pmd: fix #1037 Facing a showstopper issue in PMD Report Class

* wrapping the report listeners in a thread safe (synchronized) class
 * overtaking the listeners for each thread / report

pmd/etc/changelog.txt

@@ -1,6 +1,7 @@
 ???? ??, 2012 - 5.0.2:
 
 Fixed bug 1026: PMD doesn't handle 'value =' in SuppressWarnings annotation
+Fixed bug 1037: Facing a showstopper issue in PMD Report Class (report listeners)
 Fixed bug 1043: node.getEndLine() always returns 0 (ECMAscript)
 Fixed bug 1044: Unknown option: -excludemarker
 Fixed bug 1047: False Positive in 'for' loops for LocalVariableCouldBeFinal in 5.0.1

pmd/src/main/java/net/sourceforge/pmd/Report.java

@@ -22,15 +22,18 @@ import net.sourceforge.pmd.util.StringUtil;
 
 public class Report {
 
-	public static Report createReport(RuleContext ctx, String fileName) {
-		
-		Report report = new Report();
-		ctx.setReport(report);
-		ctx.setSourceCodeFilename(fileName);
-		ctx.setSourceCodeFile(new File(fileName));
-		return report;
-	}	
-	
+    public static Report createReport(RuleContext ctx, String fileName) {
+	Report report = new Report();
+
+	// overtake the listener
+	report.addSynchronizedListeners(ctx.getReport().getSynchronizedListeners());
+
+	ctx.setReport(report);
+	ctx.setSourceCodeFilename(fileName);
+	ctx.setSourceCodeFile(new File(fileName));
+	return report;
+    }
+
 	public static class ReadableDuration {
         private final long duration;
 
@@ -112,7 +115,7 @@ public class Report {
     // Note that this and the above data structure are both being maintained for a bit
     private final List<RuleViolation> violations = new ArrayList<RuleViolation>();
     private final Set<Metric> metrics = new HashSet<Metric>();
-    private final List<ReportListener> listeners = new ArrayList<ReportListener>();
+    private final List<SynchronizedReportListener> listeners = new ArrayList<SynchronizedReportListener>();
     private List<ProcessingError> errors;
     private List<RuleConfigurationError> configErrors;
     private Map<Integer, String> linesToSuppress = new HashMap<Integer, String>();
@@ -164,7 +167,7 @@ public class Report {
     }
 
     public void addListener(ReportListener listener) {
-        listeners.add(listener);
+        listeners.add(new SynchronizedReportListener(listener));
     }
 
     public List<SuppressedViolation> getSuppressedRuleViolations() {
@@ -266,13 +269,13 @@ public class Report {
     }
 
     public Iterator<ProcessingError> errors() {
-        return errors == null ? EmptyIterator.instance : errors.iterator();
+        return errors == null ? EmptyIterator.<ProcessingError> instance() : errors.iterator();
     }
 
     public Iterator<RuleConfigurationError> configErrors() {
-        return configErrors == null ? EmptyIterator.instance : errors.iterator();
+        return configErrors == null ? EmptyIterator.<RuleConfigurationError> instance() : configErrors.iterator();
     }
-    
+
     public int treeSize() {
         return violationTree.size();
     }
@@ -292,4 +295,12 @@ public class Report {
     public long getElapsedTimeInMillis() {
         return end - start;
     }
+
+    public List<SynchronizedReportListener> getSynchronizedListeners() {
+	return listeners;
+    }
+
+    public void addSynchronizedListeners(List<SynchronizedReportListener> synchronizedListeners) {
+	listeners.addAll(synchronizedListeners);
+    }
 }

pmd/src/main/java/net/sourceforge/pmd/RuleContext.java

@@ -42,10 +42,11 @@ public class RuleContext {
     }
 
     /**
-     * Constructor which shares attributes with the given RuleContext.
+     * Constructor which shares attributes and report listeners with the given RuleContext.
      */
     public RuleContext(RuleContext ruleContext) {
 	this.attributes = ruleContext.attributes;
+	this.report.addSynchronizedListeners(ruleContext.getReport().getSynchronizedListeners());
     }
 
     /**

pmd/src/main/java/net/sourceforge/pmd/SynchronizedReportListener.java

@@ -0,0 +1,27 @@
+/**
+ * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
+ */
+package net.sourceforge.pmd;
+
+import net.sourceforge.pmd.stat.Metric;
+
+/**
+ * Wraps a report listener in order to synchronize calls to it.
+ */
+public final class SynchronizedReportListener implements ReportListener {
+
+    private final ReportListener wrapped;
+    
+    public SynchronizedReportListener(ReportListener listener) {
+	this.wrapped = listener;
+    }
+    
+    public synchronized void ruleViolationAdded(RuleViolation ruleViolation) {
+	wrapped.ruleViolationAdded(ruleViolation);
+    }
+
+    public synchronized void metricAdded(Metric metric) {
+	wrapped.metricAdded(metric);
+    }
+
+}

pmd/src/main/java/net/sourceforge/pmd/util/EmptyIterator.java

@@ -1,3 +1,6 @@
+/**
+ * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
+ */
 package net.sourceforge.pmd.util;
 
 import java.util.Iterator;
@@ -9,10 +12,15 @@ import java.util.Iterator;
  *
  * @param <T>
  */
-@SuppressWarnings("rawtypes")
 public class EmptyIterator<T extends Object> implements Iterator<T> {
 
+    	@SuppressWarnings("rawtypes")
 	public static final Iterator instance = new EmptyIterator();
+    	
+    	@SuppressWarnings("unchecked")
+	public static final <T extends Object> Iterator<T> instance() {
+    	    return instance;
+    	}
 	
 	private EmptyIterator() {}
 	
@@ -23,4 +31,4 @@ public class EmptyIterator<T extends Object> implements Iterator<T> {
 	public void remove() {	
 		throw new UnsupportedOperationException();
 	}
-};
+}