1 // Copyright 2011 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
5 #ifndef V8_GLOBAL_HANDLES_H_
6 #define V8_GLOBAL_HANDLES_H_
8 #include "include/v8.h"
9 #include "include/v8-profiler.h"
11 #include "src/handles.h"
13 #include "src/utils.h"
21 // Structure for tracking global handles.
22 // A single list keeps all the allocated global handles.
23 // Destroyed handles stay in the list but is added to the free list.
24 // At GC the destroyed global handles are removed from the free list
27 // Data structures for tracking object groups and implicit references.
29 // An object group is treated like a single JS object: if one of object in
30 // the group is alive, all objects in the same group are considered alive.
31 // An object group is used to simulate object relationship in a DOM tree.
33 // An implicit references group consists of two parts: a parent object and a
34 // list of children objects. If the parent is alive, all the children are alive
38 explicit ObjectGroup(size_t length)
39 : info(NULL), length(length) {
41 objects = new Object**[length];
45 v8::RetainedObjectInfo* info;
51 struct ImplicitRefGroup {
52 ImplicitRefGroup(HeapObject** parent, size_t length)
53 : parent(parent), length(length) {
55 children = new Object**[length];
65 // For internal bookkeeping.
66 struct ObjectGroupConnection {
67 ObjectGroupConnection(UniqueId id, Object** object)
68 : id(id), object(object) {}
70 bool operator==(const ObjectGroupConnection& other) const {
71 return id == other.id;
74 bool operator<(const ObjectGroupConnection& other) const {
83 struct ObjectGroupRetainerInfo {
84 ObjectGroupRetainerInfo(UniqueId id, RetainedObjectInfo* info)
85 : id(id), info(info) {}
87 bool operator==(const ObjectGroupRetainerInfo& other) const {
88 return id == other.id;
91 bool operator<(const ObjectGroupRetainerInfo& other) const {
96 RetainedObjectInfo* info;
101 NORMAL_WEAK, // Embedder gets a handle to the dying object.
102 // In the following cases, the embedder gets the parameter they passed in
103 // earlier, and the 0, 1 or 2 first internal fields. Note that the internal
104 // fields must contain aligned non-V8 pointers. Getting pointers to V8
105 // objects through this interface would be GC unsafe so in that case the
106 // embedder gets a null pointer instead.
107 PHANTOM_WEAK_0_INTERNAL_FIELDS,
108 PHANTOM_WEAK_1_INTERNAL_FIELDS,
109 PHANTOM_WEAK_2_INTERNAL_FIELDS
113 class GlobalHandles {
117 // Creates a new global handle that is alive until Destroy is called.
118 Handle<Object> Create(Object* value);
120 // Copy a global handle
121 static Handle<Object> CopyGlobal(Object** location);
123 // Destroy a global handle.
124 static void Destroy(Object** location);
126 typedef WeakCallbackData<v8::Value, void>::Callback WeakCallback;
128 // For a phantom weak reference, the callback does not have access to the
129 // dying object. Phantom weak references are preferred because they allow
130 // memory to be reclaimed in one GC cycle rather than two. However, for
131 // historical reasons the default is non-phantom.
132 enum PhantomState { Nonphantom, Phantom };
134 // Make the global handle weak and set the callback parameter for the
135 // handle. When the garbage collector recognizes that only weak global
136 // handles point to an object the callback function is invoked (for each
137 // handle) with the handle and corresponding parameter as arguments. By
138 // default the handle still contains a pointer to the object that is being
139 // collected. For this reason the object is not collected until the next
140 // GC. For a phantom weak handle the handle is cleared (set to a Smi)
141 // before the callback is invoked, but the handle can still be identified
142 // in the callback by using the location() of the handle.
143 static void MakeWeak(Object** location, void* parameter,
144 WeakCallback weak_callback);
146 // It would be nice to template this one, but it's really hard to get
147 // the template instantiator to work right if you do.
148 static void MakePhantom(Object** location, void* parameter,
149 int number_of_internal_fields,
150 PhantomCallbackData<void>::Callback weak_callback);
152 void RecordStats(HeapStats* stats);
154 // Returns the current number of weak handles.
155 int NumberOfWeakHandles();
157 // Returns the current number of weak handles to global objects.
158 // These handles are also included in NumberOfWeakHandles().
159 int NumberOfGlobalObjectWeakHandles();
161 // Returns the current number of handles to global objects.
162 int global_handles_count() const {
163 return number_of_global_handles_;
166 // Collect up data for the weak handle callbacks after GC has completed, but
167 // before memory is reclaimed.
168 void CollectAllPhantomCallbackData();
170 // Collect up data for the weak handle callbacks referenced by young
171 // generation after GC has completed, but before memory is reclaimed.
172 void CollectYoungPhantomCallbackData();
174 // Clear the weakness of a global handle.
175 static void* ClearWeakness(Object** location);
177 // Clear the weakness of a global handle.
178 static void MarkIndependent(Object** location);
180 // Mark the reference to this object externaly unreachable.
181 static void MarkPartiallyDependent(Object** location);
183 static bool IsIndependent(Object** location);
185 // Tells whether global handle is near death.
186 static bool IsNearDeath(Object** location);
188 // Tells whether global handle is weak.
189 static bool IsWeak(Object** location);
191 // Process pending weak handles.
192 // Returns the number of freed nodes.
193 int PostGarbageCollectionProcessing(GarbageCollector collector);
195 // Iterates over all strong handles.
196 void IterateStrongRoots(ObjectVisitor* v);
198 // Iterates over all handles.
199 void IterateAllRoots(ObjectVisitor* v);
201 // Iterates over all handles that have embedder-assigned class ID.
202 void IterateAllRootsWithClassIds(ObjectVisitor* v);
204 // Iterates over all handles in the new space that have embedder-assigned
206 void IterateAllRootsInNewSpaceWithClassIds(ObjectVisitor* v);
208 // Iterates over all weak roots in heap.
209 void IterateWeakRoots(ObjectVisitor* v);
211 // Find all weak handles satisfying the callback predicate, mark
213 void IdentifyWeakHandles(WeakSlotCallback f);
215 // NOTE: Three ...NewSpace... functions below are used during
216 // scavenge collections and iterate over sets of handles that are
217 // guaranteed to contain all handles holding new space objects (but
218 // may also include old space objects).
220 // Iterates over strong and dependent handles. See the node above.
221 void IterateNewSpaceStrongAndDependentRoots(ObjectVisitor* v);
223 // Finds weak independent or partially independent handles satisfying
224 // the callback predicate and marks them as pending. See the note above.
225 void IdentifyNewSpaceWeakIndependentHandles(WeakSlotCallbackWithHeap f);
227 // Iterates over weak independent or partially independent handles.
228 // See the note above.
229 void IterateNewSpaceWeakIndependentRoots(ObjectVisitor* v);
231 // Iterate over objects in object groups that have at least one object
232 // which requires visiting. The callback has to return true if objects
233 // can be skipped and false otherwise.
234 bool IterateObjectGroups(ObjectVisitor* v, WeakSlotCallbackWithHeap can_skip);
236 // Add an object group.
237 // Should be only used in GC callback function before a collection.
238 // All groups are destroyed after a garbage collection.
239 void AddObjectGroup(Object*** handles,
241 v8::RetainedObjectInfo* info);
243 // Associates handle with the object group represented by id.
244 // Should be only used in GC callback function before a collection.
245 // All groups are destroyed after a garbage collection.
246 void SetObjectGroupId(Object** handle, UniqueId id);
248 // Set RetainedObjectInfo for an object group. Should not be called more than
249 // once for a group. Should not be called for a group which contains no
251 void SetRetainedObjectInfo(UniqueId id, RetainedObjectInfo* info);
253 // Adds an implicit reference from a group to an object. Should be only used
254 // in GC callback function before a collection. All implicit references are
255 // destroyed after a mark-compact collection.
256 void SetReferenceFromGroup(UniqueId id, Object** child);
258 // Adds an implicit reference from a parent object to a child object. Should
259 // be only used in GC callback function before a collection. All implicit
260 // references are destroyed after a mark-compact collection.
261 void SetReference(HeapObject** parent, Object** child);
263 List<ObjectGroup*>* object_groups() {
264 ComputeObjectGroupsAndImplicitReferences();
265 return &object_groups_;
268 List<ImplicitRefGroup*>* implicit_ref_groups() {
269 ComputeObjectGroupsAndImplicitReferences();
270 return &implicit_ref_groups_;
273 // Remove bags, this should only happen after GC.
274 void RemoveObjectGroups();
275 void RemoveImplicitRefGroups();
277 // Tear down the global handle structure.
280 Isolate* isolate() { return isolate_; }
288 explicit GlobalHandles(Isolate* isolate);
290 // Migrates data from the internal representation (object_group_connections_,
291 // retainer_infos_ and implicit_ref_connections_) to the public and more
292 // efficient representation (object_groups_ and implicit_ref_groups_).
293 void ComputeObjectGroupsAndImplicitReferences();
295 // v8::internal::List is inefficient even for small number of elements, if we
296 // don't assign any initial capacity.
297 static const int kObjectGroupConnectionsCapacity = 20;
299 // Helpers for PostGarbageCollectionProcessing.
300 int PostScavengeProcessing(int initial_post_gc_processing_count);
301 int PostMarkSweepProcessing(int initial_post_gc_processing_count);
302 int DispatchPendingPhantomCallbacks();
303 void UpdateListOfNewSpaceNodes();
305 // Internal node structures.
309 class PendingPhantomCallback;
313 // Field always containing the number of handles to global objects.
314 int number_of_global_handles_;
316 // List of all allocated node blocks.
317 NodeBlock* first_block_;
319 // List of node blocks with used nodes.
320 NodeBlock* first_used_block_;
322 // Free list of nodes.
325 // Contains all nodes holding new space objects. Note: when the list
326 // is accessed, some of the objects may have been promoted already.
327 List<Node*> new_space_nodes_;
329 int post_gc_processing_count_;
331 // Object groups and implicit references, public and more efficient
333 List<ObjectGroup*> object_groups_;
334 List<ImplicitRefGroup*> implicit_ref_groups_;
336 // Object groups and implicit references, temporary representation while
337 // constructing the groups.
338 List<ObjectGroupConnection> object_group_connections_;
339 List<ObjectGroupRetainerInfo> retainer_infos_;
340 List<ObjectGroupConnection> implicit_ref_connections_;
342 List<PendingPhantomCallback> pending_phantom_callbacks_;
344 friend class Isolate;
346 DISALLOW_COPY_AND_ASSIGN(GlobalHandles);
350 class GlobalHandles::PendingPhantomCallback {
352 typedef PhantomCallbackData<void> Data;
353 PendingPhantomCallback(Node* node, Data data, Data::Callback callback)
354 : node_(node), data_(data), callback_(callback) {}
358 Node* node() { return node_; }
363 Data::Callback callback_;
367 class EternalHandles {
369 enum SingletonHandle {
374 NUMBER_OF_SINGLETON_HANDLES
380 int NumberOfHandles() { return size_; }
382 // Create an EternalHandle, overwriting the index.
383 void Create(Isolate* isolate, Object* object, int* index);
385 // Grab the handle for an existing EternalHandle.
386 inline Handle<Object> Get(int index) {
387 return Handle<Object>(GetLocation(index));
390 // Grab the handle for an existing SingletonHandle.
391 inline Handle<Object> GetSingleton(SingletonHandle singleton) {
392 DCHECK(Exists(singleton));
393 return Get(singleton_handles_[singleton]);
396 // Checks whether a SingletonHandle has been assigned.
397 inline bool Exists(SingletonHandle singleton) {
398 return singleton_handles_[singleton] != kInvalidIndex;
401 // Assign a SingletonHandle to an empty slot and returns the handle.
402 Handle<Object> CreateSingleton(Isolate* isolate,
404 SingletonHandle singleton) {
405 Create(isolate, object, &singleton_handles_[singleton]);
406 return Get(singleton_handles_[singleton]);
409 // Iterates over all handles.
410 void IterateAllRoots(ObjectVisitor* visitor);
411 // Iterates over all handles which might be in new space.
412 void IterateNewSpaceRoots(ObjectVisitor* visitor);
413 // Rebuilds new space list.
414 void PostGarbageCollectionProcessing(Heap* heap);
417 static const int kInvalidIndex = -1;
418 static const int kShift = 8;
419 static const int kSize = 1 << kShift;
420 static const int kMask = 0xff;
422 // Gets the slot for an index
423 inline Object** GetLocation(int index) {
424 DCHECK(index >= 0 && index < size_);
425 return &blocks_[index >> kShift][index & kMask];
429 List<Object**> blocks_;
430 List<int> new_space_indices_;
431 int singleton_handles_[NUMBER_OF_SINGLETON_HANDLES];
433 DISALLOW_COPY_AND_ASSIGN(EternalHandles);
437 } } // namespace v8::internal
439 #endif // V8_GLOBAL_HANDLES_H_