java.lang.Object
com.presumo.jms.selector.Parser
- public final class Parser
- extends java.lang.Object
Access point to the filter functionality for the rest of the JMS
implementation. This class (along with every other class in this package)
is on the critical path for message throughput performance. Thus it is,
and must remain optimized.
Parser is a singleton instead of a series of static methods because I read
somewhere that instance methods are faster than static methods (never
personally verified this). The class is thread safe, but to prevent the
routing thread from having to obtain a lock for every evaluation, a thread
can obtain the lock once and call several evaluations before releasing
the lock.
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Constructor Summary |
protected |
Parser()
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| Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
onlyInstance
private static Parser onlyInstance
lockOwner
private java.lang.Thread lockOwner
logger
private static com.presumo.util.log.Logger logger
Parser
protected Parser()
getInstance
public static Parser getInstance()
obtainLock
public void obtainLock()
- Called to obtain the mutex lock for the current thread. ReleaseLock()
must be called by the same thread.
releaseLock
public void releaseLock()
- Called to release the mutex lock held for this parser instance
resetEvaluateOnce
public void resetEvaluateOnce()
- The evaluate() method stores information about its last evaluation. This
is combined with the fact that all logically equivelant JMS filters in
a JVM are represented by the same instance of JmsOperand represents a
signficant optimization. The filtering is used by ONLY the routing thread
for evaluation, and for every message the thread has to deliver this method
is called. Then for every filter the routing thread needs to check the
message against the evaluate() method is called. If any sql expressions
(or subexpressions!!) are duplicated in the filters, they will only be
evaluated once.
evaluate
public boolean evaluate(JmsOperand root,
javax.jms.Message msg)
- Must be used in conjunction with resetEvaluateOnce().
parseFilter
public JmsOperand parseFilter(java.lang.String filter)
throws javax.jms.InvalidSelectorException
- Parse the filter and return a JmsOperand representing the root
node of the filter's expression tree.
unparse
public java.lang.String unparse(JmsOperand root)
andTogether
public JmsOperand andTogether(JmsOperand lv,
JmsOperand rv)
- Logically and's together two trees.
The returned expression tree must be deleted.
orTogether
public JmsOperand orTogether(JmsOperand[] roots)
- Logically or's together the trees
The returned expression tree must be deleted
delete
public void delete(JmsOperand root)
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