1 // 2 // 3 // Copyright 2017 gRPC authors. 4 // 5 // Licensed under the Apache License, Version 2.0 (the "License"); 6 // you may not use this file except in compliance with the License. 7 // You may obtain a copy of the License at 8 // 9 // http://www.apache.org/licenses/LICENSE-2.0 10 // 11 // Unless required by applicable law or agreed to in writing, software 12 // distributed under the License is distributed on an "AS IS" BASIS, 13 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 // See the License for the specific language governing permissions and 15 // limitations under the License. 16 // 17 // 18 19 #ifndef GRPC_SRC_CORE_LIB_GPRPP_ATOMIC_UTILS_H 20 #define GRPC_SRC_CORE_LIB_GPRPP_ATOMIC_UTILS_H 21 22 #include <grpc/support/port_platform.h> 23 24 #include <atomic> 25 26 namespace grpc_core { 27 28 // Atomically increment a counter only if the counter value is not zero. 29 // Returns true if increment took place; false if counter is zero. 30 template <typename T> IncrementIfNonzero(std::atomic<T> * p)31inline bool IncrementIfNonzero(std::atomic<T>* p) { 32 T count = p->load(std::memory_order_acquire); 33 do { 34 // If zero, we are done (without an increment). If not, we must do a CAS 35 // to maintain the contract: do not increment the counter if it is already 36 // zero 37 if (count == 0) { 38 return false; 39 } 40 } while (!p->compare_exchange_weak( 41 count, count + 1, std::memory_order_acq_rel, std::memory_order_acquire)); 42 return true; 43 } 44 45 } // namespace grpc_core 46 47 #endif // GRPC_SRC_CORE_LIB_GPRPP_ATOMIC_UTILS_H 48