| // Copyright 2022 The Pigweed 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 "pw_intrusive_ptr/internal/ref_counted_base.h" |
| |
| #include <atomic> |
| #include <cstdint> |
| |
| #include "pw_assert/check.h" |
| |
| namespace pw::internal { |
| |
| RefCountedBase::~RefCountedBase() { |
| // Set the ref count to a poison value so that we have the best chance of |
| // catching a use-after-free situation. |
| // |
| // The value is chosen specifically to be negative when stored as an int32_t, |
| // and as far away from becoming positive (via either addition or subtraction) |
| // as possible. |
| ref_count_.store(static_cast<int32_t>(0xC0000000), std::memory_order_release); |
| } |
| |
| void RefCountedBase::AddRef() const { |
| const auto refs = ref_count_.fetch_add(1, std::memory_order_relaxed); |
| |
| // This assertion will fire if someone calls AddRef() on a ref-counted object |
| // that has reached ref_count_ == 0 but has not been destroyed yet. This could |
| // happen by manually calling AddRef(), or re-wrapping such a pointer with |
| // RefPtr<T>(T*) (which calls AddRef()). |
| PW_DCHECK(refs >= 0); |
| } |
| |
| bool RefCountedBase::ReleaseRef() const { |
| // We don't follow the boost::intrusive_ptr/fit::RefPtr approach here with a |
| // release fetch_sub and acquire fence afterwards due to TSAN not supporting |
| // fences (see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97868). |
| // |
| // This approach is a bit less performant - it does the acquiring on each |
| // release, not only for the last ref - but otherwise works the same. |
| const auto refs = ref_count_.fetch_sub(1, std::memory_order_acq_rel); |
| |
| // This assertion will fire if someone manually calls ReleaseRef() |
| // on a ref-counted object too many times, or if ReleaseRef is called |
| // before an object has been wrapped with RefPtr. |
| PW_DCHECK(refs >= 1); |
| |
| return refs == 1; |
| } |
| |
| } // namespace pw::internal |