9a50174dbc
SkOncePtr<T[]> is identical to SkOncePtr<T> except we'll default to delete[] for cleanup. CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Debug-ASAN-Trybot BUG=skia: No public API changes. TBR=reed@google.com Review URL: https://codereview.chromium.org/1311893010
108 lines
3.3 KiB
C++
108 lines
3.3 KiB
C++
/*
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* Copyright 2015 Google Inc.
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#ifndef SkOncePtr_DEFINED
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#define SkOncePtr_DEFINED
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#include "SkAtomics.h"
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#include "SkUniquePtr.h"
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template <typename T> class SkBaseOncePtr;
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// Use this to create a global static pointer that's intialized exactly once when you call get().
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#define SK_DECLARE_STATIC_ONCE_PTR(type, name) namespace {} static SkBaseOncePtr<type> name
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// Use this for a local or member pointer that's initialized exactly once when you call get().
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template <typename T, typename Delete = skstd::default_delete<T>>
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class SkOncePtr : SkNoncopyable {
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public:
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SkOncePtr() { sk_bzero(this, sizeof(*this)); }
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~SkOncePtr() {
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if (T* ptr = (T*)*this) {
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Delete()(ptr);
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}
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}
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template <typename F>
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T* get(const F& f) const {
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return fOnce.get(f);
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}
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operator T*() const {
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return (T*)fOnce;
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}
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private:
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SkBaseOncePtr<T> fOnce;
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};
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// If you ask for SkOncePtr<T[]>, we'll clean up with delete[] by default.
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template <typename T>
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class SkOncePtr<T[]> : public SkOncePtr<T, skstd::default_delete<T[]>> {};
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/* TODO(mtklein): in next CL
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typedef SkBaseOncePtr<void> SkOnceFlag;
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#define SK_DECLARE_STATIC_ONCE(name) namespace {} static SkOnceFlag name
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template <typename F>
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inline void SkOnce(SkOnceFlag* once, const F& f) {
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once->get([&]{ f(); return (void*)2; });
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}
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*/
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// Implementation details below here! No peeking!
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template <typename T>
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class SkBaseOncePtr {
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public:
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template <typename F>
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T* get(const F& f) const {
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uintptr_t state = fState.load(sk_memory_order_acquire);
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if (state < 2) {
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if (state == 0) {
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// It looks like no one has tried to create our pointer yet.
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// We try to claim that task by atomically swapping our state from '0' to '1'.
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if (fState.compare_exchange(&state, 1, sk_memory_order_relaxed,
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sk_memory_order_relaxed)) {
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// We've claimed it. Create our pointer and store it into fState.
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state = (uintptr_t)f();
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SkASSERT(state > 1);
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fState.store(state, sk_memory_order_release);
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} else {
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// Someone else claimed it.
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// We fall through to the spin loop just below to wait for them to finish.
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}
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}
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while (state == 1) {
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// State '1' is our busy-but-not-done state.
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// Some other thread has claimed the job of creating our pointer.
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// We just need to wait for it to finish.
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state = fState.load(sk_memory_order_acquire);
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}
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// We shouldn't be able to get here without having created our pointer.
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SkASSERT(state > 1);
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}
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return (T*)state;
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}
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operator T*() const {
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auto state = fState.load(sk_memory_order_acquire);
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return state < 2 ? nullptr : (T*)state;
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// TODO: If state == 1 spin until it's not?
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}
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private:
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// fState == 0 --> we have not created our ptr yet
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// fState == 1 --> someone is in the middle of creating our ptr
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// else --> (T*)fState is our ptr
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mutable SkAtomic<uintptr_t> fState;
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};
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#endif//SkOncePtr_DEFINED
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