE << TLS_DESTROYED);
+ DEBUG_PRINT(tls_state_);
+ if (LIKELY(tls_state_ == TLS_ALIVE)) {
+ DEBUG_PRINT(tls_state_);
+ return tls_tc_data_.get();
+ } else if (tls_state_ == TLS_UNINITIALIZED) {
+ tls_life_odr_use();
+ return tls_tc_data_.get();
+ }
+ return nullptr;
+}
+
+FOLLY_ALWAYS_INLINE bool hazptr_tc_try_put(hazptr_rec* hprec) {
+ DEBUG_PRINT(tls_state_);
+ if (LIKELY(tls_state_ == TLS_ALIVE)) {
+ DEBUG_PRINT(tls_state_);
+ return tls_tc_data_.put(hprec);
+ }
+ return false;
+}
+
+/**
+ * hazptr_priv
+ */
+
+inline void hazptr_priv::push(hazptr_obj* obj) {
+ auto& domain = default_hazptr_domain();
+ obj->next_ = nullptr;
+ if (tail_) {
+ tail_->next_ = obj;
+ } else {
+ if (!active_) {
+ domain.objRetire(obj);
+ return;
+ }
+ head_ = obj;
+ }
+ tail_ = obj;
+ ++rcount_;
+ if (domain.reachedThreshold(rcount_)) {
+ pushAllToDomain();
+ }
+}
+
+inline void hazptr_priv::pushAllToDomain() {
+ auto& domain = default_hazptr_domain();
+ domain.pushRetired(head_, tail_, rcount_);
+ head_ = nullptr;
+ tail_ = nullptr;
+ rcount_ = 0;
+ domain.tryBulkReclaim();
+}
+
+inline void hazptr_priv_init() {
+ auto& priv = tls_priv_data_;
+ DEBUG_PRINT(&priv);
+ priv.head_ = nullptr;
+ priv.tail_ = nullptr;
+ priv.rcount_ = 0;
+ priv.active_ = true;
+}
+
+inline void hazptr_priv_shutdown() {
+ auto& priv = tls_priv_data_;
+ DEBUG_PRINT(&priv);
+ DCHECK(priv.active_);
+ priv.active_ = false;
+ if (priv.tail_) {
+ priv.pushAllToDomain();
+ }
+}
+
+inline bool hazptr_priv_try_retire(hazptr_obj* obj) {
+ DEBUG_PRINT(tls_state_);
+ if (tls_state_ == TLS_ALIVE) {
+ DEBUG_PRINT(tls_state_);
+ tls_priv_data_.push(obj);
+ return true;
+ } else if (tls_state_ == TLS_UNINITIALIZED) {
+ DEBUG_PRINT(tls_state_);
+ tls_life_odr_use();
+ tls_priv_data_.push(obj);
+ return true;
+ }
+ return false;
+}
+
+/** hazptr_tls_life */
+
+inline void tls_life_odr_use() {
+ DEBUG_PRINT(tls_state_);
+ CHECK(tls_state_ == TLS_UNINITIALIZED);
+ auto volatile tlsOdrUse = &tls_life_;
+ CHECK(tlsOdrUse != nullptr);
+ DEBUG_PRINT(tlsOdrUse);
+}
+
+inline hazptr_tls_life::hazptr_tls_life() {
+ DEBUG_PRINT(this);
+ CHECK(tls_state_ == TLS_UNINITIALIZED);
+ hazptr_tc_init();
+ hazptr_priv_init();
+ tls_state_ = TLS_ALIVE;
+}
+
+inline hazptr_tls_life::~hazptr_tls_life() {
+ DEBUG_PRINT(this);
+ CHECK(tls_state_ == TLS_ALIVE);
+ hazptr_tc_shutdown();
+ hazptr_priv_shutdown();
+ tls_state_ = TLS_DESTROYED;
+}
+
} // namespace folly
} // namespace hazptr