intern_table.cc revision 94f7b49578b6aaa80de8ffed230648d601393905 
1/*
2 * Copyright (C) 2011 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#include "intern_table.h"
18
19#include <memory>
20
21#include "gc/space/image_space.h"
22#include "mirror/dex_cache.h"
23#include "mirror/object_array-inl.h"
24#include "mirror/object-inl.h"
25#include "mirror/string.h"
26#include "thread.h"
27#include "utf.h"
28
29namespace art {
30
31InternTable::InternTable()
32    : log_new_roots_(false), allow_new_interns_(true),
33      new_intern_condition_("New intern condition", *Locks::intern_table_lock_) {
34}
35
36size_t InternTable::Size() const {
37  MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
38  return strong_interns_.size() + weak_interns_.size();
39}
40
41size_t InternTable::StrongSize() const {
42  MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
43  return strong_interns_.size();
44}
45
46size_t InternTable::WeakSize() const {
47  MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
48  return weak_interns_.size();
49}
50
51void InternTable::DumpForSigQuit(std::ostream& os) const {
52  MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
53  os << "Intern table: " << strong_interns_.size() << " strong; "
54     << weak_interns_.size() << " weak\n";
55}
56
57void InternTable::VisitRoots(RootCallback* callback, void* arg, VisitRootFlags flags) {
58  MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
59  if ((flags & kVisitRootFlagAllRoots) != 0) {
60    for (auto& strong_intern : strong_interns_) {
61      strong_intern.second.VisitRoot(callback, arg, 0, kRootInternedString);
62      DCHECK(!strong_intern.second.IsNull());
63    }
64  } else if ((flags & kVisitRootFlagNewRoots) != 0) {
65    for (auto& pair : new_strong_intern_roots_) {
66      mirror::String* old_ref = pair.second.Read<kWithoutReadBarrier>();
67      pair.second.VisitRoot(callback, arg, 0, kRootInternedString);
68      mirror::String* new_ref = pair.second.Read<kWithoutReadBarrier>();
69      if (UNLIKELY(new_ref != old_ref)) {
70        // Uh ohes, GC moved a root in the log. Need to search the strong interns and update the
71        // corresponding object. This is slow, but luckily for us, this may only happen with a
72        // concurrent moving GC.
73        for (auto it = strong_interns_.lower_bound(pair.first), end = strong_interns_.end();
74             it != end && it->first == pair.first; ++it) {
75          // If the class stored matches the old class, update it to the new value.
76          if (old_ref == it->second.Read<kWithoutReadBarrier>()) {
77            it->second = GcRoot<mirror::String>(new_ref);
78          }
79        }
80      }
81    }
82  }
83
84  if ((flags & kVisitRootFlagClearRootLog) != 0) {
85    new_strong_intern_roots_.clear();
86  }
87  if ((flags & kVisitRootFlagStartLoggingNewRoots) != 0) {
88    log_new_roots_ = true;
89  } else if ((flags & kVisitRootFlagStopLoggingNewRoots) != 0) {
90    log_new_roots_ = false;
91  }
92  // Note: we deliberately don't visit the weak_interns_ table and the immutable image roots.
93}
94
95mirror::String* InternTable::LookupStrong(mirror::String* s, int32_t hash_code) {
96  return Lookup(&strong_interns_, s, hash_code);
97}
98
99mirror::String* InternTable::LookupWeak(mirror::String* s, int32_t hash_code) {
100  // Weak interns need a read barrier because they are weak roots.
101  return Lookup(&weak_interns_, s, hash_code);
102}
103
104mirror::String* InternTable::Lookup(Table* table, mirror::String* s, int32_t hash_code) {
105  Locks::intern_table_lock_->AssertHeld(Thread::Current());
106  for (auto it = table->lower_bound(hash_code), end = table->end();
107       it != end && it->first == hash_code; ++it) {
108    mirror::String* existing_string = it->second.Read();
109    if (existing_string->Equals(s)) {
110      return existing_string;
111    }
112  }
113  return NULL;
114}
115
116mirror::String* InternTable::InsertStrong(mirror::String* s, int32_t hash_code) {
117  Runtime* runtime = Runtime::Current();
118  if (runtime->IsActiveTransaction()) {
119    runtime->RecordStrongStringInsertion(s, hash_code);
120  }
121  if (log_new_roots_) {
122    new_strong_intern_roots_.push_back(std::make_pair(hash_code, GcRoot<mirror::String>(s)));
123  }
124  strong_interns_.insert(std::make_pair(hash_code, GcRoot<mirror::String>(s)));
125  return s;
126}
127
128mirror::String* InternTable::InsertWeak(mirror::String* s, int32_t hash_code) {
129  Runtime* runtime = Runtime::Current();
130  if (runtime->IsActiveTransaction()) {
131    runtime->RecordWeakStringInsertion(s, hash_code);
132  }
133  weak_interns_.insert(std::make_pair(hash_code, GcRoot<mirror::String>(s)));
134  return s;
135}
136
137void InternTable::RemoveStrong(mirror::String* s, int32_t hash_code) {
138  Remove(&strong_interns_, s, hash_code);
139}
140
141void InternTable::RemoveWeak(mirror::String* s, int32_t hash_code) {
142  Runtime* runtime = Runtime::Current();
143  if (runtime->IsActiveTransaction()) {
144    runtime->RecordWeakStringRemoval(s, hash_code);
145  }
146  Remove(&weak_interns_, s, hash_code);
147}
148
149void InternTable::Remove(Table* table, mirror::String* s, int32_t hash_code) {
150  for (auto it = table->lower_bound(hash_code), end = table->end();
151       it != end && it->first == hash_code; ++it) {
152    mirror::String* existing_string = it->second.Read();
153    if (existing_string == s) {
154      table->erase(it);
155      return;
156    }
157  }
158}
159
160// Insert/remove methods used to undo changes made during an aborted transaction.
161mirror::String* InternTable::InsertStrongFromTransaction(mirror::String* s, int32_t hash_code) {
162  DCHECK(!Runtime::Current()->IsActiveTransaction());
163  return InsertStrong(s, hash_code);
164}
165mirror::String* InternTable::InsertWeakFromTransaction(mirror::String* s, int32_t hash_code) {
166  DCHECK(!Runtime::Current()->IsActiveTransaction());
167  return InsertWeak(s, hash_code);
168}
169void InternTable::RemoveStrongFromTransaction(mirror::String* s, int32_t hash_code) {
170  DCHECK(!Runtime::Current()->IsActiveTransaction());
171  RemoveStrong(s, hash_code);
172}
173void InternTable::RemoveWeakFromTransaction(mirror::String* s, int32_t hash_code) {
174  DCHECK(!Runtime::Current()->IsActiveTransaction());
175  RemoveWeak(s, hash_code);
176}
177
178static mirror::String* LookupStringFromImage(mirror::String* s)
179    SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
180  gc::space::ImageSpace* image = Runtime::Current()->GetHeap()->GetImageSpace();
181  if (image == NULL) {
182    return NULL;  // No image present.
183  }
184  mirror::Object* root = image->GetImageHeader().GetImageRoot(ImageHeader::kDexCaches);
185  mirror::ObjectArray<mirror::DexCache>* dex_caches = root->AsObjectArray<mirror::DexCache>();
186  const std::string utf8 = s->ToModifiedUtf8();
187  for (int32_t i = 0; i < dex_caches->GetLength(); ++i) {
188    mirror::DexCache* dex_cache = dex_caches->Get(i);
189    const DexFile* dex_file = dex_cache->GetDexFile();
190    // Binary search the dex file for the string index.
191    const DexFile::StringId* string_id = dex_file->FindStringId(utf8.c_str());
192    if (string_id != NULL) {
193      uint32_t string_idx = dex_file->GetIndexForStringId(*string_id);
194      mirror::String* image = dex_cache->GetResolvedString(string_idx);
195      if (image != NULL) {
196        return image;
197      }
198    }
199  }
200  return NULL;
201}
202
203void InternTable::AllowNewInterns() {
204  Thread* self = Thread::Current();
205  MutexLock mu(self, *Locks::intern_table_lock_);
206  allow_new_interns_ = true;
207  new_intern_condition_.Broadcast(self);
208}
209
210void InternTable::DisallowNewInterns() {
211  Thread* self = Thread::Current();
212  MutexLock mu(self, *Locks::intern_table_lock_);
213  allow_new_interns_ = false;
214}
215
216mirror::String* InternTable::Insert(mirror::String* s, bool is_strong) {
217  Thread* self = Thread::Current();
218  MutexLock mu(self, *Locks::intern_table_lock_);
219
220  DCHECK(s != NULL);
221  uint32_t hash_code = s->GetHashCode();
222
223  while (UNLIKELY(!allow_new_interns_)) {
224    new_intern_condition_.WaitHoldingLocks(self);
225  }
226
227  if (is_strong) {
228    // Check the strong table for a match.
229    mirror::String* strong = LookupStrong(s, hash_code);
230    if (strong != NULL) {
231      return strong;
232    }
233
234    // Check the image for a match.
235    mirror::String* image = LookupStringFromImage(s);
236    if (image != NULL) {
237      return InsertStrong(image, hash_code);
238    }
239
240    // There is no match in the strong table, check the weak table.
241    mirror::String* weak = LookupWeak(s, hash_code);
242    if (weak != NULL) {
243      // A match was found in the weak table. Promote to the strong table.
244      RemoveWeak(weak, hash_code);
245      return InsertStrong(weak, hash_code);
246    }
247
248    // No match in the strong table or the weak table. Insert into the strong
249    // table.
250    return InsertStrong(s, hash_code);
251  }
252
253  // Check the strong table for a match.
254  mirror::String* strong = LookupStrong(s, hash_code);
255  if (strong != NULL) {
256    return strong;
257  }
258  // Check the image for a match.
259  mirror::String* image = LookupStringFromImage(s);
260  if (image != NULL) {
261    return InsertWeak(image, hash_code);
262  }
263  // Check the weak table for a match.
264  mirror::String* weak = LookupWeak(s, hash_code);
265  if (weak != NULL) {
266    return weak;
267  }
268  // Insert into the weak table.
269  return InsertWeak(s, hash_code);
270}
271
272mirror::String* InternTable::InternStrong(int32_t utf16_length, const char* utf8_data) {
273  DCHECK(utf8_data != nullptr);
274  return InternStrong(mirror::String::AllocFromModifiedUtf8(
275      Thread::Current(), utf16_length, utf8_data));
276}
277
278mirror::String* InternTable::InternStrong(const char* utf8_data) {
279  DCHECK(utf8_data != nullptr);
280  return InternStrong(mirror::String::AllocFromModifiedUtf8(Thread::Current(), utf8_data));
281}
282
283mirror::String* InternTable::InternStrong(mirror::String* s) {
284  if (s == nullptr) {
285    return nullptr;
286  }
287  return Insert(s, true);
288}
289
290mirror::String* InternTable::InternWeak(mirror::String* s) {
291  if (s == nullptr) {
292    return nullptr;
293  }
294  return Insert(s, false);
295}
296
297bool InternTable::ContainsWeak(mirror::String* s) {
298  MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
299  const mirror::String* found = LookupWeak(s, s->GetHashCode());
300  return found == s;
301}
302
303void InternTable::SweepInternTableWeaks(IsMarkedCallback* callback, void* arg) {
304  MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
305  for (auto it = weak_interns_.begin(), end = weak_interns_.end(); it != end;) {
306    // This does not need a read barrier because this is called by GC.
307    mirror::Object* object = it->second.Read<kWithoutReadBarrier>();
308    mirror::Object* new_object = callback(object, arg);
309    if (new_object == nullptr) {
310      // TODO: use it = weak_interns_.erase(it) when we get a c++11 stl.
311      weak_interns_.erase(it++);
312    } else {
313      it->second = GcRoot<mirror::String>(down_cast<mirror::String*>(new_object));
314      ++it;
315    }
316  }
317}
318
319}  // namespace art
320