diff options
Diffstat (limited to 'third_party/abseil_cpp/absl/base/internal/spinlock.cc')
| -rw-r--r-- | third_party/abseil_cpp/absl/base/internal/spinlock.cc | 220 |
1 files changed, 0 insertions, 220 deletions
diff --git a/third_party/abseil_cpp/absl/base/internal/spinlock.cc b/third_party/abseil_cpp/absl/base/internal/spinlock.cc deleted file mode 100644 index a7d44f3eb091..000000000000 --- a/third_party/abseil_cpp/absl/base/internal/spinlock.cc +++ /dev/null @@ -1,220 +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. - -#include "absl/base/internal/spinlock.h" - -#include <algorithm> -#include <atomic> -#include <limits> - -#include "absl/base/attributes.h" -#include "absl/base/internal/atomic_hook.h" -#include "absl/base/internal/cycleclock.h" -#include "absl/base/internal/spinlock_wait.h" -#include "absl/base/internal/sysinfo.h" /* For NumCPUs() */ -#include "absl/base/call_once.h" - -// Description of lock-word: -// 31..00: [............................3][2][1][0] -// -// [0]: kSpinLockHeld -// [1]: kSpinLockCooperative -// [2]: kSpinLockDisabledScheduling -// [31..3]: ONLY kSpinLockSleeper OR -// Wait time in cycles >> PROFILE_TIMESTAMP_SHIFT -// -// Detailed descriptions: -// -// Bit [0]: The lock is considered held iff kSpinLockHeld is set. -// -// Bit [1]: Eligible waiters (e.g. Fibers) may co-operatively reschedule when -// contended iff kSpinLockCooperative is set. -// -// Bit [2]: This bit is exclusive from bit [1]. It is used only by a -// non-cooperative lock. When set, indicates that scheduling was -// successfully disabled when the lock was acquired. May be unset, -// even if non-cooperative, if a ThreadIdentity did not yet exist at -// time of acquisition. -// -// Bit [3]: If this is the only upper bit ([31..3]) set then this lock was -// acquired without contention, however, at least one waiter exists. -// -// Otherwise, bits [31..3] represent the time spent by the current lock -// holder to acquire the lock. There may be outstanding waiter(s). - -namespace absl { -ABSL_NAMESPACE_BEGIN -namespace base_internal { - -ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES static base_internal::AtomicHook<void (*)( - const void *lock, int64_t wait_cycles)> - submit_profile_data; - -void RegisterSpinLockProfiler(void (*fn)(const void *contendedlock, - int64_t wait_cycles)) { - submit_profile_data.Store(fn); -} - -// Static member variable definitions. -constexpr uint32_t SpinLock::kSpinLockHeld; -constexpr uint32_t SpinLock::kSpinLockCooperative; -constexpr uint32_t SpinLock::kSpinLockDisabledScheduling; -constexpr uint32_t SpinLock::kSpinLockSleeper; -constexpr uint32_t SpinLock::kWaitTimeMask; - -// Uncommon constructors. -SpinLock::SpinLock(base_internal::SchedulingMode mode) - : lockword_(IsCooperative(mode) ? kSpinLockCooperative : 0) { - ABSL_TSAN_MUTEX_CREATE(this, __tsan_mutex_not_static); -} - -// Monitor the lock to see if its value changes within some time period -// (adaptive_spin_count loop iterations). The last value read from the lock -// is returned from the method. -uint32_t SpinLock::SpinLoop() { - // We are already in the slow path of SpinLock, initialize the - // adaptive_spin_count here. - ABSL_CONST_INIT static absl::once_flag init_adaptive_spin_count; - ABSL_CONST_INIT static int adaptive_spin_count = 0; - base_internal::LowLevelCallOnce(&init_adaptive_spin_count, []() { - adaptive_spin_count = base_internal::NumCPUs() > 1 ? 1000 : 1; - }); - - int c = adaptive_spin_count; - uint32_t lock_value; - do { - lock_value = lockword_.load(std::memory_order_relaxed); - } while ((lock_value & kSpinLockHeld) != 0 && --c > 0); - return lock_value; -} - -void SpinLock::SlowLock() { - uint32_t lock_value = SpinLoop(); - lock_value = TryLockInternal(lock_value, 0); - if ((lock_value & kSpinLockHeld) == 0) { - return; - } - - base_internal::SchedulingMode scheduling_mode; - if ((lock_value & kSpinLockCooperative) != 0) { - scheduling_mode = base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL; - } else { - scheduling_mode = base_internal::SCHEDULE_KERNEL_ONLY; - } - - // The lock was not obtained initially, so this thread needs to wait for - // it. Record the current timestamp in the local variable wait_start_time - // so the total wait time can be stored in the lockword once this thread - // obtains the lock. - int64_t wait_start_time = CycleClock::Now(); - uint32_t wait_cycles = 0; - int lock_wait_call_count = 0; - while ((lock_value & kSpinLockHeld) != 0) { - // If the lock is currently held, but not marked as having a sleeper, mark - // it as having a sleeper. - if ((lock_value & kWaitTimeMask) == 0) { - // Here, just "mark" that the thread is going to sleep. Don't store the - // lock wait time in the lock as that will cause the current lock - // owner to think it experienced contention. - if (lockword_.compare_exchange_strong( - lock_value, lock_value | kSpinLockSleeper, - std::memory_order_relaxed, std::memory_order_relaxed)) { - // Successfully transitioned to kSpinLockSleeper. Pass - // kSpinLockSleeper to the SpinLockWait routine to properly indicate - // the last lock_value observed. - lock_value |= kSpinLockSleeper; - } else if ((lock_value & kSpinLockHeld) == 0) { - // Lock is free again, so try and acquire it before sleeping. The - // new lock state will be the number of cycles this thread waited if - // this thread obtains the lock. - lock_value = TryLockInternal(lock_value, wait_cycles); - continue; // Skip the delay at the end of the loop. - } - } - - // SpinLockDelay() calls into fiber scheduler, we need to see - // synchronization there to avoid false positives. - ABSL_TSAN_MUTEX_PRE_DIVERT(this, 0); - // Wait for an OS specific delay. - base_internal::SpinLockDelay(&lockword_, lock_value, ++lock_wait_call_count, - scheduling_mode); - ABSL_TSAN_MUTEX_POST_DIVERT(this, 0); - // Spin again after returning from the wait routine to give this thread - // some chance of obtaining the lock. - lock_value = SpinLoop(); - wait_cycles = EncodeWaitCycles(wait_start_time, CycleClock::Now()); - lock_value = TryLockInternal(lock_value, wait_cycles); - } -} - -void SpinLock::SlowUnlock(uint32_t lock_value) { - base_internal::SpinLockWake(&lockword_, - false); // wake waiter if necessary - - // If our acquisition was contended, collect contentionz profile info. We - // reserve a unitary wait time to represent that a waiter exists without our - // own acquisition having been contended. - if ((lock_value & kWaitTimeMask) != kSpinLockSleeper) { - const uint64_t wait_cycles = DecodeWaitCycles(lock_value); - ABSL_TSAN_MUTEX_PRE_DIVERT(this, 0); - submit_profile_data(this, wait_cycles); - ABSL_TSAN_MUTEX_POST_DIVERT(this, 0); - } -} - -// We use the upper 29 bits of the lock word to store the time spent waiting to -// acquire this lock. This is reported by contentionz profiling. Since the -// lower bits of the cycle counter wrap very quickly on high-frequency -// processors we divide to reduce the granularity to 2^kProfileTimestampShift -// sized units. On a 4Ghz machine this will lose track of wait times greater -// than (2^29/4 Ghz)*128 =~ 17.2 seconds. Such waits should be extremely rare. -static constexpr int kProfileTimestampShift = 7; - -// We currently reserve the lower 3 bits. -static constexpr int kLockwordReservedShift = 3; - -uint32_t SpinLock::EncodeWaitCycles(int64_t wait_start_time, - int64_t wait_end_time) { - static const int64_t kMaxWaitTime = - std::numeric_limits<uint32_t>::max() >> kLockwordReservedShift; - int64_t scaled_wait_time = - (wait_end_time - wait_start_time) >> kProfileTimestampShift; - - // Return a representation of the time spent waiting that can be stored in - // the lock word's upper bits. - uint32_t clamped = static_cast<uint32_t>( - std::min(scaled_wait_time, kMaxWaitTime) << kLockwordReservedShift); - - if (clamped == 0) { - return kSpinLockSleeper; // Just wake waiters, but don't record contention. - } - // Bump up value if necessary to avoid returning kSpinLockSleeper. - const uint32_t kMinWaitTime = - kSpinLockSleeper + (1 << kLockwordReservedShift); - if (clamped == kSpinLockSleeper) { - return kMinWaitTime; - } - return clamped; -} - -uint64_t SpinLock::DecodeWaitCycles(uint32_t lock_value) { - // Cast to uint32_t first to ensure bits [63:32] are cleared. - const uint64_t scaled_wait_time = - static_cast<uint32_t>(lock_value & kWaitTimeMask); - return scaled_wait_time << (kProfileTimestampShift - kLockwordReservedShift); -} - -} // namespace base_internal -ABSL_NAMESPACE_END -} // namespace absl |