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/*
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* // Copyright (c) 1998, 2007, Oracle. All rights reserved.
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package oracle.toplink.essentials.internal.sessions;
import java.util.*;
import oracle.toplink.essentials.descriptors.ClassDescriptor;
/**
* This class calculates a commit order for a series of classes
* based on the dependencies between them. It builds up a graph of
* dependencies (CommitOrderDependencyNodes) then applies topological
* sort to them to get an ordering.
* This is a throwaway class, which exists only for the lifetime of
* the calculation.
*
* The algorithm is descrbied in the method comment for orderCommits().
* This class also includes static methods for quicksort, copied from
* the standard libraries and adapted for these objects, since that
* seemed like the easiest way to sort.
*/
public class CommitOrderCalculator {
protected int currentTime;
protected Vector nodes;
protected Vector orderedDescriptors;
protected AbstractSession session;
/**
*
*/
public CommitOrderCalculator(AbstractSession session) {
super();
this.currentTime = 0;
this.nodes = new Vector(1);
this.session = session;
}
protected void addNode(ClassDescriptor d) {
nodes.addElement(new CommitOrderDependencyNode(this, d, session));
}
public void addNodes(Vector descriptors) {
Enumeration descriptorsEnum = descriptors.elements();
while (descriptorsEnum.hasMoreElements()) {
ClassDescriptor descriptor = (ClassDescriptor)descriptorsEnum.nextElement();
addNode(descriptor);
}
}
/*
* Add to each node the dependent nodes
*/
public void calculateMappingDependencies() {
for (Enumeration e = nodes.elements(); e.hasMoreElements();) {
CommitOrderDependencyNode node = (CommitOrderDependencyNode)e.nextElement();
node.recordMappingDependencies();
}
}
/*
* Add to each node the dependent nodes
*/
public void calculateSpecifiedDependencies() {
for (Enumeration e = nodes.elements(); e.hasMoreElements();) {
CommitOrderDependencyNode node = (CommitOrderDependencyNode)e.nextElement();
node.recordSpecifiedDependencies();
}
}
public void depthFirstSearch() {
/*
* Traverse the entire graph in breadth-first order. When finished, every node will have a
* predecessor which indicates the node that came efore it in the search
* It will also have a discovery time (the value of the counter when we first saw it) and
* finishingTime (the value of the counter after we've visited all the adjacent nodes).
* See Cormen, Leiserson and Rivest, Section 23.3, page 477 for a full explanation of the algorithm
*/
//Setup
for (Enumeration e = getNodes().elements(); e.hasMoreElements();) {
CommitOrderDependencyNode node = (CommitOrderDependencyNode)e.nextElement();
node.markNotVisited();
node.setPredecessor(null);
}
currentTime = 0;
//Execution
for (Enumeration e = getNodes().elements(); e.hasMoreElements();) {
CommitOrderDependencyNode node = (CommitOrderDependencyNode)e.nextElement();
if (node.hasNotBeenVisited()) {
node.visit();
}
}
}
/* Support for quicksort */
/*
* Implement the doCompare method.
*/
private static int doCompare(Object o1, Object o2) {
// I don't care if they're equal, and I want to sort largest first.
int first;
// I don't care if they're equal, and I want to sort largest first.
int second;
first = ((CommitOrderDependencyNode)o1).getFinishingTime();
second = ((CommitOrderDependencyNode)o2).getFinishingTime();
if (first >= second) {
return 1;
} else {
return -1;
}
}
/* Support for quicksort */
/*
* Implement the doCompare method.
*/
private static int doCompare(CommitOrderDependencyNode o1, CommitOrderDependencyNode o2) {
// I don't care if they're equal, and I want to sort largest first.
int first;
// I don't care if they're equal, and I want to sort largest first.
int second;
first = o1.getFinishingTime();
second = o2.getFinishingTime();
if (first >= second) {
return 1;
} else {
return -1;
}
}
public int getNextTime() {
int result = currentTime;
currentTime++;
return result;
}
public Vector getNodes() {
return nodes;
}
/*
* Return the constraint ordered classes.
*/
public Vector getOrderedClasses() {
Vector orderedClasses = oracle.toplink.essentials.internal.helper.NonSynchronizedVector.newInstance(getOrderedDescriptors().size());
for (Enumeration orderedDescriptorsEnum = getOrderedDescriptors().elements();
orderedDescriptorsEnum.hasMoreElements();) {
orderedClasses.addElement(((ClassDescriptor)orderedDescriptorsEnum.nextElement()).getJavaClass());
}
return orderedClasses;
}
/*
* Return the constraint ordered descriptors.
*/
public Vector getOrderedDescriptors() {
return orderedDescriptors;
}
public CommitOrderDependencyNode nodeFor(Class c) {
for (Enumeration e = nodes.elements(); e.hasMoreElements();) {
CommitOrderDependencyNode n = (CommitOrderDependencyNode)e.nextElement();
if (n.getDescriptor().getJavaClass() == c) {
return n;
}
}
return null;
}
public CommitOrderDependencyNode nodeFor(ClassDescriptor d) {
for (Enumeration e = nodes.elements(); e.hasMoreElements();) {
CommitOrderDependencyNode n = (CommitOrderDependencyNode)e.nextElement();
if (n.getDescriptor() == d) {
return n;
}
}
return null;
}
/*
* Calculate the commit order.
* Do a depth first search on the graph, skipping nodes that we have
* already visited or are in the process of visiting. Keep a counter
* and note when we first encounter a node and when we finish visiting
* it. Once we've visited everything, sort nodes by finishing time
*/
public void orderCommits() {
depthFirstSearch();
Object[] nodeArray = new Object[nodes.size()];
nodes.copyInto(nodeArray);
quicksort(nodeArray);
Vector result = new Vector(nodes.size());
for (int i = 0; i < nodes.size(); i++) {
CommitOrderDependencyNode node = (CommitOrderDependencyNode)nodeArray[i];
result.addElement(node.getDescriptor());
}
this.orderedDescriptors = result;
}
/*
* Preform a sort using the specified comparitor object.
*/
private static void quicksort(Object[] arr) {
quicksort(arr, 0, arr.length - 1);
}
/*
* quicksort the array of objects.
*
* @param arr[] - an array of objects
* @param left - the start index - from where to begin sorting
* @param right - the last index.
*/
private static void quicksort(Object[] arr, int left, int right) {
int i;
int last;
if (left >= right) {/* do nothing if array contains fewer than two */
return;/* two elements */
}
swap(arr, left, (left + right) / 2);
last = left;
for (i = left + 1; i <= right; i++) {
if (doCompare(arr[i], arr[left]) < 0) {
swap(arr, ++last, i);
}
}
swap(arr, left, last);
quicksort(arr, left, last - 1);
quicksort(arr, last + 1, right);
}
private static void swap(Object[] arr, int i, int j) {
Object tmp;
tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
}
