improving error diagnostics

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@7241 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/util/DoubleLaunchChecker.java

@@ -13,6 +13,8 @@ import java.io.File;
 import java.io.IOException;
 import java.util.Random;
 import java.util.logging.Logger;
+import java.util.logging.Level;
+import java.lang.management.ManagementFactory;
 
 /**
  * Makes sure that no other Hudson uses our <tt>HUDSON_HOME</tt> directory,
@@ -52,6 +54,12 @@ public class DoubleLaunchChecker {
 
     public final File home;
 
+    /**
+     * ID string of the other Hudson that we are colliding with. 
+     * Can be null.
+     */
+    private String collidingId;
+
     public DoubleLaunchChecker() {
         home = Hudson.getInstance().getRootDir();
     }
@@ -61,6 +69,11 @@ public class DoubleLaunchChecker {
 
         long t = timestampFile.lastModified();
         if(t!=0 && lastWriteTime!=0 && t!=lastWriteTime && !ignore) {
+            try {
+                collidingId = FileUtils.readFileToString(timestampFile);
+            } catch (IOException e) {
+                LOGGER.log(Level.SEVERE, "Failed to read collision file", e);
+            }
             // we noticed that someone else have updated this file.
             // switch GUI to display this error.
             Hudson.getInstance().servletContext.setAttribute("app",this);
@@ -69,7 +82,7 @@ public class DoubleLaunchChecker {
         }
 
         try {
-            FileUtils.writeStringToFile(timestampFile,"This file is used to make sure only one Hudson instance uses this directory");
+            FileUtils.writeStringToFile(timestampFile, getId());
             lastWriteTime = timestampFile.lastModified();
         } catch (IOException e) {
             // if failed to write, err on the safe side and assume things are OK.
@@ -79,6 +92,20 @@ public class DoubleLaunchChecker {
         schedule();
     }
 
+    /**
+     * Figures out a string that identifies this instance of Hudson.
+     */
+    public String getId() {
+        // FIXME: is there any way for us to obtain a servlet context path, so that
+        // we can help people distinguish two webapps running in the same container?
+
+        return Hudson.getInstance().hashCode()+" at "+ManagementFactory.getRuntimeMXBean().getName();
+    }
+
+    public String getCollidingId() {
+        return collidingId;
+    }
+
     /**
      * Schedules the next execution.
      */
@@ -89,7 +116,7 @@ public class DoubleLaunchChecker {
             protected void doRun() {
                 execute();
             }
-        },(random.nextInt(30*MINUTE)+60*MINUTE));
+        },(random.nextInt(30)+60)*MINUTE);
     }
 
     /**

core/src/main/resources/hudson/util/DoubleLaunchChecker/index.jelly

@@ -9,6 +9,16 @@
       <p>
         ${%message(it.home)}
       </p>
+      <table>
+        <tr>
+          <td>${%This Hudson}:</td>
+          <td>${it.id}</td>
+        </tr>
+        <tr>
+          <td>${%Other Hudson}:</td>
+          <td>${it.collidingId}</td>
+        </tr>
+      </table>
       <div>
         <form action="${rootURL}/ignore">
           <f:submit value="Ignore this problem and keep using Hudson anyway" />