https://issues.apache.org/bugzilla/show_bug.cgi?id=49742
Summary: NPE in EventListenerList (Concurrency)
Product: Batik
Version: 1.7
Platform: PC
OS/Version: Windows XP
Status: NEW
Severity: minor
Priority: P2
Component: SVG DOM
AssignedTo: [email protected]
ReportedBy: [email protected]
not repeatable, not clearly reproducable. bug occurs frequently in our Jemmy
application GUI tests.
java.lang.NullPointerException
at
org.apache.batik.dom.events.EventListenerList.removeListener(EventListenerList.java:88)
at
org.apache.batik.dom.events.EventSupport.removeEventListenerNS(EventSupport.java:180)
at
org.apache.batik.dom.AbstractNode.removeEventListenerNS(AbstractNode.java:991)
at
org.apache.batik.dom.svg.SVGOMDocument.removeCSSNavigableDocumentListener(SVGOMDocument.java:473)
at
org.apache.batik.css.engine.CSSEngine.removeEventListeners(CSSEngine.java:487)
at org.apache.batik.css.engine.CSSEngine.dispose(CSSEngine.java:516)
at
org.apache.batik.bridge.BridgeContext.removeDOMListeners(BridgeContext.java:1291)
at org.apache.batik.bridge.BridgeContext.dispose(BridgeContext.java:1444)
at
org.apache.batik.swing.svg.AbstractJSVGComponent.installSVGDocument(AbstractJSVGComponent.java:721)
at
org.apache.batik.swing.JSVGCanvas.installSVGDocument(JSVGCanvas.java:591)
at
org.apache.batik.swing.svg.AbstractJSVGComponent$2.run(AbstractJSVGComponent.java:679)
I guess it's because we do call AbstractJSVGComponent's setSVGDocument
frequently. I assume while one call of setSVGDocument still processes its
installSVGDocument, another thread also tries to remove listeners.
Code in EventListenerList, which causes NPE, is eht "else if" condition:
else if (head != null
&& (namespaceURI != null &&
namespaceURI.equals(head.namespaceURI)
|| namespaceURI == null && head.namespaceURI == null)
&& listener == head.listener) {
head = head.next;
}
The only reason for NPE that I can figure out is, that the member "head" in
thread A passes the "head != null" condition, then thread B already processes
head=head.next (what may set head = NULL), and then thread A resumes with
accessing head.namecpaceURI or head.listener -> NPE.
What about assigning head to a local variable before entering the IF condition;
and using the local variable for the conditions (and as source for assignment)?
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