net.sf.saxon.expr.instruct

Class TraceExpression

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.instruct.Instruction

net.sf.saxon.expr.instruct.TraceExpression

All Implemented Interfaces:

SourceLocator, TailCallReturner, IdentityComparable, InstructionInfo

public class TraceExpression
extends Instruction
implements InstructionInfo

A wrapper expression used to trace expressions in XPath and XQuery.

Field Summary

Fields inherited from class net.sf.saxon.expr.Expression

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, WATCH_METHOD

Constructor Summary

Constructors

Constructor and Description
TraceExpression(Expression child) Create a trace expression that traces execution of a given child expression

Method Summary

Methods

Modifier and Type	Method and Description
void	checkForUpdatingSubexpressions() Check to ensure that this expression does not contain any inappropriate updating subexpressions.
int	computeDependencies() Get the static properties of this expression (other than its type).
Expression	copy() Copy an expression.
boolean	createsNewNodes() Determine whether this instruction creates new nodes.
Item	evaluateItem(XPathContext context) Evaluate an expression as a single item.
void	evaluatePendingUpdates(XPathContext context, PendingUpdateList pul) Evaluate an updating expression, adding the results to a Pending Update List.
void	explain(ExpressionPresenter out) Diagnostic print of expression structure.
int	getCardinality() Determine the static cardinality of the expression.
Expression	getChildExpression()
int	getConstructType() Get the construct type.
int	getDependencies() Determine which aspects of the context the expression depends on.
ExpressionCompiler	getExpressionCompiler() Return the compiler of the Trace expression
int	getImplementationMethod() An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
InstructionInfo	getInstructionInfo() Get the InstructionInfo details about the construct.
int	getInstructionNameCode() Get the namecode of the instruction for use in diagnostics
ItemType	getItemType() Get the item type of the items returned by evaluating this instruction
NamespaceResolver	getNamespaceResolver() Get the namespace resolver to supply the namespace context of the instruction that is being traced
StructuredQName	getObjectName() Get a name identifying the object of the expression, for example a function name, template name, variable name, key name, element name, etc.
Iterator<String>	getProperties() Get an iterator over all the properties available.
Object	getProperty(String name) Get a named property of the instruction/expression
boolean	isUpdatingExpression() Determine whether this is an updating expression as defined in the XQuery update specification
boolean	isVacuousExpression() Determine whether this is a vacuous expression as defined in the XQuery update specification
SequenceIterator	iterate(XPathContext context) Return an Iterator to iterate over the values of a sequence.
Iterable<Operand>	operands() Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression.
Expression	optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) Perform optimisation of an expression and its subexpressions.
TailCall	processLeavingTail(XPathContext context) Execute this instruction, with the possibility of returning tail calls if there are any.
Expression	promote(PromotionOffer offer, Expression parent) Offer promotion for this subexpression.
boolean	replaceOperand(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
void	setConstructType(int type) Set the type of construct.
void	setNamespaceResolver(NamespaceResolver resolver) Set the namespace context for the instruction being traced.
void	setObjectName(StructuredQName qName) Set a name identifying the object of the expression, for example a function name, template name, variable name, key name, element name, etc.
void	setProperty(String name, Object value) Set a named property of the instruction/expression
Expression	typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Perform type checking of an expression and its subexpressions.

Methods inherited from class net.sf.saxon.expr.instruct.Instruction

assembleParams, assembleTunnelParams, computeCardinality, computeSpecialProperties, dynamicError, evaluateAsString, getExpressionName, getInstructionName, getIteratorFromProcessMethod, getSourceLocator, isXSLT, process, promoteInst, toStreamingPattern

Methods inherited from class net.sf.saxon.expr.Expression

addToPathMap, adoptChildExpression, checkPermittedContents, clearStreamabilityData, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, explain, getColumnNumber, getConfiguration, getContainer, getEvaluationMethod, getHostLanguage, getIntegerBounds, getIntrinsicDependencies, getLineNumber, getLocationId, getPosture, getPublicId, getSlotsUsed, getSpecialProperties, getStreamability, getStreamingAdjunct, getSweep, getSystemId, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isIdentical, isSubtreeExpression, iterateEvents, makeStreamingAdjunct, markTailFunctionCalls, operandList, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, setPostureAndSweep, simplify, staticTypeCheck, suppressValidation, toPattern, toShortString, toString, typeError, unordered

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface net.sf.saxon.trace.InstructionInfo

getLineNumber, getSystemId

Methods inherited from interface javax.xml.transform.SourceLocator

getColumnNumber, getPublicId

Constructor Detail

TraceExpression

public TraceExpression(Expression child)

Create a trace expression that traces execution of a given child expression

Parameters:

child - the expression to be traced. This will be available to the TraceListener as the value of the "expression" property of the InstructionInfo.

Method Detail

setConstructType

public void setConstructType(int type)

Set the type of construct. This will generally be a constant in class Location

Parameters:

type - an integer code for the type of construct being traced

getConstructType

public int getConstructType()

Get the construct type. This will generally be a constant in class Location

Specified by:

getConstructType in interface InstructionInfo

Overrides:

getConstructType in class Instruction

Returns:

the type of expression, as enumerated in class Location

setNamespaceResolver

public void setNamespaceResolver(NamespaceResolver resolver)

Set the namespace context for the instruction being traced. This is needed if the tracelistener wants to evaluate XPath expressions in the context of the current instruction

Parameters:

resolver - The namespace resolver, or null if none is needed

getNamespaceResolver

public NamespaceResolver getNamespaceResolver()

Get the namespace resolver to supply the namespace context of the instruction that is being traced

Returns:

the namespace resolver, or null if none is in use

setObjectName

public void setObjectName(StructuredQName qName)

Set a name identifying the object of the expression, for example a function name, template name, variable name, key name, element name, etc. This is used only where the name is known statically.

Parameters:

qName - the name of the object, or null if not applicable

getObjectName

public StructuredQName getObjectName()

Get a name identifying the object of the expression, for example a function name, template name, variable name, key name, element name, etc. This is used only where the name is known statically.

Specified by:

getObjectName in interface InstructionInfo

Overrides:

getObjectName in class Expression

Returns:

the name of the object, or null if not applicable

setProperty

public void setProperty(String name,
               Object value)

Set a named property of the instruction/expression

Parameters:

name - the name of the property

value - the value of the property

getProperty

public Object getProperty(String name)

Get a named property of the instruction/expression

Specified by:

getProperty in interface InstructionInfo

Overrides:

getProperty in class Expression

Parameters:

name - the name of the property

Returns:

the value of the property

getProperties

public Iterator<String> getProperties()

Get an iterator over all the properties available. The values returned by the iterator will be of type String, and each string can be supplied as input to the getProperty() method to retrieve the value of the property.

Specified by:

getProperties in interface InstructionInfo

Overrides:

getProperties in class Expression

Returns:

an iterator over the properties.

getInstructionInfo

public InstructionInfo getInstructionInfo()

Get the InstructionInfo details about the construct. This is to satisfy the InstructionInfoProvider interface.

Returns:

the instruction details

copy

public Expression copy()

Description copied from class: Expression

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Returns:

the copy of the original expression

isUpdatingExpression

public boolean isUpdatingExpression()

Determine whether this is an updating expression as defined in the XQuery update specification

Overrides:

isUpdatingExpression in class Expression

Returns:

true if this is an updating expression

isVacuousExpression

public boolean isVacuousExpression()

Determine whether this is a vacuous expression as defined in the XQuery update specification

Overrides:

isVacuousExpression in class Expression

Returns:

true if this expression is vacuous

checkForUpdatingSubexpressions

public void checkForUpdatingSubexpressions()
                                    throws XPathException

Check to ensure that this expression does not contain any inappropriate updating subexpressions. This check is overridden for those expressions that permit updating subexpressions.

Overrides:

checkForUpdatingSubexpressions in class Expression

Throws:

XPathException - if the expression has a non-permitted updating subexpression

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                   ContextItemStaticInfo contextInfo)
                     throws XPathException

Description copied from class: Expression

Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.

This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.

If the implementation returns a value other than "this", then it is required to ensure that the location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.

Overrides:

typeCheck in class Expression

Parameters:

visitor - an expression visitor

contextInfo - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.

Returns:

the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations

Throws:

XPathException - if an error is discovered during this phase (typically a type error)

optimize

public Expression optimize(ExpressionVisitor visitor,
                  ContextItemStaticInfo contextItemType)
                    throws XPathException

Description copied from class: Expression

Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.

Overrides:

optimize in class Expression

Parameters:

visitor - an expression visitor

contextItemType - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to Type.ITEM_TYPE

Returns:

the original expression, rewritten if appropriate to optimize execution

Throws:

XPathException - if an error is discovered during this phase (typically a type error)

getImplementationMethod

public int getImplementationMethod()

Description copied from class: Instruction

An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is prefered. For instructions this is the process() method.

Overrides:

getImplementationMethod in class Instruction

Returns:

the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

promote

public Expression promote(PromotionOffer offer,
                 Expression parent)
                   throws XPathException

Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. This method is always called at compile time.

Overrides:

promote in class Instruction

Parameters:

offer - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression

parent - the parent of the subexpression

Returns:

if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression

Throws:

XPathException - if any error is detected

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
                            throws XPathException

Execute this instruction, with the possibility of returning tail calls if there are any. This outputs the trace information via the registered TraceListener, and invokes the instruction being traced.

Specified by:

processLeavingTail in interface TailCallReturner

Specified by:

processLeavingTail in class Instruction

Parameters:

context - the dynamic execution context

Returns:

either null, or a tail call that the caller must invoke on return

Throws:

XPathException

getItemType

public ItemType getItemType()

Get the item type of the items returned by evaluating this instruction

Overrides:

getItemType in class Instruction

Returns:

the static item type of the instruction

getCardinality

public int getCardinality()

Determine the static cardinality of the expression. This establishes how many items there will be in the result of the expression, at compile time (i.e., without actually evaluating the result.

Overrides:

getCardinality in class Expression

Returns:

one of the values Cardinality.ONE_OR_MORE, Cardinality.ZERO_OR_MORE, Cardinality.EXACTLY_ONE, Cardinality.ZERO_OR_ONE, Cardinality.EMPTY. This default implementation returns ZERO_OR_MORE (which effectively gives no information).

getDependencies

public int getDependencies()

Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as StaticProperty.DEPENDS_ON_CONTEXT_ITEM and StaticProperty.DEPENDS_ON_CURRENT_ITEM. The default implementation combines the intrinsic dependencies of this expression with the dependencies of the subexpressions, computed recursively. This is overridden for expressions such as FilterExpression where a subexpression's dependencies are not necessarily inherited by the parent expression.

Overrides:

getDependencies in class Expression

Returns:

a set of bit-significant flags identifying the dependencies of the expression

createsNewNodes

public final boolean createsNewNodes()

Determine whether this instruction creates new nodes.

Overrides:

createsNewNodes in class Instruction

Returns:

true if the instruction creates new nodes (or if it can't be proved that it doesn't)

computeDependencies

public int computeDependencies()

Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.

Overrides:

computeDependencies in class Expression

Returns:

a set of flags indicating static properties of this expression

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.

Overrides:

evaluateItem in class Instruction

Parameters:

context - The context in which the expression is to be evaluated

Returns:

the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence

Throws:

XPathException - if any dynamic error occurs evaluating the expression

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.

Overrides:

iterate in class Instruction

Parameters:

context - supplies the context for evaluation

Returns:

a SequenceIterator that can be used to iterate over the result of the expression

Throws:

XPathException - if any dynamic error occurs evaluating the expression

operands

public Iterable<Operand> operands()

Description copied from class: Expression

Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression. Default implementation works off the results of iterateSubExpressions()

If the expression is a Callable, then it is required that the order of the operands returned by this function is the same as the order of arguments supplied to the corresponding call() method.

Overrides:

operands in class Expression

Returns:

an iterator containing the sub-expressions of this expression

replaceOperand

public boolean replaceOperand(Expression original,
                     Expression replacement)

Replace one subexpression by a replacement subexpression

Overrides:

replaceOperand in class Expression

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

getChildExpression

public Expression getChildExpression()

getInstructionNameCode

public int getInstructionNameCode()

Description copied from class: Instruction

Get the namecode of the instruction for use in diagnostics

Overrides:

getInstructionNameCode in class Instruction

Returns:

a code identifying the instruction: typically but not always the fingerprint of a name in the XSLT namespace

explain

public void explain(ExpressionPresenter out)

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:

explain in class Expression

Parameters:

out - the expression presenter used to display the structure

evaluatePendingUpdates

public void evaluatePendingUpdates(XPathContext context,
                          PendingUpdateList pul)
                            throws XPathException

Evaluate an updating expression, adding the results to a Pending Update List. The default implementation of this method, which is used for non-updating expressions, throws an UnsupportedOperationException

Overrides:

evaluatePendingUpdates in class Expression

Parameters:

context - the XPath dynamic evaluation context

pul - the pending update list to which the results should be written

Throws:

XPathException - if evaluation fails

getExpressionCompiler

public ExpressionCompiler getExpressionCompiler()

Return the compiler of the Trace expression

Overrides:

getExpressionCompiler in class Expression

Returns:

the relevant ExpressionCompiler