[JENKINS-43449] Ensure that the maven-event-spy is thread safe (#34)

* [JENKINS-43449] Ensure that the maven-event-spy is thread safe

maven-spy/pom.xml

@@ -94,6 +94,19 @@
     </dependencies>
     <build>
         <plugins>
+            <plugin>
+                <groupId>org.codehaus.mojo</groupId>
+                <artifactId>findbugs-maven-plugin</artifactId>
+                <version>3.0.4</version>
+                <executions>
+                    <execution>
+                        <phase>verify</phase>
+                        <goals>
+                            <goal>check</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
             <plugin>
                 <groupId>org.sonatype.plugins</groupId>
                 <artifactId>sisu-maven-plugin</artifactId>

maven-spy/src/main/java/org/jenkinsci/plugins/pipeline/maven/eventspy/reporter/FileMavenEventReporter.java

@@ -41,13 +41,18 @@
 import java.text.SimpleDateFormat;
 import java.util.Date;
 
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.ThreadSafe;
+
 /**
  * @author <a href="mailto:cleclerc@cloudbees.com">Cyrille Le Clerc</a>
  */
+@ThreadSafe
 public class FileMavenEventReporter implements MavenEventReporter {
     File outFile;
+    @GuardedBy("this")
     PrintWriter out;
-
+    @GuardedBy("this")
     XMLWriter xmlWriter;
 
     public FileMavenEventReporter() throws IOException {
@@ -77,20 +82,20 @@ public FileMavenEventReporter() throws IOException {
     }
 
     @Override
-    public void print(Object message) {
+    public synchronized void print(Object message) {
         XmlWriterUtil.writeComment(xmlWriter, new Timestamp(System.currentTimeMillis()) + " - " + message);
         XmlWriterUtil.writeLineBreak(xmlWriter);
     }
 
     @Override
-    public void print(Xpp3Dom element) {
+    public synchronized void print(Xpp3Dom element) {
         element.setAttribute("_time", new Timestamp(System.currentTimeMillis()).toString());
         Xpp3DomWriter.write(xmlWriter, element);
         XmlWriterUtil.writeLineBreak(xmlWriter);
     }
 
     @Override
-    public void close() {
+    public synchronized void close() {
         xmlWriter.endElement();
 
         out.close();

maven-spy/src/main/java/org/jenkinsci/plugins/pipeline/maven/eventspy/reporter/MavenEventReporter.java

@@ -24,15 +24,27 @@
 
 package org.jenkinsci.plugins.pipeline.maven.eventspy.reporter;
 
+import org.apache.maven.eventspy.EventSpy;
 import org.codehaus.plexus.util.xml.Xpp3Dom;
 
+import javax.annotation.concurrent.ThreadSafe;
+
 /**
+ * WARNING: implementations of {@link MavenEventReporter} MUST be thread safe.
+ *
  * @author <a href="mailto:cleclerc@cloudbees.com">Cyrille Le Clerc</a>
  */
+@ThreadSafe
 public interface MavenEventReporter {
     void print(Object message);
 
     void print(Xpp3Dom element);
 
+    /**
+     * Close the reporter at the end of the Maven execution.
+     * No call to {@link #print(Object)} or {@link #print(Xpp3Dom)} will be made after the invocation of this method.
+     *
+     * @see EventSpy#close()
+     */
     void close();
 }

maven-spy/src/main/java/org/jenkinsci/plugins/pipeline/maven/eventspy/reporter/OutputStreamEventReporter.java

@@ -37,12 +37,18 @@
 import java.nio.charset.StandardCharsets;
 import java.sql.Timestamp;
 
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.ThreadSafe;
+
 /**
  * @author <a href="mailto:cleclerc@cloudbees.com">Cyrille Le Clerc</a>
  */
+@ThreadSafe
 public class OutputStreamEventReporter implements MavenEventReporter {
 
+    @GuardedBy("this")
     final PrintWriter out;
+    @GuardedBy("this")
     final XMLWriter xmlWriter;
 
     public OutputStreamEventReporter(OutputStream out) {
@@ -61,7 +67,7 @@ public OutputStreamEventReporter(Writer out) {
     }
 
     @Override
-    public void print(Object message) {
+    public synchronized void print(Object message) {
         String comment = new Timestamp(System.currentTimeMillis()) + " - " + message;
         XmlWriterUtil.writeComment(xmlWriter, comment);
         XmlWriterUtil.writeLineBreak(xmlWriter);
@@ -70,15 +76,15 @@ public void print(Object message) {
     }
 
     @Override
-    public void print(Xpp3Dom element) {
+    public synchronized void print(Xpp3Dom element) {
         Xpp3DomWriter.write(xmlWriter, element);
         XmlWriterUtil.writeLineBreak(xmlWriter);
 
         out.flush();
     }
 
     @Override
-    public void close() {
+    public synchronized void close() {
         xmlWriter.endElement();
         out.flush();
     }