* limitations under the License.
*/
-/*
- * N.B. You most likely do _not_ want to use RWSpinLock or any other
- * kind of spinlock. Use SharedMutex instead.
- *
- * In short, spinlocks in preemptive multi-tasking operating systems
- * have serious problems and fast mutexes like SharedMutex are almost
- * certainly the better choice, because letting the OS scheduler put a
- * thread to sleep is better for system responsiveness and throughput
- * than wasting a timeslice repeatedly querying a lock held by a
- * thread that's blocked, and you can't prevent userspace
- * programs blocking.
- *
- * Spinlocks in an operating system kernel make much more sense than
- * they do in userspace.
- *
- * -------------------------------------------------------------------
- *
- * Two Read-Write spin lock implementations.
- *
- * Ref: http://locklessinc.com/articles/locks
- *
- * Both locks here are faster than pthread_rwlock and have very low
- * overhead (usually 20-30ns). They don't use any system mutexes and
- * are very compact (4/8 bytes), so are suitable for per-instance
- * based locking, particularly when contention is not expected.
- *
- * For a spinlock, RWSpinLock is a reasonable choice. (See the note
- * about for why a spin lock is frequently a bad idea generally.)
- * RWSpinLock has minimal overhead, and comparable contention
- * performance when the number of competing threads is less than or
- * equal to the number of logical CPUs. Even as the number of
- * threads gets larger, RWSpinLock can still be very competitive in
- * READ, although it is slower on WRITE, and also inherently unfair
- * to writers.
- *
- * RWTicketSpinLock shows more balanced READ/WRITE performance. If
- * your application really needs a lot more threads, and a
- * higher-priority writer, prefer one of the RWTicketSpinLock locks.
- *
- * Caveats:
- *
- * RWTicketSpinLock locks can only be used with GCC on x86/x86-64
- * based systems.
- *
- * RWTicketSpinLock<32> only allows up to 2^8 - 1 concurrent
- * readers and writers.
- *
- * RWTicketSpinLock<64> only allows up to 2^16 - 1 concurrent
- * readers and writers.
- *
- * RWTicketSpinLock<..., true> (kFavorWriter = true, that is, strict
- * writer priority) is NOT reentrant, even for lock_shared().
- *
- * The lock will not grant any new shared (read) accesses while a thread
- * attempting to acquire the lock in write mode is blocked. (That is,
- * if the lock is held in shared mode by N threads, and a thread attempts
- * to acquire it in write mode, no one else can acquire it in shared mode
- * until these N threads release the lock and then the blocked thread
- * acquires and releases the exclusive lock.) This also applies for
- * attempts to reacquire the lock in shared mode by threads that already
- * hold it in shared mode, making the lock non-reentrant.
- *
- * RWSpinLock handles 2^30 - 1 concurrent readers.
- *
- * @author Xin Liu <xliux@fb.com>
- */
-
-#pragma once
-
-/*
-========================================================================
-Benchmark on (Intel(R) Xeon(R) CPU L5630 @ 2.13GHz) 8 cores(16 HTs)
-========================================================================
-
-------------------------------------------------------------------------------
-1. Single thread benchmark (read/write lock + unlock overhead)
-Benchmark Iters Total t t/iter iter/sec
--------------------------------------------------------------------------------
-* BM_RWSpinLockRead 100000 1.786 ms 17.86 ns 53.4M
-+30.5% BM_RWSpinLockWrite 100000 2.331 ms 23.31 ns 40.91M
-+85.7% BM_RWTicketSpinLock32Read 100000 3.317 ms 33.17 ns 28.75M
-+96.0% BM_RWTicketSpinLock32Write 100000 3.5 ms 35 ns 27.25M
-+85.6% BM_RWTicketSpinLock64Read 100000 3.315 ms 33.15 ns 28.77M
-+96.0% BM_RWTicketSpinLock64Write 100000 3.5 ms 35 ns 27.25M
-+85.7% BM_RWTicketSpinLock32FavorWriterRead 100000 3.317 ms 33.17 ns 28.75M
-+29.7% BM_RWTicketSpinLock32FavorWriterWrite 100000 2.316 ms 23.16 ns 41.18M
-+85.3% BM_RWTicketSpinLock64FavorWriterRead 100000 3.309 ms 33.09 ns 28.82M
-+30.2% BM_RWTicketSpinLock64FavorWriterWrite 100000 2.325 ms 23.25 ns 41.02M
-+ 175% BM_PThreadRWMutexRead 100000 4.917 ms 49.17 ns 19.4M
-+ 166% BM_PThreadRWMutexWrite 100000 4.757 ms 47.57 ns 20.05M
-
-------------------------------------------------------------------------------
-2. Contention Benchmark 90% read 10% write
-Benchmark hits average min max sigma
-------------------------------------------------------------------------------
----------- 8 threads ------------
-RWSpinLock Write 142666 220ns 78ns 40.8us 269ns
-RWSpinLock Read 1282297 222ns 80ns 37.7us 248ns
-RWTicketSpinLock Write 85692 209ns 71ns 17.9us 252ns
-RWTicketSpinLock Read 769571 215ns 78ns 33.4us 251ns
-pthread_rwlock_t Write 84248 2.48us 99ns 269us 8.19us
-pthread_rwlock_t Read 761646 933ns 101ns 374us 3.25us
-
----------- 16 threads ------------
-RWSpinLock Write 124236 237ns 78ns 261us 801ns
-RWSpinLock Read 1115807 236ns 78ns 2.27ms 2.17us
-RWTicketSpinLock Write 81781 231ns 71ns 31.4us 351ns
-RWTicketSpinLock Read 734518 238ns 78ns 73.6us 379ns
-pthread_rwlock_t Write 83363 7.12us 99ns 785us 28.1us
-pthread_rwlock_t Read 754978 2.18us 101ns 1.02ms 14.3us
-
----------- 50 threads ------------
-RWSpinLock Write 131142 1.37us 82ns 7.53ms 68.2us
-RWSpinLock Read 1181240 262ns 78ns 6.62ms 12.7us
-RWTicketSpinLock Write 83045 397ns 73ns 7.01ms 31.5us
-RWTicketSpinLock Read 744133 386ns 78ns 11ms 31.4us
-pthread_rwlock_t Write 80849 112us 103ns 4.52ms 263us
-pthread_rwlock_t Read 728698 24us 101ns 7.28ms 194us
-
-*/
-
-#include <folly/Portability.h>
-#include <folly/portability/Asm.h>
-
-#if defined(__GNUC__) && (defined(__i386) || FOLLY_X64 || defined(ARCH_K8))
-#define RW_SPINLOCK_USE_X86_INTRINSIC_
-#include <x86intrin.h>
-#elif defined(_MSC_VER) && defined(FOLLY_X64)
-#define RW_SPINLOCK_USE_X86_INTRINSIC_
-#elif FOLLY_AARCH64
-#define RW_SPINLOCK_USE_X86_INTRINSIC_
-#else
-#undef RW_SPINLOCK_USE_X86_INTRINSIC_
-#endif
-
-// iOS doesn't define _mm_cvtsi64_si128 and friends
-#if (FOLLY_SSE >= 2) && !FOLLY_MOBILE && FOLLY_X64
-#define RW_SPINLOCK_USE_SSE_INSTRUCTIONS_
-#else
-#undef RW_SPINLOCK_USE_SSE_INSTRUCTIONS_
-#endif
-
-#include <algorithm>
-#include <atomic>
-#include <string>
-#include <thread>
-
-#include <glog/logging.h>
-
-#include <folly/Likely.h>
-
-namespace folly {
-
-/*
- * A simple, small (4-bytes), but unfair rwlock. Use it when you want
- * a nice writer and don't expect a lot of write/read contention, or
- * when you need small rwlocks since you are creating a large number
- * of them.
- *
- * Note that the unfairness here is extreme: if the lock is
- * continually accessed for read, writers will never get a chance. If
- * the lock can be that highly contended this class is probably not an
- * ideal choice anyway.
- *
- * It currently implements most of the Lockable, SharedLockable and
- * UpgradeLockable concepts except the TimedLockable related locking/unlocking
- * interfaces.
- */
-class RWSpinLock {
- enum : int32_t { READER = 4, UPGRADED = 2, WRITER = 1 };
- public:
- constexpr RWSpinLock() : bits_(0) {}
-
- RWSpinLock(RWSpinLock const&) = delete;
- RWSpinLock& operator=(RWSpinLock const&) = delete;
-
- // Lockable Concept
- void lock() {
- uint_fast32_t count = 0;
- while (!LIKELY(try_lock())) {
- if (++count > 1000) {
- std::this_thread::yield();
- }
- }
- }
-
- // Writer is responsible for clearing up both the UPGRADED and WRITER bits.
- void unlock() {
- static_assert(READER > WRITER + UPGRADED, "wrong bits!");
- bits_.fetch_and(~(WRITER | UPGRADED), std::memory_order_release);
- }
-
- // SharedLockable Concept
- void lock_shared() {
- uint_fast32_t count = 0;
- while (!LIKELY(try_lock_shared())) {
- if (++count > 1000) {
- std::this_thread::yield();
- }
- }
- }
-
- void unlock_shared() {
- bits_.fetch_add(-READER, std::memory_order_release);
- }
-
- // Downgrade the lock from writer status to reader status.
- void unlock_and_lock_shared() {
- bits_.fetch_add(READER, std::memory_order_acquire);
- unlock();
- }
-
- // UpgradeLockable Concept
- void lock_upgrade() {
- uint_fast32_t count = 0;
- while (!try_lock_upgrade()) {
- if (++count > 1000) {
- std::this_thread::yield();
- }
- }
- }
-
- void unlock_upgrade() {
- bits_.fetch_add(-UPGRADED, std::memory_order_acq_rel);
- }
-
- // unlock upgrade and try to acquire write lock
- void unlock_upgrade_and_lock() {
- int64_t count = 0;
- while (!try_unlock_upgrade_and_lock()) {
- if (++count > 1000) {
- std::this_thread::yield();
- }
- }
- }
-
- // unlock upgrade and read lock atomically
- void unlock_upgrade_and_lock_shared() {
- bits_.fetch_add(READER - UPGRADED, std::memory_order_acq_rel);
- }
-
- // write unlock and upgrade lock atomically
- void unlock_and_lock_upgrade() {
- // need to do it in two steps here -- as the UPGRADED bit might be OR-ed at
- // the same time when other threads are trying do try_lock_upgrade().
- bits_.fetch_or(UPGRADED, std::memory_order_acquire);
- bits_.fetch_add(-WRITER, std::memory_order_release);
- }
-
-
- // Attempt to acquire writer permission. Return false if we didn't get it.
- bool try_lock() {
- int32_t expect = 0;
- return bits_.compare_exchange_strong(expect, WRITER,
- std::memory_order_acq_rel);
- }
-
- // Try to get reader permission on the lock. This can fail if we
- // find out someone is a writer or upgrader.
- // Setting the UPGRADED bit would allow a writer-to-be to indicate
- // its intention to write and block any new readers while waiting
- // for existing readers to finish and release their read locks. This
- // helps avoid starving writers (promoted from upgraders).
- bool try_lock_shared() {
- // fetch_add is considerably (100%) faster than compare_exchange,
- // so here we are optimizing for the common (lock success) case.
- int32_t value = bits_.fetch_add(READER, std::memory_order_acquire);
- if (UNLIKELY(value & (WRITER|UPGRADED))) {
- bits_.fetch_add(-READER, std::memory_order_release);
- return false;
- }
- return true;
- }
-
- // try to unlock upgrade and write lock atomically
- bool try_unlock_upgrade_and_lock() {
- int32_t expect = UPGRADED;
- return bits_.compare_exchange_strong(expect, WRITER,
- std::memory_order_acq_rel);
- }
-
- // try to acquire an upgradable lock.
- bool try_lock_upgrade() {
- int32_t value = bits_.fetch_or(UPGRADED, std::memory_order_acquire);
-
- // Note: when failed, we cannot flip the UPGRADED bit back,
- // as in this case there is either another upgrade lock or a write lock.
- // If it's a write lock, the bit will get cleared up when that lock's done
- // with unlock().
- return ((value & (UPGRADED | WRITER)) == 0);
- }
-
- // mainly for debugging purposes.
- int32_t bits() const { return bits_.load(std::memory_order_acquire); }
-
- class ReadHolder;
- class UpgradedHolder;
- class WriteHolder;
-
- class ReadHolder {
- public:
- explicit ReadHolder(RWSpinLock* lock) : lock_(lock) {
- if (lock_) {
- lock_->lock_shared();
- }
- }
-
- explicit ReadHolder(RWSpinLock& lock) : lock_(&lock) {
- lock_->lock_shared();
- }
-
- ReadHolder(ReadHolder&& other) noexcept : lock_(other.lock_) {
- other.lock_ = nullptr;
- }
-
- // down-grade
- explicit ReadHolder(UpgradedHolder&& upgraded) : lock_(upgraded.lock_) {
- upgraded.lock_ = nullptr;
- if (lock_) {
- lock_->unlock_upgrade_and_lock_shared();
- }
- }
-
- explicit ReadHolder(WriteHolder&& writer) : lock_(writer.lock_) {
- writer.lock_ = nullptr;
- if (lock_) {
- lock_->unlock_and_lock_shared();
- }
- }
-
- ReadHolder& operator=(ReadHolder&& other) {
- using std::swap;
- swap(lock_, other.lock_);
- return *this;
- }
-
- ReadHolder(const ReadHolder& other) = delete;
- ReadHolder& operator=(const ReadHolder& other) = delete;
-
- ~ReadHolder() {
- if (lock_) {
- lock_->unlock_shared();
- }
- }
-
- void reset(RWSpinLock* lock = nullptr) {
- if (lock == lock_) {
- return;
- }
- if (lock_) {
- lock_->unlock_shared();
- }
- lock_ = lock;
- if (lock_) {
- lock_->lock_shared();
- }
- }
-
- void swap(ReadHolder* other) {
- std::swap(lock_, other->lock_);
- }
-
- private:
- friend class UpgradedHolder;
- friend class WriteHolder;
- RWSpinLock* lock_;
- };
-
- class UpgradedHolder {
- public:
- explicit UpgradedHolder(RWSpinLock* lock) : lock_(lock) {
- if (lock_) {
- lock_->lock_upgrade();
- }
- }
-
- explicit UpgradedHolder(RWSpinLock& lock) : lock_(&lock) {
- lock_->lock_upgrade();
- }
-
- explicit UpgradedHolder(WriteHolder&& writer) {
- lock_ = writer.lock_;
- writer.lock_ = nullptr;
- if (lock_) {
- lock_->unlock_and_lock_upgrade();
- }
- }
-
- UpgradedHolder(UpgradedHolder&& other) noexcept : lock_(other.lock_) {
- other.lock_ = nullptr;
- }
-
- UpgradedHolder& operator =(UpgradedHolder&& other) {
- using std::swap;
- swap(lock_, other.lock_);
- return *this;
- }
-
- UpgradedHolder(const UpgradedHolder& other) = delete;
- UpgradedHolder& operator =(const UpgradedHolder& other) = delete;
-
- ~UpgradedHolder() {
- if (lock_) {
- lock_->unlock_upgrade();
- }
- }
-
- void reset(RWSpinLock* lock = nullptr) {
- if (lock == lock_) {
- return;
- }
- if (lock_) {
- lock_->unlock_upgrade();
- }
- lock_ = lock;
- if (lock_) {
- lock_->lock_upgrade();
- }
- }
-
- void swap(UpgradedHolder* other) {
- using std::swap;
- swap(lock_, other->lock_);
- }
-
- private:
- friend class WriteHolder;
- friend class ReadHolder;
- RWSpinLock* lock_;
- };
-
- class WriteHolder {
- public:
- explicit WriteHolder(RWSpinLock* lock) : lock_(lock) {
- if (lock_) {
- lock_->lock();
- }
- }
-
- explicit WriteHolder(RWSpinLock& lock) : lock_(&lock) {
- lock_->lock();
- }
-
- // promoted from an upgrade lock holder
- explicit WriteHolder(UpgradedHolder&& upgraded) {
- lock_ = upgraded.lock_;
- upgraded.lock_ = nullptr;
- if (lock_) {
- lock_->unlock_upgrade_and_lock();
- }
- }
-
- WriteHolder(WriteHolder&& other) noexcept : lock_(other.lock_) {
- other.lock_ = nullptr;
- }
-
- WriteHolder& operator =(WriteHolder&& other) {
- using std::swap;
- swap(lock_, other.lock_);
- return *this;
- }
-
- WriteHolder(const WriteHolder& other) = delete;
- WriteHolder& operator =(const WriteHolder& other) = delete;
-
- ~WriteHolder() {
- if (lock_) {
- lock_->unlock();
- }
- }
-
- void reset(RWSpinLock* lock = nullptr) {
- if (lock == lock_) {
- return;
- }
- if (lock_) {
- lock_->unlock();
- }
- lock_ = lock;
- if (lock_) {
- lock_->lock();
- }
- }
-
- void swap(WriteHolder* other) {
- using std::swap;
- swap(lock_, other->lock_);
- }
-
- private:
- friend class ReadHolder;
- friend class UpgradedHolder;
- RWSpinLock* lock_;
- };
-
- private:
- std::atomic<int32_t> bits_;
-};
-
-
-#ifdef RW_SPINLOCK_USE_X86_INTRINSIC_
-// A more balanced Read-Write spin lock implemented based on GCC intrinsics.
-
-namespace detail {
-template <size_t kBitWidth> struct RWTicketIntTrait {
- static_assert(kBitWidth == 32 || kBitWidth == 64,
- "bit width has to be either 32 or 64 ");
-};
-
-template <>
-struct RWTicketIntTrait<64> {
- typedef uint64_t FullInt;
- typedef uint32_t HalfInt;
- typedef uint16_t QuarterInt;
-
-#ifdef RW_SPINLOCK_USE_SSE_INSTRUCTIONS_
- static __m128i make128(const uint16_t v[4]) {
- return _mm_set_epi16(0, 0, 0, 0,
- short(v[3]), short(v[2]), short(v[1]), short(v[0]));
- }
- static inline __m128i fromInteger(uint64_t from) {
- return _mm_cvtsi64_si128(int64_t(from));
- }
- static inline uint64_t toInteger(__m128i in) {
- return uint64_t(_mm_cvtsi128_si64(in));
- }
- static inline uint64_t addParallel(__m128i in, __m128i kDelta) {
- return toInteger(_mm_add_epi16(in, kDelta));
- }
-#endif
-};
-
-template <>
-struct RWTicketIntTrait<32> {
- typedef uint32_t FullInt;
- typedef uint16_t HalfInt;
- typedef uint8_t QuarterInt;
-
-#ifdef RW_SPINLOCK_USE_SSE_INSTRUCTIONS_
- static __m128i make128(const uint8_t v[4]) {
- return _mm_set_epi8(
- 0, 0, 0, 0,
- 0, 0, 0, 0,
- 0, 0, 0, 0,
- char(v[3]), char(v[2]), char(v[1]), char(v[0]));
- }
- static inline __m128i fromInteger(uint32_t from) {
- return _mm_cvtsi32_si128(int32_t(from));
- }
- static inline uint32_t toInteger(__m128i in) {
- return uint32_t(_mm_cvtsi128_si32(in));
- }
- static inline uint32_t addParallel(__m128i in, __m128i kDelta) {
- return toInteger(_mm_add_epi8(in, kDelta));
- }
-#endif
-};
-} // namespace detail
-
-template <size_t kBitWidth, bool kFavorWriter = false>
-class RWTicketSpinLockT {
- typedef detail::RWTicketIntTrait<kBitWidth> IntTraitType;
- typedef typename detail::RWTicketIntTrait<kBitWidth>::FullInt FullInt;
- typedef typename detail::RWTicketIntTrait<kBitWidth>::HalfInt HalfInt;
- typedef typename detail::RWTicketIntTrait<kBitWidth>::QuarterInt
- QuarterInt;
-
- union RWTicket {
- constexpr RWTicket() : whole(0) {}
- FullInt whole;
- HalfInt readWrite;
- __extension__ struct {
- QuarterInt write;
- QuarterInt read;
- QuarterInt users;
- };
- } ticket;
-
- private: // Some x64-specific utilities for atomic access to ticket.
- template <class T> static T load_acquire(T* addr) {
- T t = *addr; // acquire barrier
- asm_volatile_memory();
- return t;
- }
-
- template <class T>
- static void store_release(T* addr, T v) {
- asm_volatile_memory();
- *addr = v; // release barrier
- }
-
- public:
-
- constexpr RWTicketSpinLockT() {}
-
- RWTicketSpinLockT(RWTicketSpinLockT const&) = delete;
- RWTicketSpinLockT& operator=(RWTicketSpinLockT const&) = delete;
-
- void lock() {
- if (kFavorWriter) {
- writeLockAggressive();
- } else {
- writeLockNice();
- }
- }
-
- /*
- * Both try_lock and try_lock_shared diverge in our implementation from the
- * lock algorithm described in the link above.
- *
- * In the read case, it is undesirable that the readers could wait
- * for another reader (before increasing ticket.read in the other
- * implementation). Our approach gives up on
- * first-come-first-serve, but our benchmarks showed improve
- * performance for both readers and writers under heavily contended
- * cases, particularly when the number of threads exceeds the number
- * of logical CPUs.
- *
- * We have writeLockAggressive() using the original implementation
- * for a writer, which gives some advantage to the writer over the
- * readers---for that path it is guaranteed that the writer will
- * acquire the lock after all the existing readers exit.
- */
- bool try_lock() {
- RWTicket t;
- FullInt old = t.whole = load_acquire(&ticket.whole);
- if (t.users != t.write) {
- return false;
- }
- ++t.users;
- return __sync_bool_compare_and_swap(&ticket.whole, old, t.whole);
- }
-
- /*
- * Call this if you want to prioritize writer to avoid starvation.
- * Unlike writeLockNice, immediately acquires the write lock when
- * the existing readers (arriving before the writer) finish their
- * turns.
- */
- void writeLockAggressive() {
- // std::this_thread::yield() is needed here to avoid a pathology if the number
- // of threads attempting concurrent writes is >= the number of real
- // cores allocated to this process. This is less likely than the
- // corresponding situation in lock_shared(), but we still want to
- // avoid it
- uint_fast32_t count = 0;
- QuarterInt val = __sync_fetch_and_add(&ticket.users, 1);
- while (val != load_acquire(&ticket.write)) {
- asm_volatile_pause();
- if (UNLIKELY(++count > 1000)) {
- std::this_thread::yield();
- }
- }
- }
-
- // Call this when the writer should be nicer to the readers.
- void writeLockNice() {
- // Here it doesn't cpu-relax the writer.
- //
- // This is because usually we have many more readers than the
- // writers, so the writer has less chance to get the lock when
- // there are a lot of competing readers. The aggressive spinning
- // can help to avoid starving writers.
- //
- // We don't worry about std::this_thread::yield() here because the caller
- // has already explicitly abandoned fairness.
- while (!try_lock()) {}
- }
-
- // Atomically unlock the write-lock from writer and acquire the read-lock.
- void unlock_and_lock_shared() {
- QuarterInt val = __sync_fetch_and_add(&ticket.read, 1);
- }
-
- // Release writer permission on the lock.
- void unlock() {
- RWTicket t;
- t.whole = load_acquire(&ticket.whole);
-
-#ifdef RW_SPINLOCK_USE_SSE_INSTRUCTIONS_
- FullInt old = t.whole;
- // SSE2 can reduce the lock and unlock overhead by 10%
- static const QuarterInt kDeltaBuf[4] = { 1, 1, 0, 0 }; // write/read/user
- static const __m128i kDelta = IntTraitType::make128(kDeltaBuf);
- __m128i m = IntTraitType::fromInteger(old);
- t.whole = IntTraitType::addParallel(m, kDelta);
-#else
- ++t.read;
- ++t.write;
-#endif
- store_release(&ticket.readWrite, t.readWrite);
- }
-
- void lock_shared() {
- // std::this_thread::yield() is important here because we can't grab the
- // shared lock if there is a pending writeLockAggressive, so we
- // need to let threads that already have a shared lock complete
- uint_fast32_t count = 0;
- while (!LIKELY(try_lock_shared())) {
- asm_volatile_pause();
- if (UNLIKELY((++count & 1023) == 0)) {
- std::this_thread::yield();
- }
- }
- }
-
- bool try_lock_shared() {
- RWTicket t, old;
- old.whole = t.whole = load_acquire(&ticket.whole);
- old.users = old.read;
-#ifdef RW_SPINLOCK_USE_SSE_INSTRUCTIONS_
- // SSE2 may reduce the total lock and unlock overhead by 10%
- static const QuarterInt kDeltaBuf[4] = { 0, 1, 1, 0 }; // write/read/user
- static const __m128i kDelta = IntTraitType::make128(kDeltaBuf);
- __m128i m = IntTraitType::fromInteger(old.whole);
- t.whole = IntTraitType::addParallel(m, kDelta);
-#else
- ++t.read;
- ++t.users;
-#endif
- return __sync_bool_compare_and_swap(&ticket.whole, old.whole, t.whole);
- }
-
- void unlock_shared() {
- __sync_fetch_and_add(&ticket.write, 1);
- }
-
- class WriteHolder;
-
- typedef RWTicketSpinLockT<kBitWidth, kFavorWriter> RWSpinLock;
- class ReadHolder {
- public:
- ReadHolder(ReadHolder const&) = delete;
- ReadHolder& operator=(ReadHolder const&) = delete;
-
- explicit ReadHolder(RWSpinLock* lock) : lock_(lock) {
- if (lock_) {
- lock_->lock_shared();
- }
- }
-
- explicit ReadHolder(RWSpinLock &lock) : lock_ (&lock) {
- if (lock_) {
- lock_->lock_shared();
- }
- }
-
- // atomically unlock the write-lock from writer and acquire the read-lock
- explicit ReadHolder(WriteHolder *writer) : lock_(nullptr) {
- std::swap(this->lock_, writer->lock_);
- if (lock_) {
- lock_->unlock_and_lock_shared();
- }
- }
-
- ~ReadHolder() {
- if (lock_) {
- lock_->unlock_shared();
- }
- }
-
- void reset(RWSpinLock *lock = nullptr) {
- if (lock_) {
- lock_->unlock_shared();
- }
- lock_ = lock;
- if (lock_) {
- lock_->lock_shared();
- }
- }
-
- void swap(ReadHolder *other) {
- std::swap(this->lock_, other->lock_);
- }
-
- private:
- RWSpinLock *lock_;
- };
-
- class WriteHolder {
- public:
- WriteHolder(WriteHolder const&) = delete;
- WriteHolder& operator=(WriteHolder const&) = delete;
-
- explicit WriteHolder(RWSpinLock* lock) : lock_(lock) {
- if (lock_) {
- lock_->lock();
- }
- }
- explicit WriteHolder(RWSpinLock &lock) : lock_ (&lock) {
- if (lock_) {
- lock_->lock();
- }
- }
-
- ~WriteHolder() {
- if (lock_) {
- lock_->unlock();
- }
- }
-
- void reset(RWSpinLock *lock = nullptr) {
- if (lock == lock_) {
- return;
- }
- if (lock_) {
- lock_->unlock();
- }
- lock_ = lock;
- if (lock_) {
- lock_->lock();
- }
- }
-
- void swap(WriteHolder *other) {
- std::swap(this->lock_, other->lock_);
- }
-
- private:
- friend class ReadHolder;
- RWSpinLock *lock_;
- };
-};
-
-typedef RWTicketSpinLockT<32> RWTicketSpinLock32;
-typedef RWTicketSpinLockT<64> RWTicketSpinLock64;
-
-#endif // RW_SPINLOCK_USE_X86_INTRINSIC_
-
-} // namespace folly
-
-#ifdef RW_SPINLOCK_USE_X86_INTRINSIC_
-#undef RW_SPINLOCK_USE_X86_INTRINSIC_
-#endif
+#include <folly/synchronization/RWSpinLock.h> // @shim
projects / folly.git / blobdiff