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LockFreeBPBSTMap.java
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LockFreeBPBSTMap.java
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package algorithms.published;
/*
The Batched Persistent Non-Blocking Binary Search Tree
This is an optimized version of PNB-BST algorithm that supports key batching in the leafs.
Copyright (C) 2019 Elias Papavasileiou
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater; // For CAS operations
import java.util.concurrent.atomic.AtomicInteger; // For atomic increments of counter
/**
Represents a Persistent Non-Blocking Binary Search Tree (PNB-BST)
*/
public class LockFreeBPBSTMap<K extends Comparable<? super K>, V> {
private final int BATCHING_DEGREE;
public LockFreeBPBSTMap(final int BATCHING_DEGREE) {
this.BATCHING_DEGREE = BATCHING_DEGREE;
}
public LockFreeBPBSTMap() {
this.BATCHING_DEGREE = 16;
}
/**
Represents a PNB-BST node.
*/
private static final class Node<X extends Comparable<? super X>, Y> {
private X key; // The unique key of this node (for Internals)
private X[] keys; // The unique keys of this node (for Leafs)
private Y[] values; // Data that map to keys (for Leafs)
private int size; // Number of keys stored in this node (for Leafs)
volatile Node<X,Y> leftChild; // Reference to the left child of this node
volatile Node<X,Y> rightChild; // Reference to the right child of this node
private Node<X,Y> prevNode; // Reference to the node replaced by this node
volatile Info<X,Y> info; // Reference to the Info object that this node belongs
private int versionSeq; // The sequence number of this node
/**
Private constructor. Used by others to create
either a Leaf or an Internal PNB-BST node.
*/
private Node(final X key, final X[] keys, final Y[] values, final int size, final Node<X,Y> leftChild,
final Node<X,Y> rightChild, final Node<X,Y> prevNode, final Info<X,Y> info, final int versionSeq) {
this.key = key;
this.keys = keys;
this.values = values;
this.size = size;
this.leftChild = leftChild;
this.rightChild = rightChild;
this.prevNode = prevNode;
this.info = info;
this.versionSeq = versionSeq;
}
/**
Creates a Leaf node.
*/
Node(final X[] keys, final Y[] values, final int size, final Node<X,Y> prevNode,
final Info<X,Y> info, final int versionSeq) {
this(null, keys, values, size, null, null, prevNode, info, versionSeq);
}
/**
Creates an Internal node.
*/
Node(final X key, final Node<X,Y> leftChild, final Node<X,Y> rightChild,
final Node<X,Y> prevNode, final Info<X,Y> info, final int versionSeq) {
this(key, null, null, 0, leftChild, rightChild, prevNode, info, versionSeq);
}
/**
Creates an empty node.
*/
Node(final X[] keys, final Y[] values) {
this(null, keys, values, 0, null, null, null, null, 0);
}
/**
Checks if this node is frozen for an Info object.
@param info the info object for which to check this node's frozen status
@return true if this node if frozen for the provided info, false otherwise
*/
private final boolean frozen(final Info<X,Y> info) {
return ((info.state == State.NULL || info.state == State.TRY) // Operation is in progress - needs help
|| (info.isMarked(this) && info.state == State.COMMIT)); // This node is deleted from the tree
}
final int getSize() {
return size;
}
final void setAll(final X[] keys, final Y[] values, final int size,
final Node<X,Y> prevNode, final Info<X,Y> info, final int versionSeq) {
this.keys = keys;
this.values = values;
this.size = size;
this.prevNode = prevNode;
this.info = info;
this.versionSeq = versionSeq;
}
final void setAll(final X key, final Node<X,Y> leftChild, final Node<X,Y> rightChild,
final Node<X,Y> prevNode, final Info<X,Y> info, final int versionSeq) {
this.key = key;
this.leftChild = leftChild;
this.rightChild = rightChild;
this.prevNode = prevNode;
this.info = info;
this.versionSeq = versionSeq;
}
final void setAll(final int size, final Node<X,Y> prevNode, final Info<X,Y> info, final int versionSeq) {
this.size = size;
this.prevNode = prevNode;
this.info = info;
this.versionSeq = versionSeq;
}
final void clearAll() {
this.key = null;
this.size = 0;
this.leftChild = null;
this.rightChild = null;
this.prevNode = null;
this.info = null;
this.versionSeq = 0;
}
private boolean isFull(int maxSize) {
return (size == maxSize);
}
private boolean hasOnlyOneKey() {
return (keys != null && size == 1);
}
/**
Performs a binary search of key in this node's array of keys.
Precondition: key cannot be null.
@param key the key to search for
@return the index of key if it was found, otherwise -1
*/
private final int containsKey(final X key) {
int i, a = 0, b = size-1;
do {
i = (a+b)/2;
if (key.compareTo(keys[i]) == 0)
return i;
else if (key.compareTo(keys[i]) < 0)
b = i-1;
else
a = i+1;
} while (a <= b);
return -1;
}
/**
Adds all keys of this node that belong in range [a,b] to ret.
@param a the lower limit of the range
@param b the upper limit of the range
@param ret the stack where keys are saved
*/
private final void gatherKeys(final X a, final X b, final RangeScanResultHolder.Stack<Y> ret) {
if (keys == null)
return;
// Initialize helper indices
int startIndex = 0, endIndex = size-1;
// Locate first and last key to return
while (a.compareTo(keys[startIndex]) > 0 && startIndex != endIndex)
startIndex++;
while (b.compareTo(keys[endIndex]) < 0 && endIndex != startIndex)
endIndex--;
// Add all keys between them to the range query result
for (int i = startIndex; i <= endIndex; i++)
ret.push(values[i]);
}
/**
Checks if key should be put in the left half of this node's array of keys.
*/
private boolean shouldBePutLeft(final X key) {
return (keys == null || key.compareTo(keys[size/2]) < 0);
}
/**
Copies all keys of this node plus key in newNode.
*/
private final void put(final X key, final Y value,
final Node<X,Y> prevNode, final Info<X,Y> info,
final int versionSeq, final Node<X,Y> newNode) {
int i, a = 0, b = size-1;
do {
i = (a+b)/2;
if (key.compareTo(keys[i]) < 0)
b = i-1;
else
a = i+1;
} while (a <= b);
newNode.setAll(size+1, prevNode, info, versionSeq);
System.arraycopy(keys, 0, newNode.keys, 0, a);
System.arraycopy(values, 0, newNode.values, 0, a);
newNode.keys[a] = key;
newNode.values[a] = value;
System.arraycopy(keys, a, newNode.keys, a+1, size-a);
System.arraycopy(values, a, newNode.values, a+1, size-a);
}
/**
Copies all keys of this node except key in newNode.
*/
private final void remove(final X key, final Node<X,Y> prevNode, final Info<X,Y> info,
final int versionSeq, final Node<X,Y> newNode) {
int i, a = 0, b = size-1;
do {
i = (a+b)/2;
if (key.compareTo(keys[i]) < 0)
b = i-1;
else
a = i+1;
} while (a <= b);
newNode.setAll(size-1, prevNode, info, versionSeq);
System.arraycopy(keys, 0, newNode.keys, 0, b);
System.arraycopy(values, 0, newNode.values, 0, b);
System.arraycopy(keys, b+1, newNode.keys, b, size-b-1);
System.arraycopy(values, b+1, newNode.values, b, size-b-1);
}
/**
Copies the left half of this node's array of keys plus key in newNode.
*/
private final void splitLeftAndPut(final X key, final Y value, final Node<X,Y> prevNode,
final Info<X,Y> info, final int versionSeq, final Node<X,Y> newNode) {
int newSize = (size/2)+1;
int i, a = 0, b = newSize-1;
do {
i = (a+b)/2;
if (key.compareTo(keys[i]) < 0)
b = i-1;
else
a = i+1;
} while (a <= b);
newNode.setAll(newSize, prevNode, info, versionSeq);
System.arraycopy(keys, 0, newNode.keys, 0, a);
System.arraycopy(values, 0, newNode.values, 0, a);
newNode.keys[a] = key;
newNode.values[a] = value;
System.arraycopy(keys, a, newNode.keys, a+1, newSize-1-a);
System.arraycopy(values, a, newNode.values, a+1, newSize-1-a);
}
/**
Copies the right half of this node's array of keys plus key in newNode.
*/
private final void splitRightAndPut(final X key, final Y value, final Node<X,Y> prevNode,
final Info<X,Y> info, final int versionSeq, final Node<X,Y> newNode) {
int newSize = (size/2)+1;
int newStart = (size+1)/2;
int i, a = newSize-1, b = size-1;
do {
i = (a+b)/2;
if (key.compareTo(keys[i]) < 0)
b = i-1;
else
a = i+1;
} while (a <= b);
newNode.setAll(newSize, prevNode, info, versionSeq);
System.arraycopy(this.keys, newStart, newNode.keys, 0, a-newStart);
System.arraycopy(this.values, newStart, newNode.values, 0, a-newStart);
newNode.keys[a-newStart] = key;
newNode.values[a-newStart] = value;
System.arraycopy(this.keys, a, newNode.keys, a-newStart+1, size-a);
System.arraycopy(this.values, a, newNode.values, a-newStart+1, size-a);
}
/**
Copies the left half of this node's array of keys in newNode.
*/
private final void splitLeft(final Node<X,Y> prevNode, final Info<X,Y> info,
final int versionSeq, final Node<X,Y> newNode) {
int newSize = (size+1)/2;
newNode.setAll(newSize, prevNode, info, versionSeq);
System.arraycopy(this.keys, 0, newNode.keys, 0, newSize);
System.arraycopy(this.values, 0, newNode.values, 0, newSize);
}
/**
Copies the right half of this node's array of keys in newNode.
*/
private final void splitRight(final Node<X,Y> prevNode, final Info<X,Y> info,
final int versionSeq, final Node<X,Y> newNode) {
int newSize = (size+1)/2;
newNode.setAll(newSize, prevNode, info, versionSeq);
System.arraycopy(this.keys, size-newSize, newNode.keys, 0, newSize);
System.arraycopy(this.values, size-newSize, newNode.values, 0, newSize);
}
}
/**
Represents the possible states that an Info object can be in.
NULL: The procedure of updating a child pointer of the first node
is in progress, but the handshaking has not been performed yet.
TRY: The procedure of updating a child pointer of the first node
is in progress, and the handshaking has completed successfully.
COMMIT: The marked nodes have been deleted and the first node is idle.
ABORT: All nodes are idle.
*/
private enum State {
NULL, TRY, COMMIT, ABORT
}
/**
Represents an Info object.
*/
private static final class Info<X extends Comparable<? super X>, Y> {
// The state of this Info object
volatile State state;
// Node whose child pointer will be updated
// Connects the newNode to the tree
private Node<X,Y> connectorNode;
// Nodes to be deleted (marked nodes)
private Node<X,Y> firstMarkedNode; // Used in Insert and Delete
private Node<X,Y> secondMarkedNode; // Used in Delete only
private Node<X,Y> thirdMarkedNode; // Used in Delete only
// Saved info references of marked nodes
// Used as expected values in info CAS
private Info<X,Y> firstMarkedOldInfo; // Used in Insert and Delete
private Info<X,Y> secondMarkedOldInfo; // Used in Delete only
private Info<X,Y> thirdMarkedOldInfo; // Used in Delete only
// Node to be connected to the tree
// Can be the Internal of the new triad (on Insert)
// or the new sibling (on Delete)
// Used as update value in child CAS
private Node<X,Y> newNode;
// Sequence number of the Insert or Delete operation
// Used for handshaking
private int handshakingSeq;
/**
Creates an Info object for a Delete operation.
*/
Info(final State state, final Node<X,Y> connectorNode,
final Node<X,Y> firstMarkedNode, final Node<X,Y> secondMarkedNode, final Node<X,Y> thirdMarkedNode,
final Info<X,Y> firstMarkedOldInfo, final Info<X,Y> secondMarkedOldInfo, final Info<X,Y> thirdMarkedOldInfo,
final Node<X,Y> newNode, final int handshakingSeq) {
this.state = state;
this.connectorNode = connectorNode;
this.firstMarkedNode = firstMarkedNode;
this.secondMarkedNode = secondMarkedNode;
this.thirdMarkedNode = thirdMarkedNode;
this.firstMarkedOldInfo = firstMarkedOldInfo;
this.secondMarkedOldInfo = secondMarkedOldInfo;
this.thirdMarkedOldInfo = thirdMarkedOldInfo;
this.newNode = newNode;
this.handshakingSeq = handshakingSeq;
}
/**
Creates an Info object for an Insert operation.
*/
Info(final State state, final Node<X,Y> connectorNode, final Node<X,Y> firstMarkedNode,
final Info<X,Y> firstMarkedOldInfo, final Node<X,Y> newNode, final int handshakingSeq) {
this(state, connectorNode, firstMarkedNode, null, null, firstMarkedOldInfo, null, null, newNode, handshakingSeq);
}
/**
Checks if the node is marked for this Info object.
@param node the node to check its mark status
*/
private boolean isMarked(final Node<X,Y> node) {
return (this.firstMarkedNode == node || this.secondMarkedNode == node || this.thirdMarkedNode == node);
}
}
// Updater objects, used for CAS operations
private static final AtomicReferenceFieldUpdater<Node, Node> leftChildUpdater =
AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "leftChild");
private static final AtomicReferenceFieldUpdater<Node, Node> rightChildUpdater =
AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "rightChild");
private static final AtomicReferenceFieldUpdater<Node, Info> infoUpdater =
AtomicReferenceFieldUpdater.newUpdater(Node.class, Info.class, "info");
private static final AtomicReferenceFieldUpdater<Info, State> stateUpdater =
AtomicReferenceFieldUpdater.newUpdater(Info.class, State.class, "state");
// Global version counter
private AtomicInteger counter = new AtomicInteger(0);
// The Dummy Info object
private static final Info dummy = new Info(State.ABORT, null, null, null, null, null, null, null, null, 0);
// To avoid handling special case when the tree contains <= 2 nodes,
// 2 dummy nodes (children of root) are created that both contain key null.
// All real keys inside PBST are required to be non-null
private final Node<K,V> root = new Node<K,V>(null, new Node<K,V>(null, null, 0, null, dummy, 0),
new Node<K,V>(null, null, 0, null, dummy, 0), null, dummy, 0);
// Reference to thread local variables that are used by
// ValidateLeaf and ValidateLink to return the result of a validation
private final ThreadLocal<ValidationResultHolder> validationResult = new ThreadLocal<ValidationResultHolder>() {
@Override
protected ValidationResultHolder initialValue() {
return new ValidationResultHolder<K,V>();
}
};
// Reference to a thread local variable that is used by
// RangeScan to return the result of a range query
private final ThreadLocal<RangeScanResultHolder> rangeScanResult = new ThreadLocal<RangeScanResultHolder>() {
@Override
protected RangeScanResultHolder initialValue() {
return new RangeScanResultHolder<K,V>();
}
};
// Reference to thread local variables that are used by
// putIfAbsent to create one new triad per successful call
private final ThreadLocal<InsertTriadHolder> insertTriad = new ThreadLocal<InsertTriadHolder>() {
@Override
protected InsertTriadHolder initialValue() {
return new InsertTriadHolder<K,V>(BATCHING_DEGREE);
}
};
// Reference to a thread local variable that is used by
// putIfAbsent and remove to create one new leaf per successful call
private final ThreadLocal<UpdatedLeafHolder> updatedLeaf = new ThreadLocal<UpdatedLeafHolder>() {
@Override
protected UpdatedLeafHolder initialValue() {
return new UpdatedLeafHolder<K,V>(BATCHING_DEGREE);
}
};
// Reference to thread local variables that are used by
// remove to create one new copy of sibling per successful call
private final ThreadLocal<SiblingCopyHolder> siblingCopy = new ThreadLocal<SiblingCopyHolder>() {
@Override
protected SiblingCopyHolder initialValue() {
return new SiblingCopyHolder<K,V>();
}
};
// Reference to thread local variable that is used by
// executeInsert and executeDelete to reuse info objects
private final ThreadLocal<InfoObjectHolder> infoObject = new ThreadLocal<InfoObjectHolder>() {
@Override
protected InfoObjectHolder initialValue() {
return new InfoObjectHolder<K,V>();
}
};
/**
Represents a storage space where the result of a validation operation is saved
Each thread gets a copy of these variables
*/
private static final class ValidationResultHolder<X extends Comparable<? super X>, Y> {
private ValidateLeafResult<X,Y> gp_p_l_link;
private ValidateLinkResult<X,Y> gp_p_link;
private ValidateLinkResult<X,Y> p_l_link;
private ValidateLinkResult<X,Y> p_s_link;
private ValidateLinkResult<X,Y> s_newLeft_link;
private ValidateLinkResult<X,Y> s_newRight_link;
ValidationResultHolder() {
gp_p_l_link = new ValidateLeafResult<X,Y>(false, null, null);
gp_p_link = new ValidateLinkResult<X,Y>(false, null);
p_l_link = new ValidateLinkResult<X,Y>(false, null);
p_s_link = new ValidateLinkResult<X,Y>(false, null);
s_newLeft_link = new ValidateLinkResult<X,Y>(false, null);
s_newRight_link = new ValidateLinkResult<X,Y>(false, null);
}
private static final class ValidateLinkResult<X extends Comparable<? super X>, Y> {
boolean validated;
Info<X,Y> info;
ValidateLinkResult(boolean validated, Info<X,Y> info) {
this.validated = validated;
this.info = info;
}
}
private static final class ValidateLeafResult<X extends Comparable<? super X>, Y> {
boolean validated;
Info<X,Y> gpinfo;
Info<X,Y> pinfo;
ValidateLeafResult(boolean validated, Info<X,Y> gpinfo, Info<X,Y> pinfo) {
this.validated = validated;
this.gpinfo = gpinfo;
this.pinfo = pinfo;
}
}
}
/**
Represents a storage space where the result of a range query operation is saved
Each thread gets a copy of this variable
*/
private static final class RangeScanResultHolder<X extends Comparable<? super X>, Y> {
private Stack<Y> rsResult;
RangeScanResultHolder() {
rsResult = new Stack<Y>();
}
private static final class Stack<Y> {
private final int INIT_SIZE = 128;
private Object[] stackArray;
private int head = 0;
Stack() {
stackArray = new Object[INIT_SIZE];
}
final void clear() {
head = 0;
}
final Object[] getStackArray() {
return stackArray;
}
final int getEffectiveSize() {
return head;
}
final void push(final Y x) {
if (head == stackArray.length) {
final Object[] newStackArray = new Object[stackArray.length*4];
System.arraycopy(stackArray, 0, newStackArray, 0, head);
stackArray = newStackArray;
}
stackArray[head] = x;
++head;
}
}
}
/**
Represents a storage space where the new nodes created by putIfAbsent are saved
Each thread gets a copy of these variables
*/
private static final class InsertTriadHolder<X extends Comparable<? super X>, Y> {
private Node<X,Y> newInternal;
private Node<X,Y> newLeaf;
private Node<X,Y> newSibling;
InsertTriadHolder(int BATCHING_DEGREE) {
// New triad
newLeaf = new Node<X,Y>((X[]) new Comparable[BATCHING_DEGREE], (Y[]) new Object[BATCHING_DEGREE]);
newSibling = new Node<X,Y>((X[]) new Comparable[BATCHING_DEGREE], (Y[]) new Object[BATCHING_DEGREE]);
newInternal = new Node<X,Y>(null, null);
}
}
/**
Represents a storage space where the new leaf created by putIfAbsent and remove are saved
Each thread gets a copy of these variables
*/
private static final class UpdatedLeafHolder<X extends Comparable<? super X>, Y> {
private Node<X,Y> newLeaf;
UpdatedLeafHolder(int BATCHING_DEGREE) {
newLeaf = new Node<X,Y>((X[]) new Comparable[BATCHING_DEGREE], (Y[]) new Object[BATCHING_DEGREE]);
}
}
/**
Represents a storage space where the new sibling created by remove is saved
Each thread gets a copy of this variable
*/
private static final class SiblingCopyHolder<X extends Comparable<? super X>, Y> {
private Node<X,Y> newSibling;
SiblingCopyHolder() {
newSibling = new Node<X,Y>(null, null);
}
}
/**
Represents a storage space where the new info object created by executeInsert or executeDelete is saved
Each thread gets a copy of this variable
*/
private static final class InfoObjectHolder<X extends Comparable<? super X>, Y> {
private Info<X,Y> info;
private boolean shallCreateNewInfo;
InfoObjectHolder() {
info = null;
shallCreateNewInfo = true;
}
void refreshInsertInfo(final State state, final Node<X,Y> connectorNode, final Node<X,Y> firstMarkedNode,
final Info<X,Y> firstMarkedOldInfo, final Node<X,Y> newNode, final int handshakingSeq) {
refreshInfo(state, connectorNode, firstMarkedNode, null, null, firstMarkedOldInfo,
null, null, newNode, handshakingSeq);
}
void refreshDeleteInfo(final State state, final Node<X,Y> connectorNode, final Node<X,Y> firstMarkedNode,
final Node<X,Y> secondMarkedNode, final Node<X,Y> thirdMarkedNode,
final Info<X,Y> firstMarkedOldInfo, final Info<X,Y> secondMarkedOldInfo,
final Info<X,Y> thirdMarkedOldInfo, final Node<X,Y> newNode, final int handshakingSeq) {
refreshInfo(state, connectorNode, firstMarkedNode, secondMarkedNode, thirdMarkedNode,
firstMarkedOldInfo, secondMarkedOldInfo, thirdMarkedOldInfo, newNode, handshakingSeq);
}
private void refreshInfo(final State state, final Node<X,Y> connectorNode,
final Node<X,Y> firstMarkedNode, final Node<X,Y> secondMarkedNode, final Node<X,Y> thirdMarkedNode,
final Info<X,Y> firstMarkedOldInfo, final Info<X,Y> secondMarkedOldInfo, final Info<X,Y> thirdMarkedOldInfo,
final Node<X,Y> newNode, final int handshakingSeq) {
info.state = state;
info.connectorNode = connectorNode;
info.firstMarkedNode = firstMarkedNode;
info.secondMarkedNode = secondMarkedNode;
info.thirdMarkedNode = thirdMarkedNode;
info.firstMarkedOldInfo = firstMarkedOldInfo;
info.secondMarkedOldInfo = secondMarkedOldInfo;
info.thirdMarkedOldInfo = thirdMarkedOldInfo;
info.newNode = newNode;
info.handshakingSeq = handshakingSeq;
}
}
/**
Implements the Find operation.
<p>
Precondition: key cannot be null.
@param key the key whose presence in this map is to be tested
@return true if this map contains a mapping for the specified key
*/
public final boolean containsKey(final K key) {
// Precondition
if (key == null) throw new IllegalArgumentException("Key cannot be null.");
// Get validationResultHolder before the start of making attempts
ValidationResultHolder validationResultHolder = validationResult.get();
// Search variables
int seq;
Node<K,V> ggp = null, gp, p, l;
// Start making search attempts
while (true) {
seq = counter.get(); // Update sequence number
// Optimization - if ggp is not frozen, resume search from there
if (ggp != null && !ggp.frozen(ggp.info)) {
p = ggp;
l = readChild(p, p.key == null || key.compareTo(p.key) < 0, seq);
}
else { // Restart search from root
p = root;
l = root.leftChild;
}
ggp = null;
gp = null;
// Search for the leaf that may contain key
while (l.leftChild != null) {
ggp = gp;
gp = p;
p = l;
l = readChild(p, p.key == null || key.compareTo(p.key) < 0, seq);
}
// After resuming from ggp, in case the nodes pointed by p and l are deleted
// before the search starts, gp will be null but p will not point to the root node
// (instead, it will point to the old ggp which, in the general case, is not the root).
// This state is unacceptable, thus search must be restarted from root.
if (gp == null && p != root) continue;
// Perform validation
validateLeaf(gp, p, l, key, validationResultHolder);
//return (l.keys != null && l.containsKey(key) != -1);
// Proceed only if validation was successful
if (validationResultHolder.gp_p_l_link.validated) {
boolean ret = (l.keys != null && l.containsKey(key) != -1);
// System.out.println(ret ? "[*] Successful find: " + key : "[*] Unsuccessful find: " + key);
return ret;
}
}
}
/**
Implements the Insert operation.
<p>
Precondition: key cannot be null.
@param key the key with which the specified value is to be associated
@param value the value to be associated with the specified key
@return the previous value associated with the specified key,
or null if there was no mapping for the key.
*/
public final V putIfAbsent(final K key, final V value) {
// Preconditions
if (key == null) throw new IllegalArgumentException("Key cannot be null.");
// Get thread local variables before the start of making attempts
ValidationResultHolder validationResultHolder = validationResult.get();
InsertTriadHolder insertTriadHolder = insertTriad.get();
UpdatedLeafHolder updatedLeafHolder = updatedLeaf.get();
// Search variables
int seq;
Node<K,V> ggp = null, gp, p, l;
// Start making insert attempts
while (true) {
seq = counter.get(); // Update sequence number
// Optimization - if ggp is not frozen, resume search from there
if (ggp != null && !ggp.frozen(ggp.info)) {
p = ggp;
l = readChild(p, p.key == null || key.compareTo(p.key) < 0, seq);
}
else { // Restart search from root
p = root;
l = root.leftChild;
}
ggp = null;
gp = null;
// Search for the leaf that may contain key
while (l.leftChild != null) {
ggp = gp;
gp = p;
p = l;
l = readChild(p, p.key == null || key.compareTo(p.key) < 0, seq);
}
// After resuming from ggp, in case the nodes pointed by p and l are deleted
// before the search starts, gp will be null but p will not point to the root node
// (instead, it will point to the old ggp which, in the general case, is not the root).
// This state is unacceptable, thus search must be restarted from root.
if (gp == null && p != root) continue;
// Perform validation
validateLeaf(gp, p, l, key, validationResultHolder);
// Proceed only if validation was successful
if (validationResultHolder.gp_p_l_link.validated) {
if (l.keys != null && l.containsKey(key) != -1) {
// System.out.println("[*] Unsuccessful insert: " + key);
return value; // Unsuccessful Insert
}
// Optimization - extra handshaking check
if (counter.get() != seq) continue;
insertTriadHolder.newLeaf.clearAll();
insertTriadHolder.newSibling.clearAll();
insertTriadHolder.newInternal.clearAll();
if (l.keys == null) { // Special case - insert the very first node
insertTriadHolder.newLeaf.setAll(1, null, dummy, seq);
insertTriadHolder.newLeaf.keys[0] = key;
insertTriadHolder.newLeaf.values[0] = value;
insertTriadHolder.newSibling.setAll(null, null, 0, null, dummy, seq);
insertTriadHolder.newInternal.setAll(null, insertTriadHolder.newLeaf,
insertTriadHolder.newSibling, l, dummy, seq);
// Attempt insertion
if (executeInsert(p, l, validationResultHolder.gp_p_l_link.pinfo,
l.info, insertTriadHolder.newInternal, seq)) {
// System.out.println("[*] Successful insert: " + key);
insertTriad.remove();
return null; // Successful Insert
}
}
else if (l.isFull(BATCHING_DEGREE)) {
// Create new triad
if (l.shouldBePutLeft(key)) {
l.splitLeftAndPut(key, value, null, dummy, seq, insertTriadHolder.newLeaf);
l.splitRight(null, dummy, seq, insertTriadHolder.newSibling);
insertTriadHolder.newInternal.setAll(insertTriadHolder.newSibling.keys[0],
insertTriadHolder.newLeaf,
insertTriadHolder.newSibling, l, dummy, seq);
}
else {
l.splitRightAndPut(key, value, null, dummy, seq, insertTriadHolder.newLeaf);
l.splitLeft(null, dummy, seq, insertTriadHolder.newSibling);
insertTriadHolder.newInternal.setAll(insertTriadHolder.newLeaf.keys[0],
insertTriadHolder.newSibling,
insertTriadHolder.newLeaf, l, dummy, seq);
}
// Attempt insertion
if (executeInsert(p, l, validationResultHolder.gp_p_l_link.pinfo,
l.info, insertTriadHolder.newInternal, seq)) {
// System.out.println("[*] Successful insert: " + key);
insertTriad.remove();
return null; // Successful Insert
}
}
else {
l.put(key, value, l, dummy, seq, updatedLeafHolder.newLeaf);
// Attempt insertion
if (executeInsert(p, l, validationResultHolder.gp_p_l_link.pinfo,
l.info, updatedLeafHolder.newLeaf, seq)) {
// System.out.println("[*] Successful insert: " + key);
updatedLeaf.remove();
return null; // Successful Insert
}
}
}
}
}
/**
Implements the Delete operation.
<p>
Precondition: key cannot be null.
@param key the key whose mapping is to be removed from the map
@return the previous value associated with the specified key,
or null if there was no mapping for the key.
*/
public final V remove(final K key) {
// Preconditions
if (key == null) throw new IllegalArgumentException("Key cannot be null.");
// Get thread local variables before the start of making attempts
ValidationResultHolder validationResultHolder = validationResult.get();
SiblingCopyHolder siblingCopyHolder = siblingCopy.get();
UpdatedLeafHolder updatedLeafHolder = updatedLeaf.get();
// Search variables
int seq;
Node<K,V> ggp = null, gp, p, l;
// Helpers
Node<K,V> sibling;
Info<K,V> sinfo;
boolean validated = false;
// Start making delete attempts
while (true) {
seq = counter.get(); // Update sequence number
// Optimization - if ggp is not frozen, resume search from there
if (ggp != null && !ggp.frozen(ggp.info)) {
p = ggp;
l = readChild(p, p.key == null || key.compareTo(p.key) < 0, seq);
}
else { // Restart search from root
p = root;
l = root.leftChild;
}
ggp = null;
gp = null;
// Search for the leaf that may contain key
while (l.leftChild != null) {
ggp = gp;
gp = p;
p = l;
l = readChild(p, p.key == null || key.compareTo(p.key) < 0, seq);
}
// After resuming from ggp, in case the nodes pointed by p and l are deleted
// before the search starts, gp will be null but p will not point to the root node
// (instead, it will point to the old ggp which, in the general case, is not the root).
// This state is unacceptable, thus search must be restarted from root.
if (gp == null && p != root) continue;
// Perform validation
validateLeaf(gp, p, l, key, validationResultHolder);
// Proceed only if validation was successful
if (validationResultHolder.gp_p_l_link.validated) {
if (l.keys == null || l.containsKey(key) == -1) {
// System.out.println("[*] Unsuccessful delete: " + key);
return null; // Unsuccessful Delete
}
updatedLeafHolder.newLeaf.clearAll();
siblingCopyHolder.newSibling.clearAll();
if (l.hasOnlyOneKey()) {
//System.out.println("[*] hasOnlyOneKey !");
// Validate sibling
sibling = readChild(p, p.key != null && (l.keys[0]).compareTo(p.key) >= 0, seq);
validateLink(p, sibling, p.key != null && (l.keys[0]).compareTo(p.key) >= 0, validationResultHolder.p_s_link);
validated = validationResultHolder.p_s_link.validated;
if (validated) {
// Optimization - extra handshaking check
if (counter.get() != seq) continue;
// Create new sibling
if (sibling.leftChild == null) { // Sibling is Leaf
//System.out.println("[" + Thread.currentThread().getId() + "] Sibling is Leaf !");
siblingCopyHolder.newSibling.setAll(sibling.keys, sibling.values, sibling.getSize(),
p, sibling.info, seq);
sinfo = sibling.info;
}
else { // Sibling is Internal, validate its children
//System.out.println("[" + Thread.currentThread().getId() + "] Sibling is Internal !");
siblingCopyHolder.newSibling.setAll(sibling.key, sibling.leftChild, sibling.rightChild,
p, sibling.info, seq);
validateLink(sibling, siblingCopyHolder.newSibling.leftChild,
true, validationResultHolder.s_newLeft_link);
validated = validationResultHolder.s_newLeft_link.validated;
sinfo = validationResultHolder.s_newLeft_link.info;
if (validated) {
validateLink(sibling, siblingCopyHolder.newSibling.rightChild,
false, validationResultHolder.s_newRight_link);
validated = validationResultHolder.s_newRight_link.validated;
}
}
// Attempt deletion
if (validated && executeDelete(gp, p, l, sibling, validationResultHolder.gp_p_l_link.gpinfo,
validationResultHolder.gp_p_l_link.pinfo, l.info, sinfo,
siblingCopyHolder.newSibling, seq)) {
// System.out.println("[*] Successful delete: " + key);
siblingCopy.remove();
return l.values[0]; // Successful Delete
}
}
}
else {
//System.out.println("[" + Thread.currentThread().getId() + "] has many keys !");
l.remove(key, l, dummy, seq, updatedLeafHolder.newLeaf);
// Attempt deletion
if (executeInsert(p, l, validationResultHolder.gp_p_l_link.pinfo,
l.info, updatedLeafHolder.newLeaf, seq)) {
// System.out.println("[*] Successful delete: " + key);
updatedLeaf.remove();
return l.values[0]; // Successful Delete
}
}
}
}
}
/**
Implements the RangeScan operation.
<p>
Preconditions:
<ul>
<li> a and b cannot be null
<li> a is less than or equal to b
<ul>
@param a the lower limit of the range
@param b the upper limit of the range
@return all values of mappings with keys in range [a,b]
*/
public final Object[] rangeScan(final K a, final K b) {
// Preconditions
if (a == null) throw new IllegalArgumentException("a cannot be null.");
if (b == null) throw new IllegalArgumentException("b cannot be null.");
if (a.compareTo(b) > 0) throw new IllegalArgumentException("a cannot be bigger than b");
int seq = counter.get(); // Get a sequence number
counter.incrementAndGet(); // Increment global version counter
// Get and initialize rangeScanResultHolder before starting the tree traversal
RangeScanResultHolder rangeScanResultHolder = rangeScanResult.get();
rangeScanResultHolder.rsResult.clear();
// Start the tree traversal
scanHelper(root, seq, a, b, rangeScanResultHolder.rsResult);
// Get stack and its number of elements
Object[] stackArray = rangeScanResultHolder.rsResult.getStackArray();
int stackSize = rangeScanResultHolder.rsResult.getEffectiveSize();
// Make a copy of the stack and return it
Object[] returnArray = new Object[stackSize];
System.arraycopy(stackArray, 0, returnArray, 0, stackSize);