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// Copyright 2020 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_HEAP_CPPGC_GC_INFO_TABLE_H_
#define V8_HEAP_CPPGC_GC_INFO_TABLE_H_
#include <stdint.h>
#include "include/cppgc/internal/gc-info.h"
#include "include/cppgc/platform.h"
#include "include/v8config.h"
#include "src/base/logging.h"
#include "src/base/macros.h"
#include "src/base/platform/mutex.h"
#include "src/base/platform/platform.h"
namespace cppgc {
namespace internal {
// GCInfo contains metadata for objects that are instantiated from classes that
// inherit from GarbageCollected.
struct GCInfo final {
FinalizationCallback finalize;
TraceCallback trace;
NameCallback name;
bool has_v_table;
};
class V8_EXPORT GCInfoTable final {
public:
// At maximum |kMaxIndex - 1| indices are supported.
//
// We assume that 14 bits are enough to represent all possible types.
//
// For Blink during telemetry runs, we see about 1,000 different types;
// looking at the output of the Oilpan GC clang plugin, there appear to be at
// most about 6,000 types. Thus 14 bits should be more than twice as many bits
// as we will ever need. Different contexts may require adjusting this limit.
static constexpr GCInfoIndex kMaxIndex = 1 << 14;
// Minimum index returned. Values smaller |kMinIndex| may be used as
// sentinels.
static constexpr GCInfoIndex kMinIndex = 1;
// (Light) experimentation suggests that Blink doesn't need more than this
// while handling content on popular web properties.
static constexpr GCInfoIndex kInitialWantedLimit = 512;
// Refer through GlobalGCInfoTable for retrieving the global table outside
// of testing code.
explicit GCInfoTable(PageAllocator* page_allocator);
~GCInfoTable();
GCInfoTable(const GCInfoTable&) = delete;
GCInfoTable& operator=(const GCInfoTable&) = delete;
GCInfoIndex RegisterNewGCInfo(std::atomic<uint16_t>&, const GCInfo& info);
const GCInfo& GCInfoFromIndex(GCInfoIndex index) const {
DCHECK_GE(index, kMinIndex);
DCHECK_LT(index, kMaxIndex);
DCHECK(table_);
return table_[index];
}
GCInfoIndex NumberOfGCInfos() const { return current_index_; }
GCInfoIndex LimitForTesting() const { return limit_; }
GCInfo& TableSlotForTesting(GCInfoIndex index) { return table_[index]; }
PageAllocator* allocator() const { return page_allocator_; }
private:
void Resize();
GCInfoIndex InitialTableLimit() const;
size_t MaxTableSize() const;
void CheckMemoryIsZeroed(uintptr_t* base, size_t len);
PageAllocator* page_allocator_;
// Holds the per-class GCInfo descriptors; each HeapObjectHeader keeps an
// index into this table.
GCInfo* table_;
uint8_t* read_only_table_end_;
// Current index used when requiring a new GCInfo object.
GCInfoIndex current_index_ = kMinIndex;
// The limit (exclusive) of the currently allocated table.
GCInfoIndex limit_ = 0;
v8::base::Mutex table_mutex_;
};
class V8_EXPORT GlobalGCInfoTable final {
public:
GlobalGCInfoTable(const GlobalGCInfoTable&) = delete;
GlobalGCInfoTable& operator=(const GlobalGCInfoTable&) = delete;
// Sets up the table with the provided `page_allocator`. Will use an internal
// allocator in case no PageAllocator is provided. May be called multiple
// times with the same `page_allocator` argument.
static void Initialize(PageAllocator* page_allocator);
// Accessors for the singleton table.
static GCInfoTable& GetMutable() { return *global_table_; }
static const GCInfoTable& Get() { return *global_table_; }
static const GCInfo& GCInfoFromIndex(GCInfoIndex index) {
return Get().GCInfoFromIndex(index);
}
private:
// Singleton for each process. Retrieved through Get().
static GCInfoTable* global_table_;
DISALLOW_NEW_AND_DELETE()
};
} // namespace internal
} // namespace cppgc
#endif // V8_HEAP_CPPGC_GC_INFO_TABLE_H_
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