1 /*
2  * Copyright (C) 2015 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_CLASS_TABLE_H_
18 #define ART_RUNTIME_CLASS_TABLE_H_
19 
20 #include <string>
21 #include <utility>
22 #include <vector>
23 
24 #include "base/allocator.h"
25 #include "base/hash_set.h"
26 #include "base/macros.h"
27 #include "base/mutex.h"
28 #include "gc_root.h"
29 #include "obj_ptr.h"
30 
31 namespace art {
32 
33 class OatFile;
34 
35 namespace linker {
36 class ImageWriter;
37 }  // namespace linker
38 
39 namespace linker {
40 class OatWriter;
41 }  // namespace linker
42 
43 namespace mirror {
44 class Class;
45 class ClassLoader;
46 class Object;
47 }  // namespace mirror
48 
49 // Each loader has a ClassTable
50 class ClassTable {
51  public:
52   class TableSlot {
53    public:
TableSlot()54     TableSlot() : data_(0u) {}
55 
TableSlot(const TableSlot & copy)56     TableSlot(const TableSlot& copy) : data_(copy.data_.load(std::memory_order_relaxed)) {}
57 
58     explicit TableSlot(ObjPtr<mirror::Class> klass);
59 
60     TableSlot(ObjPtr<mirror::Class> klass, uint32_t descriptor_hash);
61 
62     TableSlot& operator=(const TableSlot& copy) {
63       data_.store(copy.data_.load(std::memory_order_relaxed), std::memory_order_relaxed);
64       return *this;
65     }
66 
67     bool IsNull() const REQUIRES_SHARED(Locks::mutator_lock_);
68 
Hash()69     uint32_t Hash() const {
70       return MaskHash(data_.load(std::memory_order_relaxed));
71     }
72 
MaskHash(uint32_t hash)73     static uint32_t MaskHash(uint32_t hash) {
74       return hash & kHashMask;
75     }
76 
MaskedHashEquals(uint32_t other)77     bool MaskedHashEquals(uint32_t other) const {
78       return MaskHash(other) == Hash();
79     }
80 
81     static uint32_t HashDescriptor(ObjPtr<mirror::Class> klass)
82         REQUIRES_SHARED(Locks::mutator_lock_);
83 
84     template<ReadBarrierOption kReadBarrierOption = kWithReadBarrier>
85     ObjPtr<mirror::Class> Read() const REQUIRES_SHARED(Locks::mutator_lock_);
86 
87     // NO_THREAD_SAFETY_ANALYSIS since the visitor may require heap bitmap lock.
88     template<typename Visitor>
89     void VisitRoot(const Visitor& visitor) const NO_THREAD_SAFETY_ANALYSIS;
90 
91    private:
92     // Extract a raw pointer from an address.
93     static ObjPtr<mirror::Class> ExtractPtr(uint32_t data)
94         REQUIRES_SHARED(Locks::mutator_lock_);
95 
96     static uint32_t Encode(ObjPtr<mirror::Class> klass, uint32_t hash_bits)
97         REQUIRES_SHARED(Locks::mutator_lock_);
98 
99     // Data contains the class pointer GcRoot as well as the low bits of the descriptor hash.
100     mutable Atomic<uint32_t> data_;
101     static const uint32_t kHashMask = kObjectAlignment - 1;
102   };
103 
104   using DescriptorHashPair = std::pair<const char*, uint32_t>;
105 
106   class ClassDescriptorHashEquals {
107    public:
108     // uint32_t for cross compilation.
109     uint32_t operator()(const TableSlot& slot) const NO_THREAD_SAFETY_ANALYSIS;
110     // Same class loader and descriptor.
111     bool operator()(const TableSlot& a, const TableSlot& b) const
112         NO_THREAD_SAFETY_ANALYSIS;
113     // Same descriptor.
114     bool operator()(const TableSlot& a, const DescriptorHashPair& b) const
115         NO_THREAD_SAFETY_ANALYSIS;
116     // uint32_t for cross compilation.
117     uint32_t operator()(const DescriptorHashPair& pair) const NO_THREAD_SAFETY_ANALYSIS;
118   };
119 
120   class TableSlotEmptyFn {
121    public:
MakeEmpty(TableSlot & item)122     void MakeEmpty(TableSlot& item) const NO_THREAD_SAFETY_ANALYSIS {
123       item = TableSlot();
124       DCHECK(IsEmpty(item));
125     }
IsEmpty(const TableSlot & item)126     bool IsEmpty(const TableSlot& item) const NO_THREAD_SAFETY_ANALYSIS {
127       return item.IsNull();
128     }
129   };
130 
131   // Hash set that hashes class descriptor, and compares descriptors and class loaders. Results
132   // should be compared for a matching class descriptor and class loader.
133   typedef HashSet<TableSlot,
134                   TableSlotEmptyFn,
135                   ClassDescriptorHashEquals,
136                   ClassDescriptorHashEquals,
137                   TrackingAllocator<TableSlot, kAllocatorTagClassTable>> ClassSet;
138 
139   ClassTable();
140 
141   // Used by image writer for checking.
142   bool Contains(ObjPtr<mirror::Class> klass)
143       REQUIRES(!lock_)
144       REQUIRES_SHARED(Locks::mutator_lock_);
145 
146   // Freeze the current class tables by allocating a new table and never updating or modifying the
147   // existing table. This helps prevents dirty pages after caused by inserting after zygote fork.
148   void FreezeSnapshot()
149       REQUIRES(!lock_)
150       REQUIRES_SHARED(Locks::mutator_lock_);
151 
152   // Returns the number of classes in previous snapshots defined by `defining_loader`.
153   size_t NumZygoteClasses(ObjPtr<mirror::ClassLoader> defining_loader) const
154       REQUIRES(!lock_)
155       REQUIRES_SHARED(Locks::mutator_lock_);
156 
157   // Returns all off the classes in the lastest snapshot defined by `defining_loader`.
158   size_t NumNonZygoteClasses(ObjPtr<mirror::ClassLoader> defining_loader) const
159       REQUIRES(!lock_)
160       REQUIRES_SHARED(Locks::mutator_lock_);
161 
162   // Returns the number of classes in previous snapshots no matter the defining loader.
163   size_t NumReferencedZygoteClasses() const
164       REQUIRES(!lock_)
165       REQUIRES_SHARED(Locks::mutator_lock_);
166 
167   // Returns all off the classes in the lastest snapshot no matter the defining loader.
168   size_t NumReferencedNonZygoteClasses() const
169       REQUIRES(!lock_)
170       REQUIRES_SHARED(Locks::mutator_lock_);
171 
172   // Update a class in the table with the new class. Returns the existing class which was replaced.
173   ObjPtr<mirror::Class> UpdateClass(const char* descriptor,
174                                     ObjPtr<mirror::Class> new_klass,
175                                     size_t hash)
176       REQUIRES(!lock_)
177       REQUIRES_SHARED(Locks::mutator_lock_);
178 
179   // NO_THREAD_SAFETY_ANALYSIS for object marking requiring heap bitmap lock.
180   template<class Visitor>
181   void VisitRoots(Visitor& visitor)
182       NO_THREAD_SAFETY_ANALYSIS
183       REQUIRES(!lock_)
184       REQUIRES_SHARED(Locks::mutator_lock_);
185 
186   template<class Visitor>
187   void VisitRoots(const Visitor& visitor)
188       NO_THREAD_SAFETY_ANALYSIS
189       REQUIRES(!lock_)
190       REQUIRES_SHARED(Locks::mutator_lock_);
191 
192   // Stops visit if the visitor returns false.
193   template <typename Visitor, ReadBarrierOption kReadBarrierOption = kWithReadBarrier>
194   bool Visit(Visitor& visitor)
195       REQUIRES(!lock_)
196       REQUIRES_SHARED(Locks::mutator_lock_);
197   template <typename Visitor, ReadBarrierOption kReadBarrierOption = kWithReadBarrier>
198   bool Visit(const Visitor& visitor)
199       REQUIRES(!lock_)
200       REQUIRES_SHARED(Locks::mutator_lock_);
201 
202   // Return the first class that matches the descriptor. Returns null if there are none.
203   ObjPtr<mirror::Class> Lookup(const char* descriptor, size_t hash)
204       REQUIRES(!lock_)
205       REQUIRES_SHARED(Locks::mutator_lock_);
206 
207   // Return the first class that matches the descriptor of klass. Returns null if there are none.
208   ObjPtr<mirror::Class> LookupByDescriptor(ObjPtr<mirror::Class> klass)
209       REQUIRES(!lock_)
210       REQUIRES_SHARED(Locks::mutator_lock_);
211 
212   // Try to insert a class and return the inserted class if successful. If another class
213   // with the same descriptor is already in the table, return the existing entry.
214   ObjPtr<mirror::Class> TryInsert(ObjPtr<mirror::Class> klass)
215       REQUIRES(!lock_)
216       REQUIRES_SHARED(Locks::mutator_lock_);
217 
218   void Insert(ObjPtr<mirror::Class> klass)
219       REQUIRES(!lock_)
220       REQUIRES_SHARED(Locks::mutator_lock_);
221 
222   void InsertWithHash(ObjPtr<mirror::Class> klass, size_t hash)
223       REQUIRES(!lock_)
224       REQUIRES_SHARED(Locks::mutator_lock_);
225 
226   // Returns true if the class was found and removed, false otherwise.
227   bool Remove(const char* descriptor)
228       REQUIRES(!lock_)
229       REQUIRES_SHARED(Locks::mutator_lock_);
230 
231   // Return true if we inserted the strong root, false if it already exists.
232   bool InsertStrongRoot(ObjPtr<mirror::Object> obj)
233       REQUIRES(!lock_)
234       REQUIRES_SHARED(Locks::mutator_lock_);
235 
236   // Return true if we inserted the oat file, false if it already exists.
237   bool InsertOatFile(const OatFile* oat_file)
238       REQUIRES(!lock_)
239       REQUIRES_SHARED(Locks::mutator_lock_);
240 
241   // Combines all of the tables into one class set.
242   size_t WriteToMemory(uint8_t* ptr) const
243       REQUIRES(!lock_)
244       REQUIRES_SHARED(Locks::mutator_lock_);
245 
246   // Read a table from ptr and put it at the front of the class set.
247   size_t ReadFromMemory(uint8_t* ptr)
248       REQUIRES(!lock_)
249       REQUIRES_SHARED(Locks::mutator_lock_);
250 
251   // Add a class set to the front of classes.
252   void AddClassSet(ClassSet&& set)
253       REQUIRES(!lock_)
254       REQUIRES_SHARED(Locks::mutator_lock_);
255 
256   // Clear strong roots (other than classes themselves).
257   void ClearStrongRoots()
258       REQUIRES(!lock_)
259       REQUIRES_SHARED(Locks::mutator_lock_);
260 
261   // Filter strong roots (other than classes themselves).
262   template <typename Filter>
263   void RemoveStrongRoots(const Filter& filter)
264       REQUIRES(!lock_)
265       REQUIRES_SHARED(Locks::mutator_lock_);
266 
GetLock()267   ReaderWriterMutex& GetLock() {
268     return lock_;
269   }
270 
271  private:
272   // Only copies classes.
273   void CopyWithoutLocks(const ClassTable& source_table) NO_THREAD_SAFETY_ANALYSIS;
274   void InsertWithoutLocks(ObjPtr<mirror::Class> klass) NO_THREAD_SAFETY_ANALYSIS;
275 
276   size_t CountDefiningLoaderClasses(ObjPtr<mirror::ClassLoader> defining_loader,
277                                     const ClassSet& set) const
278       REQUIRES(lock_)
279       REQUIRES_SHARED(Locks::mutator_lock_);
280 
281   // Return true if we inserted the oat file, false if it already exists.
282   bool InsertOatFileLocked(const OatFile* oat_file)
283       REQUIRES(lock_)
284       REQUIRES_SHARED(Locks::mutator_lock_);
285 
286   // Lock to guard inserting and removing.
287   mutable ReaderWriterMutex lock_;
288   // We have a vector to help prevent dirty pages after the zygote forks by calling FreezeSnapshot.
289   std::vector<ClassSet> classes_ GUARDED_BY(lock_);
290   // Extra strong roots that can be either dex files or dex caches. Dex files used by the class
291   // loader which may not be owned by the class loader must be held strongly live. Also dex caches
292   // are held live to prevent them being unloading once they have classes in them.
293   std::vector<GcRoot<mirror::Object>> strong_roots_ GUARDED_BY(lock_);
294   // Keep track of oat files with GC roots associated with dex caches in `strong_roots_`.
295   std::vector<const OatFile*> oat_files_ GUARDED_BY(lock_);
296 
297   friend class linker::ImageWriter;  // for InsertWithoutLocks.
298 };
299 
300 }  // namespace art
301 
302 #endif  // ART_RUNTIME_CLASS_TABLE_H_
303