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Diffstat (limited to 'third_party/abseil_cpp/absl/base/internal/spinlock.h')
| -rw-r--r-- | third_party/abseil_cpp/absl/base/internal/spinlock.h | 230 |
1 files changed, 0 insertions, 230 deletions
diff --git a/third_party/abseil_cpp/absl/base/internal/spinlock.h b/third_party/abseil_cpp/absl/base/internal/spinlock.h deleted file mode 100644 index 2222398b16..0000000000 --- a/third_party/abseil_cpp/absl/base/internal/spinlock.h +++ /dev/null @@ -1,230 +0,0 @@ -// -// Copyright 2017 The Abseil Authors. -// -// Licensed under the Apache License, Version 2.0 (the "License"); -// you may not use this file except in compliance with the License. -// You may obtain a copy of the License at -// -// https://www.apache.org/licenses/LICENSE-2.0 -// -// Unless required by applicable law or agreed to in writing, software -// distributed under the License is distributed on an "AS IS" BASIS, -// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. -// See the License for the specific language governing permissions and -// limitations under the License. -// - -// Most users requiring mutual exclusion should use Mutex. -// SpinLock is provided for use in three situations: -// - for use in code that Mutex itself depends on -// - to get a faster fast-path release under low contention (without an -// atomic read-modify-write) In return, SpinLock has worse behaviour under -// contention, which is why Mutex is preferred in most situations. -// - for async signal safety (see below) - -// SpinLock is async signal safe. If a spinlock is used within a signal -// handler, all code that acquires the lock must ensure that the signal cannot -// arrive while they are holding the lock. Typically, this is done by blocking -// the signal. - -#ifndef ABSL_BASE_INTERNAL_SPINLOCK_H_ -#define ABSL_BASE_INTERNAL_SPINLOCK_H_ - -#include <stdint.h> -#include <sys/types.h> - -#include <atomic> - -#include "absl/base/attributes.h" -#include "absl/base/const_init.h" -#include "absl/base/dynamic_annotations.h" -#include "absl/base/internal/low_level_scheduling.h" -#include "absl/base/internal/raw_logging.h" -#include "absl/base/internal/scheduling_mode.h" -#include "absl/base/internal/tsan_mutex_interface.h" -#include "absl/base/macros.h" -#include "absl/base/port.h" -#include "absl/base/thread_annotations.h" - -namespace absl { -ABSL_NAMESPACE_BEGIN -namespace base_internal { - -class ABSL_LOCKABLE SpinLock { - public: - SpinLock() : lockword_(kSpinLockCooperative) { - ABSL_TSAN_MUTEX_CREATE(this, __tsan_mutex_not_static); - } - - // Constructors that allow non-cooperative spinlocks to be created for use - // inside thread schedulers. Normal clients should not use these. - explicit SpinLock(base_internal::SchedulingMode mode); - - // Constructor for global SpinLock instances. See absl/base/const_init.h. - constexpr SpinLock(absl::ConstInitType, base_internal::SchedulingMode mode) - : lockword_(IsCooperative(mode) ? kSpinLockCooperative : 0) {} - - ~SpinLock() { ABSL_TSAN_MUTEX_DESTROY(this, __tsan_mutex_not_static); } - - // Acquire this SpinLock. - inline void Lock() ABSL_EXCLUSIVE_LOCK_FUNCTION() { - ABSL_TSAN_MUTEX_PRE_LOCK(this, 0); - if (!TryLockImpl()) { - SlowLock(); - } - ABSL_TSAN_MUTEX_POST_LOCK(this, 0, 0); - } - - // Try to acquire this SpinLock without blocking and return true if the - // acquisition was successful. If the lock was not acquired, false is - // returned. If this SpinLock is free at the time of the call, TryLock - // will return true with high probability. - inline bool TryLock() ABSL_EXCLUSIVE_TRYLOCK_FUNCTION(true) { - ABSL_TSAN_MUTEX_PRE_LOCK(this, __tsan_mutex_try_lock); - bool res = TryLockImpl(); - ABSL_TSAN_MUTEX_POST_LOCK( - this, __tsan_mutex_try_lock | (res ? 0 : __tsan_mutex_try_lock_failed), - 0); - return res; - } - - // Release this SpinLock, which must be held by the calling thread. - inline void Unlock() ABSL_UNLOCK_FUNCTION() { - ABSL_TSAN_MUTEX_PRE_UNLOCK(this, 0); - uint32_t lock_value = lockword_.load(std::memory_order_relaxed); - lock_value = lockword_.exchange(lock_value & kSpinLockCooperative, - std::memory_order_release); - - if ((lock_value & kSpinLockDisabledScheduling) != 0) { - base_internal::SchedulingGuard::EnableRescheduling(true); - } - if ((lock_value & kWaitTimeMask) != 0) { - // Collect contentionz profile info, and speed the wakeup of any waiter. - // The wait_cycles value indicates how long this thread spent waiting - // for the lock. - SlowUnlock(lock_value); - } - ABSL_TSAN_MUTEX_POST_UNLOCK(this, 0); - } - - // Determine if the lock is held. When the lock is held by the invoking - // thread, true will always be returned. Intended to be used as - // CHECK(lock.IsHeld()). - inline bool IsHeld() const { - return (lockword_.load(std::memory_order_relaxed) & kSpinLockHeld) != 0; - } - - protected: - // These should not be exported except for testing. - - // Store number of cycles between wait_start_time and wait_end_time in a - // lock value. - static uint32_t EncodeWaitCycles(int64_t wait_start_time, - int64_t wait_end_time); - - // Extract number of wait cycles in a lock value. - static uint64_t DecodeWaitCycles(uint32_t lock_value); - - // Provide access to protected method above. Use for testing only. - friend struct SpinLockTest; - - private: - // lockword_ is used to store the following: - // - // bit[0] encodes whether a lock is being held. - // bit[1] encodes whether a lock uses cooperative scheduling. - // bit[2] encodes whether a lock disables scheduling. - // bit[3:31] encodes time a lock spent on waiting as a 29-bit unsigned int. - static constexpr uint32_t kSpinLockHeld = 1; - static constexpr uint32_t kSpinLockCooperative = 2; - static constexpr uint32_t kSpinLockDisabledScheduling = 4; - static constexpr uint32_t kSpinLockSleeper = 8; - // Includes kSpinLockSleeper. - static constexpr uint32_t kWaitTimeMask = - ~(kSpinLockHeld | kSpinLockCooperative | kSpinLockDisabledScheduling); - - // Returns true if the provided scheduling mode is cooperative. - static constexpr bool IsCooperative( - base_internal::SchedulingMode scheduling_mode) { - return scheduling_mode == base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL; - } - - uint32_t TryLockInternal(uint32_t lock_value, uint32_t wait_cycles); - void SlowLock() ABSL_ATTRIBUTE_COLD; - void SlowUnlock(uint32_t lock_value) ABSL_ATTRIBUTE_COLD; - uint32_t SpinLoop(); - - inline bool TryLockImpl() { - uint32_t lock_value = lockword_.load(std::memory_order_relaxed); - return (TryLockInternal(lock_value, 0) & kSpinLockHeld) == 0; - } - - std::atomic<uint32_t> lockword_; - - SpinLock(const SpinLock&) = delete; - SpinLock& operator=(const SpinLock&) = delete; -}; - -// Corresponding locker object that arranges to acquire a spinlock for -// the duration of a C++ scope. -class ABSL_SCOPED_LOCKABLE SpinLockHolder { - public: - inline explicit SpinLockHolder(SpinLock* l) ABSL_EXCLUSIVE_LOCK_FUNCTION(l) - : lock_(l) { - l->Lock(); - } - inline ~SpinLockHolder() ABSL_UNLOCK_FUNCTION() { lock_->Unlock(); } - - SpinLockHolder(const SpinLockHolder&) = delete; - SpinLockHolder& operator=(const SpinLockHolder&) = delete; - - private: - SpinLock* lock_; -}; - -// Register a hook for profiling support. -// -// The function pointer registered here will be called whenever a spinlock is -// contended. The callback is given an opaque handle to the contended spinlock -// and the number of wait cycles. This is thread-safe, but only a single -// profiler can be registered. It is an error to call this function multiple -// times with different arguments. -void RegisterSpinLockProfiler(void (*fn)(const void* lock, - int64_t wait_cycles)); - -//------------------------------------------------------------------------------ -// Public interface ends here. -//------------------------------------------------------------------------------ - -// If (result & kSpinLockHeld) == 0, then *this was successfully locked. -// Otherwise, returns last observed value for lockword_. -inline uint32_t SpinLock::TryLockInternal(uint32_t lock_value, - uint32_t wait_cycles) { - if ((lock_value & kSpinLockHeld) != 0) { - return lock_value; - } - - uint32_t sched_disabled_bit = 0; - if ((lock_value & kSpinLockCooperative) == 0) { - // For non-cooperative locks we must make sure we mark ourselves as - // non-reschedulable before we attempt to CompareAndSwap. - if (base_internal::SchedulingGuard::DisableRescheduling()) { - sched_disabled_bit = kSpinLockDisabledScheduling; - } - } - - if (!lockword_.compare_exchange_strong( - lock_value, - kSpinLockHeld | lock_value | wait_cycles | sched_disabled_bit, - std::memory_order_acquire, std::memory_order_relaxed)) { - base_internal::SchedulingGuard::EnableRescheduling(sched_disabled_bit != 0); - } - - return lock_value; -} - -} // namespace base_internal -ABSL_NAMESPACE_END -} // namespace absl - -#endif // ABSL_BASE_INTERNAL_SPINLOCK_H_ |