62 lines
2.3 KiB
C++
62 lines
2.3 KiB
C++
// Copyright 2022 The Pigweed Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may not
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// use this file except in compliance with the License. You may obtain a copy of
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// the License at
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//
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// https://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, WITHOUT
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// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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// License for the specific language governing permissions and limitations under
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// the License.
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#include "pw_intrusive_ptr/internal/ref_counted_base.h"
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#include <atomic>
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#include <cstdint>
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#include "pw_assert/check.h"
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namespace pw::internal {
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RefCountedBase::~RefCountedBase() {
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// Set the ref count to a poison value so that we have the best chance of
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// catching a use-after-free situation.
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//
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// The value is chosen specifically to be negative when stored as an int32_t,
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// and as far away from becoming positive (via either addition or subtraction)
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// as possible.
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ref_count_.store(static_cast<int32_t>(0xC0000000), std::memory_order_release);
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}
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void RefCountedBase::AddRef() const {
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const auto refs = ref_count_.fetch_add(1, std::memory_order_relaxed);
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// This assertion will fire if someone calls AddRef() on a ref-counted object
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// that has reached ref_count_ == 0 but has not been destroyed yet. This could
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// happen by manually calling AddRef(), or re-wrapping such a pointer with
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// RefPtr<T>(T*) (which calls AddRef()).
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PW_DCHECK(refs >= 0);
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}
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bool RefCountedBase::ReleaseRef() const {
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// We don't follow the boost::intrusive_ptr/fit::RefPtr approach here with a
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// release fetch_sub and acquire fence afterwards due to TSAN not supporting
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// fences (see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97868).
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//
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// This approach is a bit less performant - it does the acquiring on each
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// release, not only for the last ref - but otherwise works the same.
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const auto refs = ref_count_.fetch_sub(1, std::memory_order_acq_rel);
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// This assertion will fire if someone manually calls ReleaseRef()
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// on a ref-counted object too many times, or if ReleaseRef is called
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// before an object has been wrapped with RefPtr.
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PW_DCHECK(refs >= 1);
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return refs == 1;
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}
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} // namespace pw::internal
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