package client.net.sf.saxon.ce.value;
import client.net.sf.saxon.ce.Controller;
import client.net.sf.saxon.ce.event.SequenceOutputter;
import client.net.sf.saxon.ce.event.SequenceReceiver;
import client.net.sf.saxon.ce.event.TeeOutputter;
import client.net.sf.saxon.ce.expr.LastPositionFinder;
import client.net.sf.saxon.ce.expr.XPathContext;
import client.net.sf.saxon.ce.om.*;
import client.net.sf.saxon.ce.tree.iter.ArrayIterator;
import client.net.sf.saxon.ce.tree.iter.EmptyIterator;
import client.net.sf.saxon.ce.tree.iter.GroundedIterator;
import client.net.sf.saxon.ce.tree.iter.SingletonIterator;
import client.net.sf.saxon.ce.trans.XPathException;
import java.util.List;
/**
* A MemoClosure represents a value that has not yet been evaluated: the value is represented
* by an expression, together with saved values of all the context variables that the
* expression depends on.
* <p/>
* <p>The MemoClosure is designed for use when the value is only read several times. The
* value is saved on the first evaluation and remembered for later use.</p>
* <p/>
* <p>The MemoClosure maintains a reservoir containing those items in the value that have
* already been read. When a new iterator is requested to read the value, this iterator
* first examines and returns any items already placed in the reservoir by previous
* users of the MemoClosure. When the reservoir is exhausted, it then uses an underlying
* Input Iterator to read further values of the underlying expression. If the value is
* not read to completion (for example, if the first user did exists($expr), then the
* Input Iterator is left positioned where this user abandoned it. The next user will read
* any values left in the reservoir by the first user, and then pick up iterating the
* base expression where the first user left off. Eventually, all the values of the
* expression will find their way into the reservoir, and future users simply iterate
* over the reservoir contents. Alternatively, of course, the values may be left unread.</p>
* <p/>
* <p>Delayed evaluation is used only for expressions with a static type that allows
* more than one item, so the evaluateItem() method will not normally be used, but it is
* supported for completeness.</p>
* <p/>
* <p>The expression may depend on local variables and on the context item; these values
* are held in the saved XPathContext object that is kept as part of the Closure, and they
* will always be read from that object. The expression may also depend on global variables;
* these are unchanging, so they can be read from the Bindery in the normal way. Expressions
* that depend on other contextual information, for example the values of position(), last(),
* current(), current-group(), should not be evaluated using this mechanism: they should
* always be evaluated eagerly. This means that the Closure does not need to keep a copy
* of these context variables.</p>
* <p/>
* <p>In Saxon-EE, a for-each loop can be multithreaded. If a variable declared outside
* the loop is evaluated as a MemoClosure, then a reference to the variable within the
* loop can result in concurrent attempts to evaluate the variable incrementally. This
* is prevented by synchronizing the evaluation methods.</p>
*/
public class MemoClosure extends Closure {
transient private Item[] reservoir = null;
private int used;
protected int state;
// State in which no items have yet been read
private static final int UNREAD = 0;
// State in which zero or more items are in the reservoir and it is not known
// whether more items exist
private static final int MAYBE_MORE = 1;
// State in which all the items are in the reservoir
private static final int ALL_READ = 3;
// State in which we are getting the base iterator. If the closure is called in this state,
// it indicates a recursive entry, which is only possible on an error path
private static final int BUSY = 4;
// State in which we know that the value is an empty sequence
protected static final int EMPTY = 5;
/**
* Constructor should not be called directly, instances should be made using the make() method.
*/
public MemoClosure() {
//System.err.println("Creating MemoClosure");
}
/**
* Evaluate the expression in a given context to return an iterator over a sequence
*
*/
public synchronized SequenceIterator iterate() throws XPathException {
switch (state) {
case UNREAD:
state = BUSY;
inputIterator = expression.iterate(savedXPathContext);
if (inputIterator instanceof EmptyIterator) {
state = EMPTY;
return inputIterator;
}
// TODO: following optimization looks OK, but it throws func20 into an infinite loop
// if (inputIterator instanceof GroundedIterator) {
// state = UNREAD;
// return inputIterator.getAnother();
// }
reservoir = new Item[50];
used = 0;
state = MAYBE_MORE;
return new ProgressiveIterator();
case MAYBE_MORE:
return new ProgressiveIterator();
case ALL_READ:
switch (used) {
case 0:
state = EMPTY;
return EmptyIterator.getInstance();
case 1:
return SingletonIterator.makeIterator(reservoir[0]);
default:
return new ArrayIterator(reservoir, 0, used);
}
case BUSY:
// recursive entry: can happen if there is a circularity involving variable and function definitions
// Can also happen if variable evaluation is attempted in a debugger, hence the cautious message
XPathException de = new XPathException("Attempt to access a variable while it is being evaluated");
de.setErrorCode("XTDE0640");
//de.setXPathContext(context);
throw de;
case EMPTY:
return EmptyIterator.getInstance();
default:
throw new IllegalStateException("Unknown iterator state");
}
}
/**
* Process the expression by writing the value to the current Receiver
*
* @param context The dynamic context, giving access to the current node,
* the current variables, etc.
*/
public synchronized void process(XPathContext context) throws XPathException {
// To evaluate the closure in push mode, we need to use the original context of the
// expression for everything except the current output destination, which is taken from the
// context supplied at evaluation time
if (state == EMPTY) {
return; // we know there is nothing to do
} else if (state == BUSY) {
// recursive entry: can happen if there is a circularity involving variable and function definitions
XPathException de = new XPathException("Attempt to access a variable while it is being evaluated");
de.setErrorCode("XTDE0640");
de.setXPathContext(context);
throw de;
}
if (reservoir != null) {
SequenceIterator iter = iterate();
SequenceReceiver out = context.getReceiver();
while (true) {
Item it = iter.next();
if (it==null) break;
out.append(it, NodeInfo.ALL_NAMESPACES);
}
} else {
state = BUSY;
Controller controller = context.getController();
XPathContext c2 = savedXPathContext.newMinorContext();
//c2.setOrigin(this);
// Fork the output: one copy goes to a SequenceOutputter which remembers the contents for
// use next time the variable is referenced; another copy goes to the current output destination.
SequenceOutputter seq = controller.allocateSequenceOutputter(20);
seq.setPipelineConfiguration(controller.makePipelineConfiguration());
seq.open();
TeeOutputter tee = new TeeOutputter(context.getReceiver(), seq);
tee.setPipelineConfiguration(controller.makePipelineConfiguration());
c2.setTemporaryReceiver(tee);
expression.process(c2);
seq.close();
List list = seq.getList();
if (list.isEmpty()) {
state = EMPTY;
} else {
reservoir = new Item[list.size()];
reservoir = (Item[])list.toArray(reservoir);
used = list.size();
state = ALL_READ;
}
// give unwanted stuff to the garbage collector
savedXPathContext = null;
seq.reset();
}
}
/**
* Get the n'th item in the sequence (starting from 0). This is defined for all
* SequenceValues, but its real benefits come for a SequenceValue stored extensionally
*/
public synchronized Item itemAt(int n) throws XPathException {
if (n < 0) {
return null;
}
if (reservoir != null && n < used) {
return reservoir[n];
}
if (state == ALL_READ || state == EMPTY) {
return null;
}
if (state == UNREAD) {
return super.itemAt(n);
// this will read from the start of the sequence
}
// We have read some items from the input sequence but not enough. Read as many more as are needed.
int diff = n - used + 1;
while (diff-- > 0) {
Item i = inputIterator.next();
if (i == null) {
state = ALL_READ;
condense();
return itemAt(n);
}
append(i);
state = MAYBE_MORE;
}
//noinspection ConstantConditions
return reservoir[n];
}
/**
* Get the length of the sequence
*/
public int getLength() throws XPathException {
if (state == ALL_READ) {
return used;
} else if (state == EMPTY) {
return 0;
} else {
return super.getLength();
}
}
/**
* Append an item to the reservoir
* @param item the item to be added
*/
private void append(Item item) {
if (used >= reservoir.length) {
Item[] r2 = new Item[used*2];
System.arraycopy(reservoir, 0, r2, 0, used);
reservoir = r2;
}
reservoir[used++] = item;
}
/**
* Release unused space in the reservoir (provided the amount of unused space is worth reclaiming)
*/
private void condense() {
if (reservoir.length - used > 30) {
Item[] r2 = new Item[used];
System.arraycopy(reservoir, 0, r2, 0, used);
reservoir = r2;
}
// give unwanted stuff to the garbage collector
savedXPathContext = null;
// inputIterator = null;
// expression = null;
}
/**
* Determine whether the contents of the MemoClosure have been fully read
* @return true if the contents have been fully read
*/
public boolean isFullyRead() {
return state==EMPTY || state==ALL_READ;
}
/**
* Return a value containing all the items in the sequence returned by this
* SequenceIterator
*
* @return the corresponding value
*/
public Value materialize() throws XPathException {
if (state == ALL_READ) {
return new SequenceExtent(reservoir, 0, used);
} else if (state == EMPTY) {
return EmptySequence.getInstance();
}
return new SequenceExtent(iterate());
}
/**
* A ProgressiveIterator starts by reading any items already held in the reservoir;
* when the reservoir is exhausted, it reads further items from the inputIterator,
* copying them into the reservoir as they are read.
*/
public final class ProgressiveIterator implements SequenceIterator, LastPositionFinder, GroundedIterator {
int position = -1; // zero-based position in the reservoir of the
// item most recently read
/**
* Create a ProgressiveIterator
*/
public ProgressiveIterator() {
}
public Item next() throws XPathException {
if (position == -2) { // means we've already returned null once, keep doing so if called again.
return null;
}
if (++position < used) {
return reservoir[position];
} else if (state == ALL_READ) {
// someone else has read the input to completion in the meantime
position = -2;
return null;
} else {
Item i = inputIterator.next();
if (i == null) {
state = ALL_READ;
condense();
position = -2;
return null;
}
position = used;
append(i);
state = MAYBE_MORE;
return i;
}
}
public Item current() {
if (position < 0) {
return null;
}
return reservoir[position];
}
public int position() {
return position + 1; // return one-based position
}
public SequenceIterator getAnother() {
return new ProgressiveIterator();
}
/**
* Get the last position (that is, the number of items in the sequence)
*/
public int getLastPosition() throws XPathException {
if (state == ALL_READ) {
return used;
} else if (state == EMPTY) {
return 0;
} else {
// save the current position
int savePos = position;
// fill the reservoir
while (true) {
Item item = next();
if (item == null) {
break;
}
}
// reset the current position
position = savePos;
// return the total number of items
return used;
}
}
/**
* Return a value containing all the items in the sequence returned by this
* SequenceIterator
*
* @return the corresponding value
*/
public GroundedValue materialize() throws XPathException {
if (state == ALL_READ) {
return new SequenceExtent(reservoir);
} else if (state == EMPTY) {
return EmptySequence.getInstance();
}
return new SequenceExtent(iterate());
}
/**
* Get properties of this iterator, as a bit-significant integer.
*
* @return the properties of this iterator. This will be some combination of
* properties such as {@link #GROUNDED} and {@link #LAST_POSITION_FINDER}. It is always
* acceptable to return the value zero, indicating that there are no known special properties.
*/
public int getProperties() {
if (state == EMPTY || state == ALL_READ) {
return GROUNDED | LAST_POSITION_FINDER;
} else {
return 0;
}
}
}
}
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is “Incompatible With Secondary Licenses”, as defined by the Mozilla Public License, v. 2.0.