ensure MBean names are unique by using a timestamp

merging the ruby.runtime_number with a timestamp with milli granularity
for the MBean name

fixes #2582

Sponsored by Lookout Inc.

core/src/main/java/org/jruby/management/BeanManagerImpl.java

@@ -3,6 +3,9 @@
 import java.lang.management.ManagementFactory;
 import java.lang.reflect.Method;
 import java.security.AccessControlException;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+
 import javax.management.InstanceAlreadyExistsException;
 import javax.management.InstanceNotFoundException;
 import javax.management.MBeanRegistrationException;
@@ -19,13 +22,16 @@ public class BeanManagerImpl implements BeanManager {
 
     private static final Logger LOG = LoggerFactory.getLogger("BeanManagerImpl");
 
+    private static final SimpleDateFormat FORMAT = new SimpleDateFormat("yyyyMMddHHmmssSSS");
+
     public final String base;
 
     private final boolean managementEnabled;
 
     public BeanManagerImpl(Ruby ruby, boolean managementEnabled) {
         this.managementEnabled = managementEnabled;
-        this.base = "org.jruby:type=Runtime,name=" + ruby.getRuntimeNumber() + ",";
+        this.base = "org.jruby:type=Runtime,name=" + FORMAT.format(new Date()) +
+                ruby.getRuntimeNumber() + ",";
     }
 
     public void register(JITCompilerMBean jitCompiler) {

core/src/test/java/org/jruby/management/ManagementBeanTest.java

@@ -0,0 +1,47 @@
+package org.jruby.management;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.TreeSet;
+
+import org.jruby.embed.LocalContextScope;
+import org.jruby.embed.ScriptingContainer;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class ManagementBeanTest {
+
+    @Test
+    public void testUniquenessOfBeanNames() throws Exception {
+        System.setProperty("jruby.management.enabled", "true");
+        final Collection<String> result = new TreeSet<String>();
+        // if concurrent runtime do produce unique names we are good
+        // see https://github.com/jruby/jruby/issues/2582
+        int number = java.lang.Runtime.getRuntime().availableProcessors();
+        Thread[] threads = new Thread[number];
+        for( int i = 0; i < number; i++) {
+            threads[i] = new Thread(new Runnable(){
+                public void run() {
+                    try {
+                        Thread.sleep(1);
+                    } catch (InterruptedException e) {
+                    }
+                    ScriptingContainer instance = new ScriptingContainer(LocalContextScope.SINGLETHREAD);
+                    String[] names = instance.runScriptlet( "mbs = java.lang.management.ManagementFactory.getPlatformMBeanServer;"
+                        + "h = mbs.queryNames( nil, nil);"
+                        + "hh = h.select { |a| a.to_s.start_with?( 'org.jruby:type=Runtime' ) };"
+                        + "hh.collect { |a| a.to_s }.join( '_' )" ).toString().split("_");
+                    synchronized(result){
+                        result.addAll(Arrays.asList(names));
+                    }
+                    instance.terminate();
+                }
+            });
+            threads[i].start();
+        }
+        for( int i = 0; i < number; i++) {
+            threads[i].join();
+        }
+        Assert.assertEquals( number * 5, result.size() );
+    }
+}