org.bytedeco.tvm

Class DenseMapNode

java.lang.Object

org.bytedeco.javacpp.Pointer

org.bytedeco.tvm.TVMObject

org.bytedeco.tvm.MapNode

org.bytedeco.tvm.DenseMapNode

All Implemented Interfaces:

AutoCloseable

@Namespace(value="tvm::runtime")
 @NoOffset
 @Properties(inherit=tvm_runtime.class)
public class DenseMapNode
extends MapNode

\brief A specialization of hash map that implements the idea of array-based hash map. Another reference implementation can be found [1]. A. Overview DenseMapNode did several improvements over traditional separate chaining hash, in terms of cache locality, memory footprints and data organization. A1. Implicit linked list. For better cache locality, instead of using linked list explicitly for each bucket, we store list data into a single array that spans contiguously in memory, and then carefully design access patterns to make sure most of them fall into a single cache line. A2. 1-byte metadata. There is only 1 byte overhead for each slot in the array to indexing and traversal. This can be divided in 3 parts. 1) Reserved code: (0b11111111)_2 indicates a slot is empty; (0b11111110)_2 indicates protected, which means the slot is empty but not allowed to be written. 2) If not empty or protected, the highest bit is used to indicate whether data in the slot is head of a linked list. 3) The rest 7 bits are used as the "next pointer" (i.e. pointer to the next element). On 64-bit architecture, an ordinary pointer can take up to 8 bytes, which is not acceptable overhead when dealing with 16-byte ObjectRef pairs. Based on a commonly noticed fact that the lists are relatively short (length <= 3) in hash maps, we follow [1]'s idea that only allows the pointer to be one of the 126 possible values, i.e. if the next element of i-th slot is (i + x)-th element, then x must be one of the 126 pre-defined values. A3. Data blocking. We organize the array in the way that every 16 elements forms a data block. The 16-byte metadata of those 16 elements are stored together, followed by the real data, i.e. 16 key-value pairs. B. Implementation details B1. Power-of-2 table size and Fibonacci Hashing. We use power-of-two as table size to avoid modulo for more efficient arithmetics. To make the hash-to-slot mapping distribute more evenly, we use the Fibonacci Hashing [2] trick. B2. Traverse a linked list in the array. 1) List head. Assume Fibonacci Hashing maps a given key to slot i, if metadata at slot i indicates that it is list head, then we found the head; otherwise the list is empty. No probing is done in this procedure. 2) Next element. To find the next element of a non-empty slot i, we look at the last 7 bits of the metadata at slot i. If they are all zeros, then it is the end of list; otherwise, we know that the next element is (i + candidates[the-last-7-bits]). B3. InsertMaybeReHash an element. Following B2, we first traverse the linked list to see if this element is in the linked list, and if not, we put it at the end by probing the next empty position in one of the 126 candidate positions. If the linked list does not even exist, but the slot for list head has been occupied by another linked list, we should find this intruder another place. B4. Quadratic probing with triangle numbers. In open address hashing, it is provable that probing with triangle numbers can traverse power-of-2-sized table [3]. In our algorithm, we follow the suggestion in [1] that also use triangle numbers for "next pointer" as well as sparing for list head. [1] https://github.com/skarupke/flat_hash_map [2] https://programmingpraxis.com/2018/06/19/fibonacci-hash/ [3] https://fgiesen.wordpress.com/2015/02/22/triangular-numbers-mod-2n/

Nested Class Summary

Nested classes/interfaces inherited from class org.bytedeco.tvm.TVMObject

TVMObject.FDeleter

Nested classes/interfaces inherited from class org.bytedeco.javacpp.Pointer

Pointer.CustomDeallocator, Pointer.Deallocator, Pointer.NativeDeallocator, Pointer.ReferenceCounter

Field Summary

Fields inherited from class org.bytedeco.tvm.MapNode

_type_child_slots, _type_final, _type_index

Fields inherited from class org.bytedeco.tvm.TVMObject

_type_child_slots_can_overflow, _type_has_method_sequal_reduce, _type_has_method_shash_reduce, _type_has_method_visit_attrs

Fields inherited from class org.bytedeco.javacpp.Pointer

address, capacity, limit, position

Constructor Summary

Constructors

Constructor and Description
DenseMapNode() Default native constructor.
DenseMapNode(long size) Native array allocator.
DenseMapNode(Pointer p) Pointer cast constructor.

Method Summary

Modifier and Type	Method and Description
ObjectRef	at(ObjectRef key) \brief Index value associated with a key, throw exception if the key does not exist
Pointer	begin()
long	count(ObjectRef key) \brief Count the number of times a key exists in the hash map
Pointer	end()
void	erase(Pointer _position) \brief Erase the entry associated with the iterator
Pointer	find(ObjectRef key) \brief Index value associated with a key
DenseMapNode	getPointer(long i)
DenseMapNode	position(long position)

Methods inherited from class org.bytedeco.tvm.MapNode

_GetOrAllocRuntimeTypeIndex, _type_child_slots, _type_final, _type_index, _type_key, Empty, erase, RuntimeTypeIndex, size

Methods inherited from class org.bytedeco.tvm.TVMObject

_type_child_slots_can_overflow, _type_has_method_sequal_reduce, _type_has_method_shash_reduce, _type_has_method_visit_attrs, GetTypeKey, GetTypeKeyHash, put, type_index, TypeIndex2Key, TypeIndex2KeyHash, TypeKey2Index, TypeKey2Index, unique

Methods inherited from class org.bytedeco.javacpp.Pointer

address, asBuffer, asByteBuffer, availablePhysicalBytes, calloc, capacity, capacity, close, deallocate, deallocate, deallocateReferences, deallocator, deallocator, equals, fill, formatBytes, free, getDirectBufferAddress, getPointer, getPointer, getPointer, hashCode, interruptDeallocatorThread, isNull, isNull, limit, limit, malloc, maxBytes, maxPhysicalBytes, memchr, memcmp, memcpy, memmove, memset, offsetAddress, offsetof, offsetof, parseBytes, physicalBytes, physicalBytesInaccurate, position, put, realloc, referenceCount, releaseReference, retainReference, setNull, sizeof, sizeof, toString, totalBytes, totalCount, totalPhysicalBytes, withDeallocator, zero

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

DenseMapNode

public DenseMapNode()

Default native constructor.

DenseMapNode

public DenseMapNode(long size)

Native array allocator. Access with Pointer.position(long).

DenseMapNode

public DenseMapNode(Pointer p)

Pointer cast constructor. Invokes Pointer(Pointer).

Method Detail

position

public DenseMapNode position(long position)

Overrides:

position in class MapNode

getPointer

public DenseMapNode getPointer(long i)

Overrides:

getPointer in class MapNode

count

@Cast(value="size_t")
public long count(@Const @ByRef
                                         ObjectRef key)

Description copied from class: MapNode

\brief Count the number of times a key exists in the hash map

Overrides:

count in class MapNode

Parameters:

key - The indexing key

Returns:

The number of elements of the key

at

@ByRef
public ObjectRef at(@Const @ByRef
                            ObjectRef key)

\brief Index value associated with a key, throw exception if the key does not exist

Overrides:

at in class MapNode

Parameters:

key - The indexing key

Returns:

The mutable reference to the value

find

@ByVal
 @Cast(value="tvm::runtime::MapNode::iterator*")
public Pointer find(@Const @ByRef
                                                                              ObjectRef key)

\brief Index value associated with a key

Overrides:

find in class MapNode

Parameters:

key - The indexing key

Returns:

The iterator of the entry associated with the key, end iterator if not exists

erase

public void erase(@Cast(value="const tvm::runtime::MapNode::iterator*") @ByRef
                  Pointer _position)

\brief Erase the entry associated with the iterator

Overrides:

erase in class MapNode

Parameters:

position - The iterator

begin

@ByVal
 @Cast(value="tvm::runtime::MapNode::iterator*")
public Pointer begin()

Overrides:

begin in class MapNode

Returns:

begin iterator

end

@ByVal
 @Cast(value="tvm::runtime::MapNode::iterator*")
public Pointer end()

Overrides:

end in class MapNode

Returns:

end iterator