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|
// Copyright 2018 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_OBJECTS_ORDERED_HASH_TABLE_H_
#define V8_OBJECTS_ORDERED_HASH_TABLE_H_
#include "src/globals.h"
#include "src/objects/fixed-array.h"
// Has to be the last include (doesn't have include guards):
#include "src/objects/object-macros.h"
namespace v8 {
namespace internal {
// Non-templatized base class for {OrderedHashTable}s.
// TODO(hash): Unify this with the HashTableBase above.
class OrderedHashTableBase : public FixedArray {
public:
static const int kNotFound = -1;
static const int kMinCapacity = 4;
static const int kNumberOfElementsIndex = 0;
// The next table is stored at the same index as the nof elements.
static const int kNextTableIndex = kNumberOfElementsIndex;
static const int kNumberOfDeletedElementsIndex = kNumberOfElementsIndex + 1;
static const int kNumberOfBucketsIndex = kNumberOfDeletedElementsIndex + 1;
static const int kHashTableStartIndex = kNumberOfBucketsIndex + 1;
static const int kRemovedHolesIndex = kHashTableStartIndex;
static constexpr const int kNumberOfElementsOffset =
FixedArray::OffsetOfElementAt(kNumberOfElementsIndex);
static constexpr const int kNextTableOffset =
FixedArray::OffsetOfElementAt(kNextTableIndex);
static constexpr const int kNumberOfDeletedElementsOffset =
FixedArray::OffsetOfElementAt(kNumberOfDeletedElementsIndex);
static constexpr const int kNumberOfBucketsOffset =
FixedArray::OffsetOfElementAt(kNumberOfBucketsIndex);
static constexpr const int kHashTableStartOffset =
FixedArray::OffsetOfElementAt(kHashTableStartIndex);
static const int kLoadFactor = 2;
// NumberOfDeletedElements is set to kClearedTableSentinel when
// the table is cleared, which allows iterator transitions to
// optimize that case.
static const int kClearedTableSentinel = -1;
};
// OrderedHashTable is a HashTable with Object keys that preserves
// insertion order. There are Map and Set interfaces (OrderedHashMap
// and OrderedHashTable, below). It is meant to be used by JSMap/JSSet.
//
// Only Object* keys are supported, with Object::SameValueZero() used as the
// equality operator and Object::GetHash() for the hash function.
//
// Based on the "Deterministic Hash Table" as described by Jason Orendorff at
// https://wiki.mozilla.org/User:Jorend/Deterministic_hash_tables
// Originally attributed to Tyler Close.
//
// Memory layout:
// [0]: element count
// [1]: deleted element count
// [2]: bucket count
// [3..(3 + NumberOfBuckets() - 1)]: "hash table", where each item is an
// offset into the data table (see below) where the
// first item in this bucket is stored.
// [3 + NumberOfBuckets()..length]: "data table", an array of length
// Capacity() * kEntrySize, where the first entrysize
// items are handled by the derived class and the
// item at kChainOffset is another entry into the
// data table indicating the next entry in this hash
// bucket.
//
// When we transition the table to a new version we obsolete it and reuse parts
// of the memory to store information how to transition an iterator to the new
// table:
//
// Memory layout for obsolete table:
// [0]: bucket count
// [1]: Next newer table
// [2]: Number of removed holes or -1 when the table was cleared.
// [3..(3 + NumberOfRemovedHoles() - 1)]: The indexes of the removed holes.
// [3 + NumberOfRemovedHoles()..length]: Not used
//
template <class Derived, int entrysize>
class OrderedHashTable : public OrderedHashTableBase {
public:
// Returns an OrderedHashTable with a capacity of at least |capacity|.
static Handle<Derived> Allocate(Isolate* isolate, int capacity,
PretenureFlag pretenure = NOT_TENURED);
// Returns an OrderedHashTable (possibly |table|) with enough space
// to add at least one new element.
static Handle<Derived> EnsureGrowable(Isolate* isolate,
Handle<Derived> table);
// Returns an OrderedHashTable (possibly |table|) that's shrunken
// if possible.
static Handle<Derived> Shrink(Isolate* isolate, Handle<Derived> table);
// Returns a new empty OrderedHashTable and records the clearing so that
// existing iterators can be updated.
static Handle<Derived> Clear(Isolate* isolate, Handle<Derived> table);
// Returns true if the OrderedHashTable contains the key
static bool HasKey(Isolate* isolate, Derived* table, Object* key);
// Returns a true value if the OrderedHashTable contains the key and
// the key has been deleted. This does not shrink the table.
static bool Delete(Isolate* isolate, Derived* table, Object* key);
int NumberOfElements() const {
return Smi::ToInt(get(kNumberOfElementsIndex));
}
int NumberOfDeletedElements() const {
return Smi::ToInt(get(kNumberOfDeletedElementsIndex));
}
// Returns the number of contiguous entries in the data table, starting at 0,
// that either are real entries or have been deleted.
int UsedCapacity() const {
return NumberOfElements() + NumberOfDeletedElements();
}
int NumberOfBuckets() const { return Smi::ToInt(get(kNumberOfBucketsIndex)); }
// Returns an index into |this| for the given entry.
int EntryToIndex(int entry) {
return kHashTableStartIndex + NumberOfBuckets() + (entry * kEntrySize);
}
int HashToBucket(int hash) { return hash & (NumberOfBuckets() - 1); }
int HashToEntry(int hash) {
int bucket = HashToBucket(hash);
Object* entry = this->get(kHashTableStartIndex + bucket);
return Smi::ToInt(entry);
}
int KeyToFirstEntry(Isolate* isolate, Object* key) {
// This special cases for Smi, so that we avoid the HandleScope
// creation below.
if (key->IsSmi()) {
uint32_t hash = ComputeUnseededHash(Smi::ToInt(key));
return HashToEntry(hash & Smi::kMaxValue);
}
HandleScope scope(isolate);
Object* hash = key->GetHash();
// If the object does not have an identity hash, it was never used as a key
if (hash->IsUndefined(isolate)) return kNotFound;
return HashToEntry(Smi::ToInt(hash));
}
int FindEntry(Isolate* isolate, Object* key) {
int entry = KeyToFirstEntry(isolate, key);
// Walk the chain in the bucket to find the key.
while (entry != kNotFound) {
Object* candidate_key = KeyAt(entry);
if (candidate_key->SameValueZero(key)) break;
entry = NextChainEntry(entry);
}
return entry;
}
int NextChainEntry(int entry) {
Object* next_entry = get(EntryToIndex(entry) + kChainOffset);
return Smi::ToInt(next_entry);
}
// use KeyAt(i)->IsTheHole(isolate) to determine if this is a deleted entry.
Object* KeyAt(int entry) {
DCHECK_LT(entry, this->UsedCapacity());
return get(EntryToIndex(entry));
}
bool IsObsolete() { return !get(kNextTableIndex)->IsSmi(); }
// The next newer table. This is only valid if the table is obsolete.
Derived* NextTable() { return Derived::cast(get(kNextTableIndex)); }
// When the table is obsolete we store the indexes of the removed holes.
int RemovedIndexAt(int index) {
return Smi::ToInt(get(kRemovedHolesIndex + index));
}
static const int kEntrySize = entrysize + 1;
static const int kChainOffset = entrysize;
static const int kMaxCapacity =
(FixedArray::kMaxLength - kHashTableStartIndex) /
(1 + (kEntrySize * kLoadFactor));
protected:
static Handle<Derived> Rehash(Isolate* isolate, Handle<Derived> table,
int new_capacity);
void SetNumberOfBuckets(int num) {
set(kNumberOfBucketsIndex, Smi::FromInt(num));
}
void SetNumberOfElements(int num) {
set(kNumberOfElementsIndex, Smi::FromInt(num));
}
void SetNumberOfDeletedElements(int num) {
set(kNumberOfDeletedElementsIndex, Smi::FromInt(num));
}
// Returns the number elements that can fit into the allocated buffer.
int Capacity() { return NumberOfBuckets() * kLoadFactor; }
void SetNextTable(Derived* next_table) { set(kNextTableIndex, next_table); }
void SetRemovedIndexAt(int index, int removed_index) {
return set(kRemovedHolesIndex + index, Smi::FromInt(removed_index));
}
};
class OrderedHashSet : public OrderedHashTable<OrderedHashSet, 1> {
public:
DECL_CAST(OrderedHashSet)
static Handle<OrderedHashSet> Add(Isolate* isolate,
Handle<OrderedHashSet> table,
Handle<Object> value);
static Handle<FixedArray> ConvertToKeysArray(Isolate* isolate,
Handle<OrderedHashSet> table,
GetKeysConversion convert);
static HeapObject* GetEmpty(ReadOnlyRoots ro_roots);
static inline int GetMapRootIndex();
static inline bool Is(Handle<HeapObject> table);
};
class OrderedHashMap : public OrderedHashTable<OrderedHashMap, 2> {
public:
DECL_CAST(OrderedHashMap)
// Returns a value if the OrderedHashMap contains the key, otherwise
// returns undefined.
static Handle<OrderedHashMap> Add(Isolate* isolate,
Handle<OrderedHashMap> table,
Handle<Object> key, Handle<Object> value);
Object* ValueAt(int entry);
static Object* GetHash(Isolate* isolate, Object* key);
static HeapObject* GetEmpty(ReadOnlyRoots ro_roots);
static inline int GetMapRootIndex();
static inline bool Is(Handle<HeapObject> table);
static const int kValueOffset = 1;
};
// This is similar to the OrderedHashTable, except for the memory
// layout where we use byte instead of Smi. The max capacity of this
// is only 254, we transition to an OrderedHashTable beyond that
// limit.
//
// Each bucket and chain value is a byte long. The padding exists so
// that the DataTable entries start aligned. A bucket or chain value
// of 255 is used to denote an unknown entry.
//
// Memory layout: [ Header ] [ Padding ] [ DataTable ] [ HashTable ] [ Chains ]
//
// The index are represented as bytes, on a 64 bit machine with
// kEntrySize = 1, capacity = 4 and entries = 2:
//
// [ Header ] :
// [0] : Number of elements
// [1] : Number of deleted elements
// [2] : Number of buckets
//
// [ Padding ] :
// [3 .. 7] : Padding
//
// [ DataTable ] :
// [8 .. 15] : Entry 1
// [16 .. 23] : Entry 2
// [24 .. 31] : empty
// [32 .. 39] : empty
//
// [ HashTable ] :
// [40] : First chain-link for bucket 1
// [41] : empty
//
// [ Chains ] :
// [42] : Next chain link for bucket 1
// [43] : empty
// [44] : empty
// [45] : empty
//
template <class Derived>
class SmallOrderedHashTable : public HeapObject {
public:
// Offset points to a relative location in the table
typedef int Offset;
// ByteIndex points to a index in the table that needs to be
// converted to an Offset.
typedef int ByteIndex;
void Initialize(Isolate* isolate, int capacity);
static Handle<Derived> Allocate(Isolate* isolate, int capacity,
PretenureFlag pretenure = NOT_TENURED);
// Returns a true if the OrderedHashTable contains the key
bool HasKey(Isolate* isolate, Handle<Object> key);
// Returns a true value if the table contains the key and
// the key has been deleted. This does not shrink the table.
static bool Delete(Isolate* isolate, Derived* table, Object* key);
// Returns an SmallOrderedHashTable (possibly |table|) with enough
// space to add at least one new element. Returns empty handle if
// we've already reached MaxCapacity.
static MaybeHandle<Derived> Grow(Isolate* isolate, Handle<Derived> table);
static Handle<Derived> Rehash(Isolate* isolate, Handle<Derived> table,
int new_capacity);
// Iterates only fields in the DataTable.
class BodyDescriptor;
// No weak fields.
typedef BodyDescriptor BodyDescriptorWeak;
// Returns total size in bytes required for a table of given
// capacity.
static int SizeFor(int capacity) {
DCHECK_GE(capacity, kMinCapacity);
DCHECK_LE(capacity, kMaxCapacity);
int data_table_size = DataTableSizeFor(capacity);
int hash_table_size = capacity / kLoadFactor;
int chain_table_size = capacity;
int total_size = kDataTableStartOffset + data_table_size + hash_table_size +
chain_table_size;
return RoundUp(total_size, kPointerSize);
}
// Returns the number elements that can fit into the allocated table.
int Capacity() const {
int capacity = NumberOfBuckets() * kLoadFactor;
DCHECK_GE(capacity, kMinCapacity);
DCHECK_LE(capacity, kMaxCapacity);
return capacity;
}
// Returns the number elements that are present in the table.
int NumberOfElements() const {
int nof_elements = getByte(kNumberOfElementsOffset, 0);
DCHECK_LE(nof_elements, Capacity());
return nof_elements;
}
int NumberOfDeletedElements() const {
int nof_deleted_elements = getByte(kNumberOfDeletedElementsOffset, 0);
DCHECK_LE(nof_deleted_elements, Capacity());
return nof_deleted_elements;
}
int NumberOfBuckets() const { return getByte(kNumberOfBucketsOffset, 0); }
DECL_VERIFIER(SmallOrderedHashTable)
static const int kMinCapacity = 4;
static const byte kNotFound = 0xFF;
// We use the value 255 to indicate kNotFound for chain and bucket
// values, which means that this value can't be used a valid
// index.
static const int kMaxCapacity = 254;
STATIC_ASSERT(kMaxCapacity < kNotFound);
// The load factor is used to derive the number of buckets from
// capacity during Allocation. We also depend on this to calaculate
// the capacity from number of buckets after allocation. If we
// decide to change kLoadFactor to something other than 2, capacity
// should be stored as another field of this object.
static const int kLoadFactor = 2;
// Our growth strategy involves doubling the capacity until we reach
// kMaxCapacity, but since the kMaxCapacity is always less than 256,
// we will never fully utilize this table. We special case for 256,
// by changing the new capacity to be kMaxCapacity in
// SmallOrderedHashTable::Grow.
static const int kGrowthHack = 256;
protected:
void SetDataEntry(int entry, int relative_index, Object* value);
// TODO(gsathya): Calculate all the various possible values for this
// at compile time since capacity can only be 4 different values.
Offset GetBucketsStartOffset() const {
int capacity = Capacity();
int data_table_size = DataTableSizeFor(capacity);
return kDataTableStartOffset + data_table_size;
}
Address GetHashTableStartAddress(int capacity) const {
return FIELD_ADDR(this, kDataTableStartOffset + DataTableSizeFor(capacity));
}
void SetFirstEntry(int bucket, byte value) {
DCHECK_LE(static_cast<unsigned>(bucket), NumberOfBuckets());
setByte(GetBucketsStartOffset(), bucket, value);
}
int GetFirstEntry(int bucket) const {
DCHECK_LE(static_cast<unsigned>(bucket), NumberOfBuckets());
return getByte(GetBucketsStartOffset(), bucket);
}
// TODO(gsathya): Calculate all the various possible values for this
// at compile time since capacity can only be 4 different values.
Offset GetChainTableOffset() const {
int nof_buckets = NumberOfBuckets();
int capacity = nof_buckets * kLoadFactor;
DCHECK_EQ(Capacity(), capacity);
int data_table_size = DataTableSizeFor(capacity);
int hash_table_size = nof_buckets;
return kDataTableStartOffset + data_table_size + hash_table_size;
}
void SetNextEntry(int entry, int next_entry) {
DCHECK_LT(static_cast<unsigned>(entry), Capacity());
DCHECK_GE(static_cast<unsigned>(next_entry), 0);
DCHECK(next_entry <= Capacity() || next_entry == kNotFound);
setByte(GetChainTableOffset(), entry, next_entry);
}
int GetNextEntry(int entry) const {
DCHECK_LT(entry, Capacity());
return getByte(GetChainTableOffset(), entry);
}
Object* GetDataEntry(int entry, int relative_index) {
DCHECK_LT(entry, Capacity());
DCHECK_LE(static_cast<unsigned>(relative_index), Derived::kEntrySize);
Offset entry_offset = GetDataEntryOffset(entry, relative_index);
return READ_FIELD(this, entry_offset);
}
Object* KeyAt(int entry) const {
DCHECK_LT(entry, Capacity());
Offset entry_offset = GetDataEntryOffset(entry, Derived::kKeyIndex);
return READ_FIELD(this, entry_offset);
}
int HashToBucket(int hash) const { return hash & (NumberOfBuckets() - 1); }
int HashToFirstEntry(int hash) const {
int bucket = HashToBucket(hash);
int entry = GetFirstEntry(bucket);
DCHECK(entry < Capacity() || entry == kNotFound);
return entry;
}
void SetNumberOfBuckets(int num) { setByte(kNumberOfBucketsOffset, 0, num); }
void SetNumberOfElements(int num) {
DCHECK_LE(static_cast<unsigned>(num), Capacity());
setByte(kNumberOfElementsOffset, 0, num);
}
void SetNumberOfDeletedElements(int num) {
DCHECK_LE(static_cast<unsigned>(num), Capacity());
setByte(kNumberOfDeletedElementsOffset, 0, num);
}
int FindEntry(Isolate* isolate, Object* key) {
DisallowHeapAllocation no_gc;
Object* hash = key->GetHash();
if (hash->IsUndefined(isolate)) return kNotFound;
int entry = HashToFirstEntry(Smi::ToInt(hash));
// Walk the chain in the bucket to find the key.
while (entry != kNotFound) {
Object* candidate_key = KeyAt(entry);
if (candidate_key->SameValueZero(key)) return entry;
entry = GetNextEntry(entry);
}
return kNotFound;
}
static const Offset kNumberOfElementsOffset = kHeaderSize;
static const Offset kNumberOfDeletedElementsOffset =
kNumberOfElementsOffset + kOneByteSize;
static const Offset kNumberOfBucketsOffset =
kNumberOfDeletedElementsOffset + kOneByteSize;
static const constexpr Offset kDataTableStartOffset =
RoundUp<kPointerSize>(kNumberOfBucketsOffset);
static constexpr int DataTableSizeFor(int capacity) {
return capacity * Derived::kEntrySize * kPointerSize;
}
// This is used for accessing the non |DataTable| part of the
// structure.
byte getByte(Offset offset, ByteIndex index) const {
DCHECK(offset < kDataTableStartOffset || offset >= GetBucketsStartOffset());
return READ_BYTE_FIELD(this, offset + (index * kOneByteSize));
}
void setByte(Offset offset, ByteIndex index, byte value) {
DCHECK(offset < kDataTableStartOffset || offset >= GetBucketsStartOffset());
WRITE_BYTE_FIELD(this, offset + (index * kOneByteSize), value);
}
Offset GetDataEntryOffset(int entry, int relative_index) const {
DCHECK_LT(entry, Capacity());
int offset_in_datatable = entry * Derived::kEntrySize * kPointerSize;
int offset_in_entry = relative_index * kPointerSize;
return kDataTableStartOffset + offset_in_datatable + offset_in_entry;
}
int UsedCapacity() const {
int used = NumberOfElements() + NumberOfDeletedElements();
DCHECK_LE(used, Capacity());
return used;
}
private:
friend class OrderedHashMapHandler;
friend class OrderedHashSetHandler;
friend class CodeStubAssembler;
};
class SmallOrderedHashSet : public SmallOrderedHashTable<SmallOrderedHashSet> {
public:
DECL_CAST(SmallOrderedHashSet)
DECL_PRINTER(SmallOrderedHashSet)
static const int kKeyIndex = 0;
static const int kEntrySize = 1;
// Adds |value| to |table|, if the capacity isn't enough, a new
// table is created. The original |table| is returned if there is
// capacity to store |value| otherwise the new table is returned.
static MaybeHandle<SmallOrderedHashSet> Add(Isolate* isolate,
Handle<SmallOrderedHashSet> table,
Handle<Object> key);
static inline bool Is(Handle<HeapObject> table);
static inline int GetMapRootIndex();
};
class SmallOrderedHashMap : public SmallOrderedHashTable<SmallOrderedHashMap> {
public:
DECL_CAST(SmallOrderedHashMap)
DECL_PRINTER(SmallOrderedHashMap)
static const int kKeyIndex = 0;
static const int kValueIndex = 1;
static const int kEntrySize = 2;
// Adds |value| to |table|, if the capacity isn't enough, a new
// table is created. The original |table| is returned if there is
// capacity to store |value| otherwise the new table is returned.
static MaybeHandle<SmallOrderedHashMap> Add(Isolate* isolate,
Handle<SmallOrderedHashMap> table,
Handle<Object> key,
Handle<Object> value);
static inline bool Is(Handle<HeapObject> table);
static inline int GetMapRootIndex();
};
// TODO(gsathya): Rename this to OrderedHashTable, after we rename
// OrderedHashTable to LargeOrderedHashTable. Also set up a
// OrderedHashSetBase class as a base class for the two tables and use
// that instead of a HeapObject here.
template <class SmallTable, class LargeTable>
class OrderedHashTableHandler {
public:
typedef int Entry;
static Handle<HeapObject> Allocate(Isolate* isolate, int capacity);
static bool Delete(Handle<HeapObject> table, Handle<Object> key);
static bool HasKey(Isolate* isolate, Handle<HeapObject> table,
Handle<Object> key);
// TODO(gsathya): Move this to OrderedHashTable
static const int OrderedHashTableMinSize =
SmallOrderedHashTable<SmallTable>::kGrowthHack << 1;
};
class OrderedHashMapHandler
: public OrderedHashTableHandler<SmallOrderedHashMap, OrderedHashMap> {
public:
static Handle<HeapObject> Add(Isolate* isolate, Handle<HeapObject> table,
Handle<Object> key, Handle<Object> value);
static Handle<OrderedHashMap> AdjustRepresentation(
Isolate* isolate, Handle<SmallOrderedHashMap> table);
};
class OrderedHashSetHandler
: public OrderedHashTableHandler<SmallOrderedHashSet, OrderedHashSet> {
public:
static Handle<HeapObject> Add(Isolate* isolate, Handle<HeapObject> table,
Handle<Object> key);
static Handle<OrderedHashSet> AdjustRepresentation(
Isolate* isolate, Handle<SmallOrderedHashSet> table);
};
class JSCollectionIterator : public JSObject {
public:
// [table]: the backing hash table mapping keys to values.
DECL_ACCESSORS(table, Object)
// [index]: The index into the data table.
DECL_ACCESSORS(index, Object)
// Dispatched behavior.
DECL_PRINTER(JSCollectionIterator)
static const int kTableOffset = JSObject::kHeaderSize;
static const int kIndexOffset = kTableOffset + kPointerSize;
static const int kSize = kIndexOffset + kPointerSize;
private:
DISALLOW_IMPLICIT_CONSTRUCTORS(JSCollectionIterator);
};
// OrderedHashTableIterator is an iterator that iterates over the keys and
// values of an OrderedHashTable.
//
// The iterator has a reference to the underlying OrderedHashTable data,
// [table], as well as the current [index] the iterator is at.
//
// When the OrderedHashTable is rehashed it adds a reference from the old table
// to the new table as well as storing enough data about the changes so that the
// iterator [index] can be adjusted accordingly.
//
// When the [Next] result from the iterator is requested, the iterator checks if
// there is a newer table that it needs to transition to.
template <class Derived, class TableType>
class OrderedHashTableIterator : public JSCollectionIterator {
public:
// Whether the iterator has more elements. This needs to be called before
// calling |CurrentKey| and/or |CurrentValue|.
bool HasMore();
// Move the index forward one.
void MoveNext() { set_index(Smi::FromInt(Smi::ToInt(index()) + 1)); }
// Returns the current key of the iterator. This should only be called when
// |HasMore| returns true.
inline Object* CurrentKey();
private:
// Transitions the iterator to the non obsolete backing store. This is a NOP
// if the [table] is not obsolete.
void Transition();
DISALLOW_IMPLICIT_CONSTRUCTORS(OrderedHashTableIterator);
};
} // namespace internal
} // namespace v8
#include "src/objects/object-macros-undef.h"
#endif // V8_OBJECTS_ORDERED_HASH_TABLE_H_
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