/*
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* Copyright (C) 2018 The Android Open Source Project
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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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*/
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#ifndef ART_RUNTIME_INTERPRETER_INTERPRETER_CACHE_H_
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#define ART_RUNTIME_INTERPRETER_INTERPRETER_CACHE_H_
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#include <array>
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#include <atomic>
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#include "base/bit_utils.h"
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#include "base/macros.h"
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namespace art {
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class Thread;
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// Small fast thread-local cache for the interpreter.
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// It can hold arbitrary pointer-sized key-value pair.
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// The interpretation of the value depends on the key.
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// Presence of entry might imply some pre-conditions.
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// All operations must be done from the owning thread,
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// or at a point when the owning thread is suspended.
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//
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// The key-value pairs stored in the cache currently are:
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// iget/iput: The field offset. The field must be non-volatile.
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// sget/sput: The ArtField* pointer. The field must be non-volitile.
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// invoke: The ArtMethod* pointer (before vtable indirection, etc).
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//
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// We ensure consistency of the cache by clearing it
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// whenever any dex file is unloaded.
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//
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// Aligned to 16-bytes to make it easier to get the address of the cache
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// from assembly (it ensures that the offset is valid immediate value).
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class ALIGNED(16) InterpreterCache {
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// Aligned since we load the whole entry in single assembly instruction.
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typedef std::pair<const void*, size_t> Entry ALIGNED(2 * sizeof(size_t));
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public:
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// 2x size increase/decrease corresponds to ~0.5% interpreter performance change.
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// Value of 256 has around 75% cache hit rate.
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static constexpr size_t kSize = 256;
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InterpreterCache() {
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// We can not use the Clear() method since the constructor will not
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// be called from the owning thread.
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data_.fill(Entry{});
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}
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// Clear the whole cache. It requires the owning thread for DCHECKs.
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void Clear(Thread* owning_thread);
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ALWAYS_INLINE bool Get(const void* key, /* out */ size_t* value) {
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DCHECK(IsCalledFromOwningThread());
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Entry& entry = data_[IndexOf(key)];
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if (LIKELY(entry.first == key)) {
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*value = entry.second;
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return true;
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}
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return false;
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}
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ALWAYS_INLINE void Set(const void* key, size_t value) {
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DCHECK(IsCalledFromOwningThread());
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data_[IndexOf(key)] = Entry{key, value};
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}
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private:
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bool IsCalledFromOwningThread();
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static ALWAYS_INLINE size_t IndexOf(const void* key) {
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static_assert(IsPowerOfTwo(kSize), "Size must be power of two");
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size_t index = (reinterpret_cast<uintptr_t>(key) >> 2) & (kSize - 1);
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DCHECK_LT(index, kSize);
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return index;
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}
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std::array<Entry, kSize> data_;
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};
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} // namespace art
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#endif // ART_RUNTIME_INTERPRETER_INTERPRETER_CACHE_H_
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