| // Copyright 2017 The Dawn & Tint Authors |
| // |
| // Redistribution and use in source and binary forms, with or without |
| // modification, are permitted provided that the following conditions are met: |
| // |
| // 1. Redistributions of source code must retain the above copyright notice, this |
| // list of conditions and the following disclaimer. |
| // |
| // 2. Redistributions in binary form must reproduce the above copyright notice, |
| // this list of conditions and the following disclaimer in the documentation |
| // and/or other materials provided with the distribution. |
| // |
| // 3. Neither the name of the copyright holder nor the names of its |
| // contributors may be used to endorse or promote products derived from |
| // this software without specific prior written permission. |
| // |
| // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" |
| // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE |
| // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE |
| // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL |
| // DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR |
| // SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER |
| // CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, |
| // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| |
| #include "dawn/common/RefCounted.h" |
| |
| #include <cstddef> |
| #if defined(__has_feature) |
| #if __has_feature(thread_sanitizer) |
| #include <sanitizer/tsan_interface.h> |
| #endif |
| #endif |
| |
| #include "dawn/common/Assert.h" |
| |
| namespace dawn { |
| |
| static constexpr size_t kPayloadBits = 1; |
| static constexpr uint64_t kPayloadMask = (uint64_t(1) << kPayloadBits) - 1; |
| static constexpr uint64_t kRefCountIncrement = (uint64_t(1) << kPayloadBits); |
| |
| RefCount::RefCount(uint64_t initCount, uint64_t payload) |
| : mRefCount(initCount * kRefCountIncrement + payload) { |
| DAWN_ASSERT((payload & kPayloadMask) == payload); |
| } |
| |
| RefCount::RefCount(uint64_t payload) : RefCount(1, payload) {} |
| |
| uint64_t RefCount::GetValueForTesting() const { |
| return mRefCount >> kPayloadBits; |
| } |
| |
| uint64_t RefCount::GetPayload() const { |
| // We only care about the payload bits of the refcount. These never change after |
| // initialization so we can use the relaxed memory order. The order doesn't guarantee |
| // anything except the atomicity of the load, which is enough since any past values of the |
| // atomic will have the correct payload bits. |
| return kPayloadMask & mRefCount.load(std::memory_order_relaxed); |
| } |
| |
| bool RefCount::Increment() { |
| // The relaxed ordering guarantees only the atomicity of the update, which is enough here |
| // because the reference we are copying from still exists and makes sure other threads |
| // don't delete `this`. |
| // See the explanation in the Boost documentation: |
| // https://www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html |
| uint32_t previousValue = mRefCount.fetch_add(kRefCountIncrement, std::memory_order_relaxed); |
| |
| return (previousValue & ~kPayloadMask) == 0; |
| } |
| |
| bool RefCount::TryIncrement() { |
| uint64_t current = mRefCount.load(std::memory_order_relaxed); |
| bool success = false; |
| do { |
| if ((current & ~kPayloadMask) == 0u) { |
| return false; |
| } |
| // The relaxed ordering guarantees only the atomicity of the update. This is fine because: |
| // - If another thread's decrement happens before this increment, the increment should |
| // fail. |
| // - If another thread's decrement happens after this increment, the decrement shouldn't |
| // delete the object, because the ref count > 0. |
| // See Boost library for reference: |
| // https://github.com/boostorg/smart_ptr/blob/develop/include/boost/smart_ptr/detail/sp_counted_base_std_atomic.hpp#L62 |
| success = mRefCount.compare_exchange_weak(current, current + kRefCountIncrement, |
| std::memory_order_relaxed); |
| } while (!success); |
| return true; |
| } |
| |
| bool RefCount::Decrement() { |
| DAWN_ASSERT((mRefCount & ~kPayloadMask) != 0); |
| |
| // The release fence here is to make sure all accesses to the object on a thread A |
| // happen-before the object is deleted on a thread B. The release memory order ensures that |
| // all accesses on thread A happen-before the refcount is decreased and the atomic variable |
| // makes sure the refcount decrease in A happens-before the refcount decrease in B. Finally |
| // the acquire fence in the destruction case makes sure the refcount decrease in B |
| // happens-before the `delete this`. |
| // |
| // See the explanation in the Boost documentation: |
| // https://www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html |
| uint64_t previousRefCount = mRefCount.fetch_sub(kRefCountIncrement, std::memory_order_release); |
| |
| // Check that the previous reference count was strictly less than 2, ignoring payload bits. |
| if (previousRefCount < 2 * kRefCountIncrement) { |
| // Note that on ARM64 this will generate a `dmb ish` instruction which is a global |
| // memory barrier, when an acquire load on mRefCount (using the `ldar` instruction) |
| // should be enough and could end up being faster. |
| |
| // https://github.com/google/sanitizers/issues/1415 There is false positive bug in TSAN |
| // when using standalone fence. |
| #if defined(__has_feature) |
| #if __has_feature(thread_sanitizer) |
| __tsan_acquire(&mRefCount); |
| #endif |
| #endif |
| std::atomic_thread_fence(std::memory_order_acquire); |
| return true; |
| } |
| return false; |
| } |
| |
| RefCounted::RefCounted(uint64_t payload) : mRefCount(payload) {} |
| RefCounted::~RefCounted() = default; |
| |
| uint64_t RefCounted::GetRefCountForTesting() const { |
| return mRefCount.GetValueForTesting(); |
| } |
| |
| uint64_t RefCounted::GetRefCountPayload() const { |
| return mRefCount.GetPayload(); |
| } |
| |
| void RefCounted::Reference() { |
| bool result = mRefCount.Increment(); |
| // Never increase ref count from 0. |
| DAWN_ASSERT(!result); |
| } |
| |
| void RefCounted::Release() { |
| if (mRefCount.Decrement()) { |
| DeleteThis(); |
| } |
| } |
| |
| void RefCounted::ReleaseAndLockBeforeDestroy() { |
| if (mRefCount.Decrement()) { |
| LockAndDeleteThis(); |
| } |
| } |
| |
| void RefCounted::DeleteThis() { |
| delete this; |
| } |
| |
| void RefCounted::LockAndDeleteThis() { |
| DeleteThis(); |
| } |
| |
| } // namespace dawn |