atomic_utils.h

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/*
 *
 * Copyright 2017 gRPC 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
 *
 *     http://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.
 *
 */
 
#ifndef GRPC_CORE_LIB_GPRPP_ATOMIC_UTILS_H
#define GRPC_CORE_LIB_GPRPP_ATOMIC_UTILS_H
 
#include <grpc/support/port_platform.h>
 
#include <atomic>
 
namespace grpc_core {
 
// Atomically increment a counter only if the counter value is not zero.
// Returns true if increment took place; false if counter is zero.
template <typename T>
inline bool IncrementIfNonzero(std::atomic<T>* p) {
  T count = p->load(std::memory_order_acquire);
  do {
    // If zero, we are done (without an increment). If not, we must do a CAS
    // to maintain the contract: do not increment the counter if it is already
    // zero
    if (count == 0) {
      return false;
    }
  } while (!p->compare_exchange_weak(
      count, count + 1, std::memory_order_acq_rel, std::memory_order_acquire));
  return true;
}
 
}  // namespace grpc_core
 
#endif /* GRPC_CORE_LIB_GPRPP_ATOMIC_UTILS_H */