Detect listener attempts to access System.out/System.err and

terminate with a build exception before entering an infinte loop


PR:	14863


git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@274103 13f79535-47bb-0310-9956-ffa450edef68

docs/manual/develop.html

@@ -336,6 +336,14 @@ If you wish to attach a listener from the command line you may use the
 <p>will run Ant with a listener that generates an XML representation of the build progress. This
 listener is included with Ant, as is the default listener, which generates the logging to standard output.</p>
 
+<p><b>Note: </b>A listener must not access System.out and System.err directly since ouput on 
+these streams is redirected by Ant's core to the build event system. Accessing these 
+streams can cause an infinite loop in Ant. Depending on the version of Ant, this will
+either cause the build to terminate or the Java VM to run out of Stack space. A logger, also, may 
+not access System.out and System.err directly. It must use the streams with which it has
+been configured.
+</p>
+
 <hr>
 <h2><a name="integration">Source code integration</a></h2>
 

src/main/org/apache/tools/ant/Project.java

@@ -253,6 +253,11 @@ public class Project {
     /** Instance of a utility class to use for file operations. */
     private FileUtils fileUtils;
 
+    /** 
+     * Flag which catches Listeners which try to use System.out or System.err 
+     */
+    private boolean loggingMessage = false;
+    
     /**
      * Creates a new Ant project.
      */
@@ -2055,9 +2060,18 @@ public class Project {
                                         int priority) {
         event.setMessage(message, priority);
         Vector listeners = getBuildListeners();
-        for (int i = 0; i < listeners.size(); i++) {
-            BuildListener listener = (BuildListener) listeners.elementAt(i);
-            listener.messageLogged(event);
+        synchronized(this) {
+            if (loggingMessage) {
+                throw new BuildException("Listener attempted to access " 
+                    + (priority == MSG_ERR ? "System.err" : "System.out") 
+                    + " - infinite loop terminated");
+            }
+            loggingMessage = true;                
+            for (int i = 0; i < listeners.size(); i++) {
+                BuildListener listener = (BuildListener) listeners.elementAt(i);
+                listener.messageLogged(event);
+            }
+            loggingMessage = false;
         }
     }