1 /* 2 * Copyright (C) 2018 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef ART_RUNTIME_INTERPRETER_INTERPRETER_CACHE_H_ 18 #define ART_RUNTIME_INTERPRETER_INTERPRETER_CACHE_H_ 19 20 #include <array> 21 #include <atomic> 22 23 #include "base/bit_utils.h" 24 #include "base/macros.h" 25 26 namespace art { 27 28 class Thread; 29 30 // Small fast thread-local cache for the interpreter. 31 // It can hold arbitrary pointer-sized key-value pair. 32 // The interpretation of the value depends on the key. 33 // Presence of entry might imply some pre-conditions. 34 // All operations must be done from the owning thread, 35 // or at a point when the owning thread is suspended. 36 // 37 // The key-value pairs stored in the cache currently are: 38 // iget/iput: The field offset. The field must be non-volatile. 39 // sget/sput: The ArtField* pointer. The field must be non-volitile. 40 // invoke: The ArtMethod* pointer (before vtable indirection, etc). 41 // 42 // We ensure consistency of the cache by clearing it 43 // whenever any dex file is unloaded. 44 // 45 // Aligned to 16-bytes to make it easier to get the address of the cache 46 // from assembly (it ensures that the offset is valid immediate value). 47 class ALIGNED(16) InterpreterCache { 48 // Aligned since we load the whole entry in single assembly instruction. 49 typedef std::pair<const void*, size_t> Entry ALIGNED(2 * sizeof(size_t)); 50 51 public: 52 // 2x size increase/decrease corresponds to ~0.5% interpreter performance change. 53 // Value of 256 has around 75% cache hit rate. 54 static constexpr size_t kSize = 256; 55 InterpreterCache()56 InterpreterCache() { 57 // We can not use the Clear() method since the constructor will not 58 // be called from the owning thread. 59 data_.fill(Entry{}); 60 } 61 62 // Clear the whole cache. It requires the owning thread for DCHECKs. 63 void Clear(Thread* owning_thread); 64 Get(const void * key,size_t * value)65 ALWAYS_INLINE bool Get(const void* key, /* out */ size_t* value) { 66 DCHECK(IsCalledFromOwningThread()); 67 Entry& entry = data_[IndexOf(key)]; 68 if (LIKELY(entry.first == key)) { 69 *value = entry.second; 70 return true; 71 } 72 return false; 73 } 74 Set(const void * key,size_t value)75 ALWAYS_INLINE void Set(const void* key, size_t value) { 76 DCHECK(IsCalledFromOwningThread()); 77 data_[IndexOf(key)] = Entry{key, value}; 78 } 79 80 private: 81 bool IsCalledFromOwningThread(); 82 IndexOf(const void * key)83 static ALWAYS_INLINE size_t IndexOf(const void* key) { 84 static_assert(IsPowerOfTwo(kSize), "Size must be power of two"); 85 size_t index = (reinterpret_cast<uintptr_t>(key) >> 2) & (kSize - 1); 86 DCHECK_LT(index, kSize); 87 return index; 88 } 89 90 std::array<Entry, kSize> data_; 91 }; 92 93 } // namespace art 94 95 #endif // ART_RUNTIME_INTERPRETER_INTERPRETER_CACHE_H_ 96