net.sf.saxon.instruct
Class TraceInstruction

java.lang.Object
  |
  +--net.sf.saxon.instruct.Instruction
        |
        +--net.sf.saxon.instruct.ExprInstruction
              |
              +--net.sf.saxon.instruct.TraceInstruction
All Implemented Interfaces:
Expression, Instr, Locatable, java.io.Serializable, javax.xml.transform.SourceLocator

public class TraceInstruction
extends ExprInstruction

A run-time instruction which wraps a real instruction and traces its entry and exit to the TraceListener

See Also:
Serialized Form

Field Summary
 
Fields inherited from class net.sf.saxon.instruct.Instruction
children
 
Constructor Summary
TraceInstruction(Instruction child)
          Create a Trace instruction
 
Method Summary
 Expression analyze(StaticContext env)
          Perform static analysis of an expression and its subexpressions.
 void display(int level, NamePool pool)
          Diagnostic print of expression structure.
 Item evaluateItem(XPathContext context)
          Evaluate an expression as a single item.
 int getDependencies()
          Determine which aspects of the context the expression depends on.
 java.lang.String getInstructionName()
          Get the name of the instruction being traced
 java.lang.String getInstructionNamespace()
          Get the namespace URI of the instruction being traced
 int getLineNumber()
          Get the line number of the instruction being traced
 int getSpecialProperties()
          Get the static properties of this expression (other than its type).
 java.lang.String getSystemId()
          Get the system ID of the module in which this instruction is located
protected  void getXPathExpressions(java.util.List list)
          Get all the XPath expressions associated with this instruction (in XSLT terms, the expression present on attributes of the instruction, as distinct from the child instructions in a sequence construction)
 SequenceIterator iterate(XPathContext context)
          Return an Iterator to iterate over the values of a sequence.
 TailCall processLeavingTail(XPathContext context)
          Execute this instruction, with the possibility of returning tail calls if there are any.
protected  void promoteInst(PromotionOffer offer)
          Handle promotion offers, that is, non-local tree rewrites.
 void setProperty(java.lang.String name, java.lang.Object value)
          Set a property to be supplied to the TraceListener when this instruction is executed
 Expression simplify()
          Simplify an expression.
 
Methods inherited from class net.sf.saxon.instruct.ExprInstruction
effectiveBooleanValue, evaluateAsString, getSubExpressions, promote
 
Methods inherited from class net.sf.saxon.instruct.Instruction
assembleParams, assembleTunnelParams, displayChildren, dynamicError, dynamicError, getCardinality, getChildren, getColumnNumber, getExecutable, getItemType, getPublicId, getSourceLocator, process, processChildren, processChildrenLeavingTail, recoverableError, setChildren, setExecutable, setSourceLocation
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface net.sf.saxon.expr.Expression
getCardinality, getItemType
 

Constructor Detail

TraceInstruction

public TraceInstruction(Instruction child)
Create a Trace instruction

Parameters:
child - the "real" instruction to be traced
Method Detail

setProperty

public void setProperty(java.lang.String name,
                        java.lang.Object value)
Set a property to be supplied to the TraceListener when this instruction is executed

Parameters:
name - the name of the property
value - the value of the property

getSystemId

public java.lang.String getSystemId()
Get the system ID of the module in which this instruction is located

Specified by:
getSystemId in interface javax.xml.transform.SourceLocator
Overrides:
getSystemId in class Instruction
Returns:
the system ID (URI) of the module

getLineNumber

public int getLineNumber()
Get the line number of the instruction being traced

Specified by:
getLineNumber in interface javax.xml.transform.SourceLocator
Overrides:
getLineNumber in class Instruction
Returns:
the line number (-1 if not known)

getInstructionName

public java.lang.String getInstructionName()
Get the name of the instruction being traced

Specified by:
getInstructionName in class Instruction
Returns:
the instruction name

getInstructionNamespace

public java.lang.String getInstructionNamespace()
Get the namespace URI of the instruction being traced

Overrides:
getInstructionNamespace in class Instruction
Returns:
the namespace URI of the instruction being traced

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
                            throws javax.xml.transform.TransformerException
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 Instr
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:
javax.xml.transform.TransformerException

simplify

public Expression simplify()
                    throws XPathException
Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.

Specified by:
simplify in interface Expression
Overrides:
simplify in class ExprInstruction
Returns:
the simplified expression
Throws:
XPathException - if an error is discovered during expression rewriting

analyze

public Expression analyze(StaticContext env)
                   throws XPathException
Perform static analysis of an expression and its subexpressions.

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 will only be accurately known if they have been explicitly declared.

Specified by:
analyze in interface Expression
Overrides:
analyze in class ExprInstruction
Parameters:
env - the static context of the expression
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)

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.

Specified by:
getDependencies in interface Expression
Overrides:
getDependencies in class ExprInstruction
Returns:
a set of bit-significant flags identifying the dependencies of the expression

getSpecialProperties

public int getSpecialProperties()
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.

Specified by:
getSpecialProperties in interface Expression
Overrides:
getSpecialProperties in class ExprInstruction
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.

Specified by:
evaluateItem in interface Expression
Overrides:
evaluateItem in class ExprInstruction
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.

Specified by:
iterate in interface Expression
Overrides:
iterate in class ExprInstruction
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

promoteInst

protected void promoteInst(PromotionOffer offer)
                    throws XPathException
Handle promotion offers, that is, non-local tree rewrites.

Specified by:
promoteInst in class ExprInstruction
Parameters:
offer - The type of rewrite being offered
Throws:
XPathException

getXPathExpressions

protected void getXPathExpressions(java.util.List list)
Get all the XPath expressions associated with this instruction (in XSLT terms, the expression present on attributes of the instruction, as distinct from the child instructions in a sequence construction)

Specified by:
getXPathExpressions in class ExprInstruction
Parameters:
list - A list to be populated with the list of XPath expressions

display

public void display(int level,
                    NamePool pool)
Diagnostic print of expression structure. The expression is written to the System.err output stream

Parameters:
level - indentation level for this expression