mirror of https://github.com/grpc/grpc.git
[EventEngine] Improve lock contention in WorkStealingThreadPool (alternative) (#34065)
Proposed alternative to https://github.com/grpc/grpc/pull/34024. This version has a simpler, faster busy-count implementation based on a sharded set of atomic counts: fast increment/decrement operations, relatively slower summation of total counts (which need to happen much less frequently).pull/33175/head
AJ Heller
1 year ago
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GitHub
parent
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commit
108af0a94f
21 changed files with 489 additions and 153 deletions
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// Copyright 2023 The gRPC Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include <grpc/support/port_platform.h> |
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#include "src/core/lib/event_engine/thread_pool/thread_count.h" |
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#include <inttypes.h> |
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#include "absl/time/clock.h" |
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#include "absl/time/time.h" |
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#include <grpc/support/log.h> |
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namespace grpc_event_engine { |
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namespace experimental { |
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// -------- LivingThreadCount --------
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void LivingThreadCount::BlockUntilThreadCount(size_t desired_threads, |
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const char* why) { |
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constexpr grpc_core::Duration log_rate = grpc_core::Duration::Seconds(3); |
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while (true) { |
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auto curr_threads = WaitForCountChange(desired_threads, log_rate); |
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if (curr_threads == desired_threads) break; |
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GRPC_LOG_EVERY_N_SEC_DELAYED( |
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log_rate.seconds(), GPR_DEBUG, |
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"Waiting for thread pool to idle before %s. (%" PRIdPTR " to %" PRIdPTR |
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")", |
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why, curr_threads, desired_threads); |
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} |
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} |
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size_t LivingThreadCount::WaitForCountChange(size_t desired_threads, |
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grpc_core::Duration timeout) { |
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size_t count; |
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auto deadline = absl::Now() + absl::Milliseconds(timeout.millis()); |
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do { |
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grpc_core::MutexLock lock(&mu_); |
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count = CountLocked(); |
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if (count == desired_threads) break; |
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cv_.WaitWithDeadline(&mu_, deadline); |
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} while (absl::Now() < deadline); |
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return count; |
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} |
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} // namespace experimental
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} // namespace grpc_event_engine
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// Copyright 2023 The gRPC Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef GRPC_SRC_CORE_LIB_EVENT_ENGINE_THREAD_POOL_THREAD_COUNT_H |
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#define GRPC_SRC_CORE_LIB_EVENT_ENGINE_THREAD_POOL_THREAD_COUNT_H |
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#include <grpc/support/port_platform.h> |
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#include <atomic> |
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#include <cstddef> |
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#include <numeric> |
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#include <utility> |
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#include <vector> |
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#include "absl/base/thread_annotations.h" |
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#include <grpc/support/cpu.h> |
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#include "src/core/lib/gpr/useful.h" |
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#include "src/core/lib/gprpp/sync.h" |
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#include "src/core/lib/gprpp/time.h" |
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namespace grpc_event_engine { |
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namespace experimental { |
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// Tracks counts across some fixed number of shards.
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// It is intended for fast increment/decrement operations, but a slower overall
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// count operation.
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class BusyThreadCount { |
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public: |
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// Increments a per-shard counter on construction, decrements on destruction.
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class AutoThreadCounter { |
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public: |
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AutoThreadCounter(BusyThreadCount* counter, size_t idx) |
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: counter_(counter), idx_(idx) { |
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counter_->Increment(idx_); |
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} |
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~AutoThreadCounter() { |
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if (counter_ != nullptr) counter_->Decrement(idx_); |
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} |
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// not copyable
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AutoThreadCounter(const AutoThreadCounter&) = delete; |
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AutoThreadCounter& operator=(const AutoThreadCounter&) = delete; |
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// moveable
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AutoThreadCounter(AutoThreadCounter&& other) noexcept { |
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counter_ = std::exchange(other.counter_, nullptr); |
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idx_ = other.idx_; |
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} |
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AutoThreadCounter& operator=(AutoThreadCounter&& other) noexcept { |
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counter_ = std::exchange(other.counter_, nullptr); |
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idx_ = other.idx_; |
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return *this; |
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} |
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private: |
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BusyThreadCount* counter_; |
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size_t idx_; |
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}; |
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BusyThreadCount() : shards_(grpc_core::Clamp(gpr_cpu_num_cores(), 2u, 64u)) {} |
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AutoThreadCounter MakeAutoThreadCounter(size_t idx) { |
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return AutoThreadCounter(this, idx); |
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}; |
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void Increment(size_t idx) { |
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shards_[idx].busy_count.fetch_add(1, std::memory_order_relaxed); |
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} |
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void Decrement(size_t idx) { |
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shards_[idx].busy_count.fetch_sub(1, std::memory_order_relaxed); |
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} |
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size_t count() { |
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return std::accumulate( |
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shards_.begin(), shards_.end(), 0, [](size_t running, ShardedData& d) { |
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return running + d.busy_count.load(std::memory_order_relaxed); |
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}); |
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} |
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// Returns some valid index into the per-shard data, which is rotated on every
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// call to distribute load and reduce contention.
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size_t NextIndex() { return next_idx_.fetch_add(1) % shards_.size(); } |
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private: |
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struct ShardedData { |
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std::atomic<size_t> busy_count{0}; |
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} GPR_ALIGN_STRUCT(GPR_CACHELINE_SIZE); |
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std::vector<ShardedData> shards_; |
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std::atomic<size_t> next_idx_{0}; |
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}; |
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// Tracks the number of living threads. It is intended for a fast count
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// operation, with relatively slower increment/decrement operations.
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class LivingThreadCount { |
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public: |
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// Increments the global counter on construction, decrements on destruction.
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class AutoThreadCounter { |
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public: |
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explicit AutoThreadCounter(LivingThreadCount* counter) : counter_(counter) { |
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counter_->Increment(); |
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} |
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~AutoThreadCounter() { |
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if (counter_ != nullptr) counter_->Decrement(); |
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} |
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// not copyable
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AutoThreadCounter(const AutoThreadCounter&) = delete; |
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AutoThreadCounter& operator=(const AutoThreadCounter&) = delete; |
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// moveable
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AutoThreadCounter(AutoThreadCounter&& other) noexcept { |
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counter_ = std::exchange(other.counter_, nullptr); |
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} |
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AutoThreadCounter& operator=(AutoThreadCounter&& other) noexcept { |
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counter_ = std::exchange(other.counter_, nullptr); |
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return *this; |
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} |
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private: |
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LivingThreadCount* counter_; |
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}; |
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AutoThreadCounter MakeAutoThreadCounter() { return AutoThreadCounter(this); }; |
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void Increment() ABSL_LOCKS_EXCLUDED(mu_) { |
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grpc_core::MutexLock lock(&mu_); |
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++living_count_; |
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cv_.SignalAll(); |
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} |
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void Decrement() ABSL_LOCKS_EXCLUDED(mu_) { |
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grpc_core::MutexLock lock(&mu_); |
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--living_count_; |
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cv_.SignalAll(); |
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} |
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void BlockUntilThreadCount(size_t desired_threads, const char* why) |
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ABSL_LOCKS_EXCLUDED(mu_); |
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size_t count() ABSL_LOCKS_EXCLUDED(mu_) { |
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grpc_core::MutexLock lock(&mu_); |
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return CountLocked(); |
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} |
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private: |
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size_t CountLocked() ABSL_EXCLUSIVE_LOCKS_REQUIRED(mu_) { |
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return living_count_; |
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} |
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size_t WaitForCountChange(size_t desired_threads, |
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grpc_core::Duration timeout); |
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grpc_core::Mutex mu_; |
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grpc_core::CondVar cv_ ABSL_GUARDED_BY(mu_); |
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size_t living_count_ ABSL_GUARDED_BY(mu_) = 0; |
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}; |
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} // namespace experimental
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} // namespace grpc_event_engine
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#endif // GRPC_SRC_CORE_LIB_EVENT_ENGINE_THREAD_POOL_THREAD_COUNT_H
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