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Troubleshooting

Troubleshooting

My Program is not running as fast as I would like.

In general an application should run as fast under the Wrapper as it does when running standalone. Here are a few places to start looking.

| Console Output

On some platforms, including Windows, sending large quantities of text to System.out or System.err will cause the program to slow down. This is because all of that output is being rendered to the screen in a graphics environment. This is actually the OS eating the CPU rather than the Wrapper or your application but the end result is the same.

To significantly reduce this effect, use a logging tool which will output to a file rather than to stdout. By doing so the output is never sent to the Wrapper or the user console.

Another option which is almost as good is to configure the Wrapper's console log level, using the wrapper.console.loglevel property, so that the output is only sent to the Wrapper's log file. Console output is disabled by default when running as an NT service and the console has not been enabled.

| Memory
Make sure that your system has plenty of memory for the JVM to run without doing any disk swapping. Because of the way Java manages memory. A very significant speed hit is common simply because Java is forced to do paging of large amounts of its memory as it attempted to perform garbage collection.

| Sun's Documentation
Another good place to look is the Performance Documentation for the Java HotSpot VM page on Sun's site. In addition, there was a very informative JDC Tech Tip talking about garbage collection issues.

I get an error about not being able to write a pid file when starting the Wrapper.

Strarting with version 3.0.5 of the Java Service Wrapper, the wrapper.pidfile property was implemented on the Windows platform. Previous versions of the Wrapper ignored this property when running under Windows. However, if the wrapper.conf file that you are using was created using a version of the Wrapper prior to 3.0.0 then you may have this property defined as a holdout from when you copied the file from the example wrapper.conf. This will lead to an error like the following:

    ERROR: Could not write pid file /var/run/testwrapper.pid: The
    system cannot find the path specified. (0x3)

To resolve this simply edit your wrapper.conf file and remove the wrapper.pidfile property.

I am getting a warning that the Wrapper can not load its native library. What do I do?

A few users have asked about the following message showing up in their wrapper.log file:

    WARNING - Unable to load native library 'wrapper' for class WrapperManager.
              System signals will not be handled correctly.

This message is being shown because the Java component of the Wrapper was unable to load its native libraries during initialization. If you look in your wrapper.conf file, you will see a property, `wrapper.java.library.path`. This is used to specify the directory that the Wrapper will look in to find its native library. (Wrapper.DLL on Windows, or libwrapper.so on Unix systems) You should place the library file in the specified directory or change the property to point to the directory where it is located.

As of version 2.2.9 this error message was improved. You will now see something like the following (Depending on your platform of course):

    WARNING - Unable to load native library 'wrapper' because the
              file 'Wrapper.DLL' could not be located in the following
              java.library.path:
                C:\SourceForge\wrapper\bin\..\lib
              Please see the documentation for the wrapper.java.library.path
              configuration property.
              System signals will not be handled correctly.

I am unable to install my application as a service under Windows 2000 or NT.

On Windows 2000 or NT, you will see the following error message if you attempt to install a service when logged in as a user without Administrator privileges.

    OpenSCManager failed - access denied.

Solution. Contact your system administrator and beg them to install the service for you. Easy if that is you.

My Application will not start. What can I do to narrow down the problem?

Output describing the problem should be displayed in the console as well as the configured log file. To get more detailed output, edit your wrapper.conf file and enable debugging by uncommenting the wrapper.debug property. This will display very detailed output at every step in the process of launching and monitoring your application.

If your application works when not using the Wrapper, but fails with the Wrapper, then it is very likely that there is a problem in the way you set up your wrapper.conf file. Please look closely at the command used to launch java, in the debug output. It is possible that there is a mistake in the classpath or something.

I am not getting any output in my configured log file.

It is possible that the Wrapper is not able to locate the specified wrapper configuration file, or it is not able to open the configured log file for some reason. In either case, the Wrapper will log output to a file called wrapper.log in the current working directory. The current working directory will most likely be the directory containing the binary. However, in some cases, when running as an NT service, the wrapper.log file may be placed in your WinNT\System32 directory.

My application is hanging while it is shutting down.

If you call System.exit() in your application then Wrapper will catch this and attempt to shutdown the application cleanly. If during the shutdown process, your application once again calls System.exit() then the call will block indefinitely causing your application to hang. There are also problems with calling the destroy() method on an AWT frame or window from within a shutdown hoot thread. Please take a look at the wrapper.disable_shutdown_hook property in the Configuration File Overview for details on how to avoid this problem.

My 1.2.x JVM crashes when I run my application with the Wrapper.

Most of the features of the Wrapper will work with 1.2.x JVMs so the JVM is included on the list of supported JVMs. However, the released version of the wrapper is built using a 1.4.x version of Java. 1.2.x versions of the JVM have problems with the generated jar and will crash with very low level JNI errors. This appears to be a bug in the 1.4.x versions of the compiler as it happens even if the "1.1" JVM target is specified when compiling the classes.

Here is an example of the errors that I have seen:

    A nonfatal internal JIT (3.10.107(x)) error 'chgTarg: Conditional' has occurred in :
      'org/tanukisoftware/wrapper/WrapperManager.stopCommon (II)V': Interpreting method.
      Please report this error in detail to http://java.sun.com/cgi-bin/bugreport.cgi

I get help from several people to be able to produce the releases for all of the various supported platforms and it is not really possible to force everyone to use old JDKs to build the Wrapper distributions.

If you are experiencing crash problems with 1.2.x JVMs and the Wrapper please try downloading a source distribution and building the wrapper.jar file using your 1.2.x JDK. This will fix the problem.

If you are running into this, please post a note to the wrapper-user mailing list. I am not sure how many people are still using 1.2.x JVMs. But if it is still fairly common, I may reconsider the above policy and look into what it will take to get the releases built using an older JVM.

My JVM is sometimes restarted when the system is heavily loaded.

Because the Wrapper is using a pinging mechanism to check on the health of the JVM, it is possible that the Wrapper will think that the JVM is hung when it isn't if another process is taking 100% of the CPU for longer than 30 seconds. This will result in an entry like the following in your log file, and the JVM being restarted:

    jvm 1    | 2001/12/01 12:23:23 | start()
    wrapper  | 2001/12/01 12:23:44 | Startup failed: Timed out waiting for signal from JVM.
    wrapper  | 2001/12/01 12:23:44 | Java Virtual Machine did not exit on request, terminated
    wrapper  | 2001/12/01 12:23:49 | Launching a JVM...
    jvm 2    | 2001/12/01 12:23:50 | Initializing...

The property `wrapper.ping.timeout=30` in `conf/wrapper.log` can be used to extend this timeout. But be aware that this will also lengthen the amount of time that your application will remain hung in the event of a real problem.

by Leif Mortenson

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