stdcpp_waiter.cc (2608B)
1 // Copyright 2023 The Abseil Authors. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 #include "absl/synchronization/internal/stdcpp_waiter.h" 16 17 #ifdef ABSL_INTERNAL_HAVE_STDCPP_WAITER 18 19 #include <chrono> // NOLINT(build/c++11) 20 #include <condition_variable> // NOLINT(build/c++11) 21 #include <mutex> // NOLINT(build/c++11) 22 23 #include "absl/base/config.h" 24 #include "absl/base/internal/raw_logging.h" 25 #include "absl/base/internal/thread_identity.h" 26 #include "absl/base/optimization.h" 27 #include "absl/synchronization/internal/kernel_timeout.h" 28 29 namespace absl { 30 ABSL_NAMESPACE_BEGIN 31 namespace synchronization_internal { 32 33 StdcppWaiter::StdcppWaiter() : waiter_count_(0), wakeup_count_(0) {} 34 35 bool StdcppWaiter::Wait(KernelTimeout t) { 36 std::unique_lock<std::mutex> lock(mu_); 37 ++waiter_count_; 38 39 // Loop until we find a wakeup to consume or timeout. 40 // Note that, since the thread ticker is just reset, we don't need to check 41 // whether the thread is idle on the very first pass of the loop. 42 bool first_pass = true; 43 while (wakeup_count_ == 0) { 44 if (!first_pass) MaybeBecomeIdle(); 45 // No wakeups available, time to wait. 46 if (!t.has_timeout()) { 47 cv_.wait(lock); 48 } else { 49 auto wait_result = t.SupportsSteadyClock() && t.is_relative_timeout() 50 ? cv_.wait_for(lock, t.ToChronoDuration()) 51 : cv_.wait_until(lock, t.ToChronoTimePoint()); 52 if (wait_result == std::cv_status::timeout) { 53 --waiter_count_; 54 return false; 55 } 56 } 57 first_pass = false; 58 } 59 60 // Consume a wakeup and we're done. 61 --wakeup_count_; 62 --waiter_count_; 63 return true; 64 } 65 66 void StdcppWaiter::Post() { 67 std::lock_guard<std::mutex> lock(mu_); 68 ++wakeup_count_; 69 InternalCondVarPoke(); 70 } 71 72 void StdcppWaiter::Poke() { 73 std::lock_guard<std::mutex> lock(mu_); 74 InternalCondVarPoke(); 75 } 76 77 void StdcppWaiter::InternalCondVarPoke() { 78 if (waiter_count_ != 0) { 79 cv_.notify_one(); 80 } 81 } 82 83 } // namespace synchronization_internal 84 ABSL_NAMESPACE_END 85 } // namespace absl 86 87 #endif // ABSL_INTERNAL_HAVE_STDCPP_WAITER