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/*
* Copyright (C) 2018 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef ART_RUNTIME_INTERPRETER_INTERPRETER_CACHE_H_
#define ART_RUNTIME_INTERPRETER_INTERPRETER_CACHE_H_
#include <array>
#include <atomic>
#include "base/bit_utils.h"
#include "base/macros.h"
namespace art {
class Thread;
// Small fast thread-local cache for the interpreter.
// It can hold arbitrary pointer-sized key-value pair.
// The interpretation of the value depends on the key.
// Presence of entry might imply some pre-conditions.
// All operations must be done from the owning thread,
// or at a point when the owning thread is suspended.
//
// The key-value pairs stored in the cache currently are:
// iget/iput: The field offset. The field must be non-volatile.
// sget/sput: The ArtField* pointer. The field must be non-volitile.
// invoke: The ArtMethod* pointer (before vtable indirection, etc).
//
// We ensure consistency of the cache by clearing it
// whenever any dex file is unloaded.
//
// Aligned to 16-bytes to make it easier to get the address of the cache
// from assembly (it ensures that the offset is valid immediate value).
class ALIGNED(16) InterpreterCache {
public:
// Aligned since we load the whole entry in single assembly instruction.
typedef std::pair<const void*, size_t> Entry ALIGNED(2 * sizeof(size_t));
// 2x size increase/decrease corresponds to ~0.5% interpreter performance change.
// Value of 256 has around 75% cache hit rate.
static constexpr size_t kSize = 256;
InterpreterCache() {
// We can not use the Clear() method since the constructor will not
// be called from the owning thread.
data_.fill(Entry{});
}
// Clear the whole cache. It requires the owning thread for DCHECKs.
void Clear(Thread* owning_thread);
ALWAYS_INLINE bool Get(const void* key, /* out */ size_t* value) {
DCHECK(IsCalledFromOwningThread());
Entry& entry = data_[IndexOf(key)];
if (LIKELY(entry.first == key)) {
*value = entry.second;
return true;
}
return false;
}
ALWAYS_INLINE void Set(const void* key, size_t value) {
DCHECK(IsCalledFromOwningThread());
data_[IndexOf(key)] = Entry{key, value};
}
std::array<Entry, kSize>& GetArray() {
return data_;
}
private:
bool IsCalledFromOwningThread();
static ALWAYS_INLINE size_t IndexOf(const void* key) {
static_assert(IsPowerOfTwo(kSize), "Size must be power of two");
size_t index = (reinterpret_cast<uintptr_t>(key) >> 2) & (kSize - 1);
DCHECK_LT(index, kSize);
return index;
}
std::array<Entry, kSize> data_;
};
} // namespace art
#endif // ART_RUNTIME_INTERPRETER_INTERPRETER_CACHE_H_
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