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