org.coweb.oe.HistoryBuffer Maven / Gradle / Ivy
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package org.coweb.oe;
import java.util.Collection;
import java.util.HashMap;
import java.util.Vector;
import java.util.Stack;
import java.util.Arrays;
import java.util.Comparator;
import java.util.logging.Logger;
public class HistoryBuffer {
private static final Logger log = Logger.getLogger(HistoryBuffer.class
.getName());
private HashMap ops = null;
private int size = 0;
public HistoryBuffer() {
this.ops = new HashMap();
this.size = 0;
}
@Override
public String toString() {
StringBuffer b = new StringBuffer();
b.append("{ops : " + this.ops);
b.append(",size : " + this.size);
b.append("}");
return b.toString();
}
/**
* Serializes the history buffer contents to seed a remote instance.
*
* @return {Object[]} Serialized operations in the history
*/
public Object[] getState() {
Vector v = new Vector();
Operation op = null;
for(String key : this.ops.keySet()) {
op = this.ops.get(key);
v.addElement(op.getState());
}
return v.toArray();
}
/**
* Unserializes history buffer contents to initialize this instance.
*
* @param arr Array in the format returned by getState
*/
public void setState(Object[] arr) {
// reset internals
this.size = 0;
this.ops.clear();
for(int i=0; i < arr.length; i++) {
// restore operations
Operation op = null;
try {
op = Operation.createOperationFromState((Object[])arr[i]);
this.addLocal(op);
}
catch(OperationEngineException e) { ; }
}
}
/**
* Retrieves all of the operations represented by the given context
* differences from the history buffer. Sorts them by total order, placing
* any ops with an unknown place in the order (i.e., local ops) at the end
* sorted by their sequence IDs. Throws an exception when a requested
* operation is missing from the history.
*
* @param cd Context difference object
* @throws OperationEngineException
* @return Sorted operations
*/
public Stack getOpsForDifference(ContextDifference cd) throws OperationEngineException {
// get the ops
String[] keys = cd.getHistoryBufferKeys();
Vector opsStack = new Vector();
int l = keys.length;
String key;
Operation op;
for(int i=0; i < l; i++) {
log.info("key = " + keys[i]);
key = keys[i];
op = this.ops.get(key);
if(op == null) {
throw new OperationEngineException("missing op for context diff: i=" + i +
" key=" + key + " keys=" + keys.toString());
}
opsStack.addElement(op);
}
// sort by total order
Operation[] arr = new Operation[opsStack.size()];
arr = opsStack.toArray(arr);
Arrays.sort(arr, new Comparator() {
public int compare(Operation a, Operation b) {
return a.compareByOrder(b);
}
});
Stack stack = new Stack();
stack.addAll(Arrays.asList(arr));
return stack;
}
/**
* Adds a local operation to the history.
*
* @param op Local operation to add
*/
public void addLocal(Operation op) {
String key = Operation.createHistoryKey(op.siteId, op.seqId);
this.ops.put(key, op);
// make sure ops in the history never change
op.immutable = true;
++this.size;
}
/**
* Adds a received operation to the history. If the operation already
* exists in the history, simply updates its order attribute. If not,
* adds it. Throws an exception if the op does not include its place in
* the total order or if the op with the same key already has an assigned
* place in the total order.
*
* @param op Received operation to add
* @throws OperationEngineException
*/
public void addRemote(Operation op) throws OperationEngineException {
String key = Operation.createHistoryKey(op.siteId, op.seqId);
Operation eop = this.ops.get(key);
if(op.order == Operation.infinity) {
// remote op must have order set by server
throw new OperationEngineException("remote op missing total order");
} else if(eop != null) {
if(eop.order != Operation.infinity) {
// order should never repeat
throw new OperationEngineException("duplicate op in total order: old="+eop.order +
" new="+op.order);
}
// server has responded with known total order for an op this site
// previously sent; update the local op with the info
eop.order = op.order;
} else {
// add new remote op to history
this.ops.put(key, op);
op.immutable = true;
++this.size;
}
}
/**
* Removes and returns an operation in the history.
*
* @param op Operation to locate for removal
* @return Removed operation
*/
public Operation remove(Operation op) {
String key = Operation.createHistoryKey(op.siteId, op.seqId);
op = this.ops.remove(key);
// no longer in the history, so allow mutation
op.immutable = false;
--this.size;
return op;
}
/**
* Gets the number of operations in the history.
*
* @return Integer count
*/
public int getCount() {
return this.size;
}
/**
* Gets all operations in the history buffer sorted by context.
*
* @return Sorted operations
*/
public Stack getContextSortedOperations() {
Collection collection = this.ops.values();
Operation[] arr = new Operation[collection.size()];
arr = collection.toArray(arr);
Arrays.sort(arr, new Comparator() {
public int compare(Operation a, Operation b) {
return a.compareByContext(b);
}
});
Stack stack = new Stack();
stack.addAll(Arrays.asList(arr));
return stack;
}
}