// Copyright 2006-2008 the V8 project authors. All rights reserved. // Redistribution and use in source and binary forms, with or without // modification, are permitted provided that the following conditions are // met: // // * Redistributions of source code must retain the above copyright // notice, this list of conditions and the following disclaimer. // * Redistributions in binary form must reproduce the above // copyright notice, this list of conditions and the following // disclaimer in the documentation and/or other materials provided // with the distribution. // * Neither the name of Google Inc. nor the names of its // contributors may be used to endorse or promote products derived // from this software without specific prior written permission. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. #ifndef V8_MARK_COMPACT_H_ #define V8_MARK_COMPACT_H_ namespace v8 { namespace internal { // Callback function, returns whether an object is alive. The heap size // of the object is returned in size. It optionally updates the offset // to the first live object in the page (only used for old and map objects). typedef bool (*IsAliveFunction)(HeapObject* obj, int* size, int* offset); // Callback function for non-live blocks in the old generation. typedef void (*DeallocateFunction)(Address start, int size_in_bytes); // Forward declarations. class RootMarkingVisitor; class MarkingVisitor; // ---------------------------------------------------------------------------- // Mark-Compact collector // // All methods are static. class MarkCompactCollector : public AllStatic { public: // Type of functions to compute forwarding addresses of objects in // compacted spaces. Given an object and its size, return a (non-failure) // Object* that will be the object after forwarding. There is a separate // allocation function for each (compactable) space based on the location // of the object before compaction. typedef Object* (*AllocationFunction)(HeapObject* object, int object_size); // Type of functions to encode the forwarding address for an object. // Given the object, its size, and the new (non-failure) object it will be // forwarded to, encode the forwarding address. For paged spaces, the // 'offset' input/output parameter contains the offset of the forwarded // object from the forwarding address of the previous live object in the // page as input, and is updated to contain the offset to be used for the // next live object in the same page. For spaces using a different // encoding (ie, contiguous spaces), the offset parameter is ignored. typedef void (*EncodingFunction)(HeapObject* old_object, int object_size, Object* new_object, int* offset); // Type of functions to process non-live objects. typedef void (*ProcessNonLiveFunction)(HeapObject* object); // Performs a global garbage collection. static void CollectGarbage(GCTracer* tracer); // True if the last full GC performed heap compaction. static bool HasCompacted() { return compacting_collection_; } // True after the Prepare phase if the compaction is taking place. static bool IsCompacting() { return compacting_collection_; } // The count of the number of objects left marked at the end of the last // completed full GC (expected to be zero). static int previous_marked_count() { return previous_marked_count_; } // During a full GC, there is a stack-allocated GCTracer that is used for // bookkeeping information. Return a pointer to that tracer. static GCTracer* tracer() { return tracer_; } #ifdef DEBUG // Checks whether performing mark-compact collection. static bool in_use() { return state_ > PREPARE_GC; } #endif private: #ifdef DEBUG enum CollectorState { IDLE, PREPARE_GC, MARK_LIVE_OBJECTS, SWEEP_SPACES, ENCODE_FORWARDING_ADDRESSES, UPDATE_POINTERS, RELOCATE_OBJECTS, REBUILD_RSETS }; // The current stage of the collector. static CollectorState state_; #endif // Global flag indicating whether spaces were compacted on the last GC. static bool compacting_collection_; // The number of objects left marked at the end of the last completed full // GC (expected to be zero). static int previous_marked_count_; // A pointer to the current stack-allocated GC tracer object during a full // collection (NULL before and after). static GCTracer* tracer_; // Prepares for GC by resetting relocation info in old and map spaces and // choosing spaces to compact. static void Prepare(); // Finishes GC, performs heap verification. static void Finish(); // -------------------------------------------------------------------------- // Phase 1: functions related to marking phase. // before: Heap is in normal state, collector is 'IDLE'. // // The first word of a page in old spaces has the end of // allocation address of the page. // // The word at Chunk::high_ address has the address of the // first page in the next chunk. (The address is tagged to // distinguish it from end-of-allocation address). // // after: live objects are marked. friend class RootMarkingVisitor; friend class MarkingVisitor; // Marking operations for objects reachable from roots. static void MarkLiveObjects(); static void MarkUnmarkedObject(HeapObject* obj); static inline void MarkObject(HeapObject* obj) { if (!obj->IsMarked()) MarkUnmarkedObject(obj); } static inline void SetMark(HeapObject* obj) { tracer_->increment_marked_count(); #ifdef DEBUG UpdateLiveObjectCount(obj); #endif obj->SetMark(); } // Creates back pointers for all map transitions, stores them in // the prototype field. The original prototype pointers are restored // in ClearNonLiveTransitions(). All JSObject maps // connected by map transitions have the same prototype object, which // is why we can use this field temporarily for back pointers. static void CreateBackPointers(); // Mark a Map and its DescriptorArray together, skipping transitions. static void MarkMapContents(Map* map); static void MarkDescriptorArray(DescriptorArray* descriptors); // Mark the heap roots and all objects reachable from them. static void ProcessRoots(RootMarkingVisitor* visitor); // Mark objects in object groups that have at least one object in the // group marked. static void MarkObjectGroups(); // Mark all objects in an object group with at least one marked // object, then all objects reachable from marked objects in object // groups, and repeat. static void ProcessObjectGroups(MarkingVisitor* visitor); // Mark objects reachable (transitively) from objects in the marking stack // or overflowed in the heap. static void ProcessMarkingStack(MarkingVisitor* visitor); // Mark objects reachable (transitively) from objects in the marking // stack. This function empties the marking stack, but may leave // overflowed objects in the heap, in which case the marking stack's // overflow flag will be set. static void EmptyMarkingStack(MarkingVisitor* visitor); // Refill the marking stack with overflowed objects from the heap. This // function either leaves the marking stack full or clears the overflow // flag on the marking stack. static void RefillMarkingStack(); // Callback function for telling whether the object *p must be marked. static bool MustBeMarked(Object** p); #ifdef DEBUG static void UpdateLiveObjectCount(HeapObject* obj); static void VerifyHeapAfterMarkingPhase(); #endif // We sweep the large object space in the same way whether we are // compacting or not, because the large object space is never compacted. static void SweepLargeObjectSpace(); // Test whether a (possibly marked) object is a Map. static inline bool SafeIsMap(HeapObject* object); // Map transitions from a live map to a dead map must be killed. // We replace them with a null descriptor, with the same key. static void ClearNonLiveTransitions(); // -------------------------------------------------------------------------- // Phase 2: functions related to computing and encoding forwarding pointers // before: live objects' map pointers are marked as '00' // after: Map pointers of live old and map objects have encoded // forwarding pointers and map pointers // // The 3rd word of a page has the page top offset after compaction. // // The 4th word of a page in the map space has the map index // of this page in the map table. This word is not used in // the old space. // // The 5th and 6th words of a page have the start and end // addresses of the first free region in the page. // // The 7th word of a page in old spaces has the forwarding address // of the first live object in the page. // // Live young objects have their forwarding pointers in // the from space at the same offset to the beginning of the space. // Encodes forwarding addresses of objects in compactable parts of the // heap. static void EncodeForwardingAddresses(); // Encodes the forwarding addresses of objects in new space. static void EncodeForwardingAddressesInNewSpace(); // Function template to encode the forwarding addresses of objects in // paged spaces, parameterized by allocation and non-live processing // functions. template static void EncodeForwardingAddressesInPagedSpace(PagedSpace* space); // Iterates live objects in a space, passes live objects // to a callback function which returns the heap size of the object. // Returns the number of live objects iterated. static int IterateLiveObjects(NewSpace* space, HeapObjectCallback size_f); static int IterateLiveObjects(PagedSpace* space, HeapObjectCallback size_f); // Iterates the live objects between a range of addresses, returning the // number of live objects. static int IterateLiveObjectsInRange(Address start, Address end, HeapObjectCallback size_func); // Callback functions for deallocating non-live blocks in the old // generation. static void DeallocateOldPointerBlock(Address start, int size_in_bytes); static void DeallocateOldDataBlock(Address start, int size_in_bytes); static void DeallocateCodeBlock(Address start, int size_in_bytes); static void DeallocateMapBlock(Address start, int size_in_bytes); // Phase 2: If we are not compacting the heap, we simply sweep the spaces // except for the large object space, clearing mark bits and adding // unmarked regions to each space's free list. static void SweepSpaces(); #ifdef DEBUG static void VerifyHeapAfterEncodingForwardingAddresses(); #endif // -------------------------------------------------------------------------- // Phase 3: function related to updating pointers and decode map pointers // before: see after phase 2 // after: all pointers are updated to forwarding addresses. friend class UpdatingVisitor; // helper for updating visited objects // Updates pointers in all spaces. static void UpdatePointers(); // Updates pointers in an object in new space. // Returns the heap size of the object. static int UpdatePointersInNewObject(HeapObject* obj); // Updates pointers in an object in old spaces. // Returns the heap size of the object. static int UpdatePointersInOldObject(HeapObject* obj); // Calculates the forwarding address of an object in an old space. static Address GetForwardingAddressInOldSpace(HeapObject* obj); #ifdef DEBUG static void VerifyHeapAfterUpdatingPointers(); #endif // -------------------------------------------------------------------------- // Phase 4: functions related to relocating objects // before: see after phase 3 // after: heap is in a normal state, except remembered set is not built // Relocates objects in all spaces. static void RelocateObjects(); // Converts a code object's inline target to addresses, convention from // address to target happens in the marking phase. static int ConvertCodeICTargetToAddress(HeapObject* obj); // Relocate a map object. static int RelocateMapObject(HeapObject* obj); // Relocates an old object. static int RelocateOldPointerObject(HeapObject* obj); static int RelocateOldDataObject(HeapObject* obj); // Helper function. static inline int RelocateOldNonCodeObject(HeapObject* obj, OldSpace* space); // Relocates an object in the code space. static int RelocateCodeObject(HeapObject* obj); // Copy a new object. static int RelocateNewObject(HeapObject* obj); #ifdef DEBUG static void VerifyHeapAfterRelocatingObjects(); #endif // --------------------------------------------------------------------------- // Phase 5: functions related to rebuilding remembered sets // Rebuild remembered set in old and map spaces. static void RebuildRSets(); #ifdef DEBUG // --------------------------------------------------------------------------- // Debugging variables, functions and classes // Counters used for debugging the marking phase of mark-compact or // mark-sweep collection. // Number of live objects in Heap::to_space_. static int live_young_objects_; // Number of live objects in Heap::old_pointer_space_. static int live_old_pointer_objects_; // Number of live objects in Heap::old_data_space_. static int live_old_data_objects_; // Number of live objects in Heap::code_space_. static int live_code_objects_; // Number of live objects in Heap::map_space_. static int live_map_objects_; // Number of live objects in Heap::lo_space_. static int live_lo_objects_; // Number of live bytes in this collection. static int live_bytes_; static void VerifyPageHeaders(PagedSpace* space); // Verification functions when relocating objects. friend class VerifyCopyingVisitor; static void VerifyCopyingObjects(Object** p); friend class MarkObjectVisitor; static void VisitObject(HeapObject* obj); friend class UnmarkObjectVisitor; static void UnmarkObject(HeapObject* obj); #endif }; } } // namespace v8::internal #endif // V8_MARK_COMPACT_H_