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2ce4b905b2
This means that calling wgpu::Object::DoStuff will translate to a call to dawn_native::ObjectBase::APIDoStuff. This will clarify the difference between reentrant calls and internal calls in dawn_native. Avoiding issues in the future. This CL only changes the code generator to prefix with "API", performs renames needed to make the code compile, and adds TODOs for things that should be fixed in follow-up CLs. Bug: dawn:723 Change-Id: Ie24471fa093adc4179d33d13323429847d076ecb Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/45921 Commit-Queue: Corentin Wallez <cwallez@chromium.org> Auto-Submit: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Austin Eng <enga@chromium.org> Reviewed-by: Stephen White <senorblanco@chromium.org>
87 lines
3.4 KiB
C++
87 lines
3.4 KiB
C++
// Copyright 2017 The Dawn Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://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,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "common/RefCounted.h"
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#include "common/Assert.h"
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#include <cstddef>
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static constexpr size_t kPayloadBits = 1;
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static constexpr uint64_t kPayloadMask = (uint64_t(1) << kPayloadBits) - 1;
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static constexpr uint64_t kRefCountIncrement = (uint64_t(1) << kPayloadBits);
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RefCounted::RefCounted(uint64_t payload) : mRefCount(kRefCountIncrement + payload) {
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ASSERT((payload & kPayloadMask) == payload);
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}
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uint64_t RefCounted::GetRefCountForTesting() const {
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return mRefCount >> kPayloadBits;
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}
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uint64_t RefCounted::GetRefCountPayload() const {
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// We only care about the payload bits of the refcount. These never change after
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// initialization so we can use the relaxed memory order. The order doesn't guarantee
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// anything except the atomicity of the load, which is enough since any past values of the
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// atomic will have the correct payload bits.
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return kPayloadMask & mRefCount.load(std::memory_order_relaxed);
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}
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void RefCounted::Reference() {
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ASSERT((mRefCount & ~kPayloadMask) != 0);
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// The relaxed ordering guarantees only the atomicity of the update, which is enough here
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// because the reference we are copying from still exists and makes sure other threads
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// don't delete `this`.
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// See the explanation in the Boost documentation:
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// https://www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html
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mRefCount.fetch_add(kRefCountIncrement, std::memory_order_relaxed);
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}
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void RefCounted::Release() {
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ASSERT((mRefCount & ~kPayloadMask) != 0);
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// The release fence here is to make sure all accesses to the object on a thread A
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// happen-before the object is deleted on a thread B. The release memory order ensures that
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// all accesses on thread A happen-before the refcount is decreased and the atomic variable
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// makes sure the refcount decrease in A happens-before the refcount decrease in B. Finally
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// the acquire fence in the destruction case makes sure the refcount decrease in B
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// happens-before the `delete this`.
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//
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// See the explanation in the Boost documentation:
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// https://www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html
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uint64_t previousRefCount = mRefCount.fetch_sub(kRefCountIncrement, std::memory_order_release);
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// Check that the previous reference count was strictly less than 2, ignoring payload bits.
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if (previousRefCount < 2 * kRefCountIncrement) {
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// Note that on ARM64 this will generate a `dmb ish` instruction which is a global
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// memory barrier, when an acquire load on mRefCount (using the `ldar` instruction)
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// should be enough and could end up being faster.
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std::atomic_thread_fence(std::memory_order_acquire);
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DeleteThis();
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}
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}
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void RefCounted::APIReference() {
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Reference();
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}
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void RefCounted::APIRelease() {
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Release();
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}
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void RefCounted::DeleteThis() {
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delete this;
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}
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