1 // Copyright 2020 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. 4 5 #ifndef V8_HEAP_CPPGC_GC_INFO_TABLE_H_ 6 #define V8_HEAP_CPPGC_GC_INFO_TABLE_H_ 7 8 #include <stdint.h> 9 10 #include "include/cppgc/internal/gc-info.h" 11 #include "include/cppgc/platform.h" 12 #include "include/v8config.h" 13 #include "src/base/logging.h" 14 #include "src/base/macros.h" 15 #include "src/base/platform/mutex.h" 16 #include "src/base/platform/platform.h" 17 18 namespace cppgc { 19 namespace internal { 20 21 // GCInfo contains metadata for objects that are instantiated from classes that 22 // inherit from GarbageCollected. 23 struct GCInfo final { 24 FinalizationCallback finalize; 25 TraceCallback trace; 26 NameCallback name; 27 bool has_v_table; 28 }; 29 30 class V8_EXPORT GCInfoTable final { 31 public: 32 // At maximum |kMaxIndex - 1| indices are supported. 33 // 34 // We assume that 14 bits are enough to represent all possible types. 35 // 36 // For Blink during telemetry runs, we see about 1,000 different types; 37 // looking at the output of the Oilpan GC clang plugin, there appear to be at 38 // most about 6,000 types. Thus 14 bits should be more than twice as many bits 39 // as we will ever need. Different contexts may require adjusting this limit. 40 static constexpr GCInfoIndex kMaxIndex = 1 << 14; 41 42 // Minimum index returned. Values smaller |kMinIndex| may be used as 43 // sentinels. 44 static constexpr GCInfoIndex kMinIndex = 1; 45 46 // (Light) experimentation suggests that Blink doesn't need more than this 47 // while handling content on popular web properties. 48 static constexpr GCInfoIndex kInitialWantedLimit = 512; 49 50 // Refer through GlobalGCInfoTable for retrieving the global table outside 51 // of testing code. 52 explicit GCInfoTable(PageAllocator* page_allocator); 53 ~GCInfoTable(); 54 GCInfoTable(const GCInfoTable&) = delete; 55 GCInfoTable& operator=(const GCInfoTable&) = delete; 56 57 GCInfoIndex RegisterNewGCInfo(std::atomic<uint16_t>&, const GCInfo& info); 58 GCInfoFromIndex(GCInfoIndex index)59 const GCInfo& GCInfoFromIndex(GCInfoIndex index) const { 60 DCHECK_GE(index, kMinIndex); 61 DCHECK_LT(index, kMaxIndex); 62 DCHECK(table_); 63 return table_[index]; 64 } 65 NumberOfGCInfos()66 GCInfoIndex NumberOfGCInfos() const { return current_index_; } 67 LimitForTesting()68 GCInfoIndex LimitForTesting() const { return limit_; } TableSlotForTesting(GCInfoIndex index)69 GCInfo& TableSlotForTesting(GCInfoIndex index) { return table_[index]; } 70 allocator()71 PageAllocator* allocator() const { return page_allocator_; } 72 73 private: 74 void Resize(); 75 76 GCInfoIndex InitialTableLimit() const; 77 size_t MaxTableSize() const; 78 79 void CheckMemoryIsZeroed(uintptr_t* base, size_t len); 80 81 PageAllocator* page_allocator_; 82 // Holds the per-class GCInfo descriptors; each HeapObjectHeader keeps an 83 // index into this table. 84 GCInfo* table_; 85 uint8_t* read_only_table_end_; 86 // Current index used when requiring a new GCInfo object. 87 GCInfoIndex current_index_ = kMinIndex; 88 // The limit (exclusive) of the currently allocated table. 89 GCInfoIndex limit_ = 0; 90 91 v8::base::Mutex table_mutex_; 92 }; 93 94 class V8_EXPORT GlobalGCInfoTable final { 95 public: 96 GlobalGCInfoTable(const GlobalGCInfoTable&) = delete; 97 GlobalGCInfoTable& operator=(const GlobalGCInfoTable&) = delete; 98 99 // Sets up the table with the provided `page_allocator`. Will use an internal 100 // allocator in case no PageAllocator is provided. May be called multiple 101 // times with the same `page_allocator` argument. 102 static void Initialize(PageAllocator* page_allocator); 103 104 // Accessors for the singleton table. GetMutable()105 static GCInfoTable& GetMutable() { return *global_table_; } Get()106 static const GCInfoTable& Get() { return *global_table_; } 107 GCInfoFromIndex(GCInfoIndex index)108 static const GCInfo& GCInfoFromIndex(GCInfoIndex index) { 109 return Get().GCInfoFromIndex(index); 110 } 111 112 private: 113 // Singleton for each process. Retrieved through Get(). 114 static GCInfoTable* global_table_; 115 116 DISALLOW_NEW_AND_DELETE() 117 }; 118 119 } // namespace internal 120 } // namespace cppgc 121 122 #endif // V8_HEAP_CPPGC_GC_INFO_TABLE_H_ 123