Category Archives: Java/Java EE

mongrel tomcat launcher not working on neon

Posted on by
2

Edit: The solution is here

I used to use sydeo to launch Tomcat and then switched to Mongrel which I’ve been using for a few years. I had trouble with Mongrel in Eclipse Neon.

Symptoms

  • Clicking Start – get pop up with “The chosen operation is not available” and “Plugin net.sf.mongrel.plugin was unable to load class net.sf.mongrel.actions.StartActionDelegate” in the Eclipse log
  • Clicking Restart – get pop up with “The chosen operation is not available” and “Plugin net.sf.mongrel.plugin was unable to load class net.sf.mongrel.actions.RestartActionDelegate” in the Eclipse log
  • Clicking Stop – get pop up with “The chosen operation is not available” and “Plugin net.sf.mongrel.plugin was unable to load class net.sf.mongrel.actions.StopActionDelegate” in the Eclipse log
  • Opening Mongrel in the Eclipse preferences – get “An error has occurred while creating this preference page” and “Unable to create the selected preference page. An error occurred while automatically activating bundle net.sf.mongrel.plugin (1288).” The full Eclipse message in the error log is at the bottom of this post.

Attempt at solving

I checked the update site from Marketplace (by pasting the update site into “install new software” into Eclipse) and saw that there is only one version of Mongrel available. So it isn’t that I’m not using the latest version. I also tried uninstalling Mongrel and re-installing it. Nope. (You can uninstall a plugin through Marketplace if you installed it that way). Nothing.

I also learned I’m not the only one with this problem.

Workaround

The workaround is to use the WTP (web tool plugin) that comes with Eclipse as described here. Not a big deal. I just like the single button approach. I had upgraded to Java 8 since I last used WTP so I immediately got “unable to start Tomcat” with this log message in the console:

java.lang.UnsupportedClassVersionError: com/javaranch/jforum/csrf/CsrfListener : Unsupported major.minor version 52.0 (unable to load class com.javaranch.jforum.csrf.CsrfListener)

It was immediately obvious to me that WTP was pointing to Java 7 since I successfully launched this project in Mars a few days ago. I clicked on “runtime” in the Tomcat profile and choose Java 8 from the pull down. This updated the classpath and then I was successful.

Full message in case curious

eclipse.buildId=4.6.0.I20160606-1100

java.version=1.8.0_45

java.vendor=Oracle Corporation

BootLoader constants: OS=macosx, ARCH=x86_64, WS=cocoa, NL=en_US

Framework arguments:  -product org.eclipse.epp.package.jee.product -product org.eclipse.epp.package.jee.product -product org.eclipse.epp.package.jee.product -keyring /Users/nyjeanne/.eclipse_keyring

Command-line arguments:  -os macosx -ws cocoa -arch x86_64 -product org.eclipse.epp.package.jee.product -product org.eclipse.epp.package.jee.product -data file:/Users/nyjeanne/Documents/workspace/ -product org.eclipse.epp.package.jee.product -keyring /Users/nyjeanne/.eclipse_keyring

org.eclipse.equinox.registry

Error

Fri Jun 24 10:48:29 EDT 2016

Unable to create the selected preference page.

java.lang.ClassNotFoundException: An error occurred while automatically activating bundle net.sf.mongrel.plugin (975).

at org.eclipse.osgi.internal.hooks.EclipseLazyStarter.postFindLocalClass(EclipseLazyStarter.java:116)

at org.eclipse.osgi.internal.loader.classpath.ClasspathManager.findLocalClass(ClasspathManager.java:529)

at org.eclipse.osgi.internal.loader.ModuleClassLoader.findLocalClass(ModuleClassLoader.java:325)

at org.eclipse.osgi.internal.loader.BundleLoader.findLocalClass(BundleLoader.java:334)

at org.eclipse.osgi.internal.loader.BundleLoader.findClassInternal(BundleLoader.java:411)

at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:361)

at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:353)

at org.eclipse.osgi.internal.loader.ModuleClassLoader.loadClass(ModuleClassLoader.java:161)

at java.lang.ClassLoader.loadClass(ClassLoader.java:357)

at org.eclipse.osgi.internal.framework.EquinoxBundle.loadClass(EquinoxBundle.java:564)

at org.eclipse.core.internal.registry.osgi.RegistryStrategyOSGI.createExecutableExtension(RegistryStrategyOSGI.java:174)

at org.eclipse.core.internal.registry.ExtensionRegistry.createExecutableExtension(ExtensionRegistry.java:905)

at org.eclipse.core.internal.registry.ConfigurationElement.createExecutableExtension(ConfigurationElement.java:243)

at org.eclipse.core.internal.registry.ConfigurationElementHandle.createExecutableExtension(ConfigurationElementHandle.java:55)

at org.eclipse.ui.internal.WorkbenchPlugin$1.run(WorkbenchPlugin.java:291)

at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)

at org.eclipse.ui.internal.WorkbenchPlugin.createExtension(WorkbenchPlugin.java:286)

at org.eclipse.ui.internal.PluginAction.createDelegate(PluginAction.java:122)

at org.eclipse.ui.internal.PluginAction.runWithEvent(PluginAction.java:219)

at org.eclipse.ui.internal.WWinPluginAction.runWithEvent(WWinPluginAction.java:228)

at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:565)

at org.eclipse.jface.action.ActionContributionItem.lambda$5(ActionContributionItem.java:436)

at org.eclipse.jface.action.ActionContributionItem$$Lambda$34/501727405.handleEvent(Unknown Source)

at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)

at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4248)

at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1501)

at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1524)

at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1509)

at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1313)

at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4072)

at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3698)

at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$4.run(PartRenderingEngine.java:1121)

at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)

at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1022)

at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:150)

at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:687)

at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)

at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:604)

at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:148)

at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:138)

at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)

at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)

at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)

at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:388)

at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:243)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

at java.lang.reflect.Method.invoke(Method.java:497)

at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:673)

at org.eclipse.equinox.launcher.Main.basicRun(Main.java:610)

at org.eclipse.equinox.launcher.Main.run(Main.java:1519)

Caused by: org.osgi.framework.BundleException: Error loading bundle activator.

at org.eclipse.osgi.internal.framework.BundleContextImpl.start(BundleContextImpl.java:716)

at org.eclipse.osgi.internal.framework.EquinoxBundle.startWorker0(EquinoxBundle.java:932)

at org.eclipse.osgi.internal.framework.EquinoxBundle$EquinoxModule.startWorker(EquinoxBundle.java:309)

at org.eclipse.osgi.container.Module.doStart(Module.java:581)

at org.eclipse.osgi.container.Module.start(Module.java:449)

at org.eclipse.osgi.framework.util.SecureAction.start(SecureAction.java:470)

at org.eclipse.osgi.internal.hooks.EclipseLazyStarter.postFindLocalClass(EclipseLazyStarter.java:107)

… 51 more

Caused by: java.lang.ClassNotFoundException: org.eclipse.core.internal.compatibility.PluginActivator cannot be found by net.sf.mongrel.plugin_1.0.0.201101221622

at org.eclipse.osgi.internal.loader.BundleLoader.findClassInternal(BundleLoader.java:448)

at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:361)

at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:353)

at org.eclipse.osgi.internal.framework.BundleContextImpl.loadBundleActivator(BundleContextImpl.java:757)

at org.eclipse.osgi.internal.framework.BundleContextImpl.start(BundleContextImpl.java:711)

… 57 more

performance engineer’s guide to hotspot JIT compilation – monica beckwith – qcon

Posted on by
Reply

For more QCon posts, see my live blog table of contents. This presentation is about the compiler and also the runtime.

Major pieces

  • Execution engine
    • Heap management/garbage collection
    • JIT compilation
  • Runtime
    • VM Class loading
    • Interpretter
    • Byte code verification,etc

Runtime goal – convert from bytecode to native code and do optimizations along the way

Compilation Techniques and Notes

  • Pre-compiled/ahead of time
  • profile guided – based on critical hotspots
  • Adaptive optimization (Java uses Profile guided and Adaptive optimization)
  • Identify root of compilation
  • replace method or on stack – depends on number of times through loop
  • Server compiler has a higher threshold than client compiler for the threshold at which you need optimizations
  • Tiered compilation – tier 1 is client compiler with no profiling info, tier 2 and 3 are client compiler with profiling info. Then comes server compiler
  • CodeCache order of magnitude larger when tiered compilation is enabled. If need more can use -XX:ReservedCodeCacheSize
  • Inlining – many different parameters when figuring out when to inline
  • Vectorization – SIMD (SIngle Instruction Multiple Data). Can generate stubs and benefit from caching size chunks. For SuperWord Level Parallelism, you need to unroll the loop, do analysis/pre-optimization, etc. Still in infancy with Hotspot.
  • Escape analysis – Want to see if object only is used in a compile method. Need entire graph to confirm not in a static field/returned from method/passed as parameter/etc. If really local, can optimize by storing in registers.
  • Objects are 8 byte aligned by default. Fields are aligned by type.
  • OOP (ordinary object pointer) is a managed pointer. The size can be changed to optimize.
  • Compressed Class Pointers – part of the Metaspace. Class data is outside of heap.

Deoptimization

  1. dependency issues
  2. class unloading/redefinition
  3. uncommon path
  4. profiled info isn’t useful for path [like with databases when db assumes something different than you want]

If curious about details

To get information about what compiler thinks/did:

  • PrintCompilation – ex: what level instructions were compiled at
  • PrintInlining – use -XX:+UnlockDiagonsticVMOptions

reactive programming for java developers – rossen stoyanchev – qcon

Posted on by
Reply

For more QCon posts, see my live blog table of contents.

General notes

  • Spring 5 has reactive features.
  • Maybe a third of the audience is doing something with reactive, a little more have read about it (that’s me) and a lot haven’t heard of it. Which is good given the title of this talk!
  • Moore’s law slowing down. No more free lunch from the hardware
  • Now apps more distributed/independent/cloudbased compared to 10 years ago
  • Now we expect latency
  • Thread now has to do more async things. Hit limits of scale. imperative logic more complicated.

Other approach

  • Async/non-blocking
  • Use very few threads. node.js has a single thread. Must be careful because blocking those few threads blocks the whole app
  • Reactive programming – think async. Not everything is a callback

Comparing styles

  • Imperative
    • call a method, get a result, do something with that result
  • Async
    • return a Future instead of a value. Don’t throw a checked exception because my happen in a different thread. They are asynchronous in that you can get a result later. But when you eventually call feature.get(), it throws different checked exceptions.
    • In Java 8, can return a CompletableFuture and call future.whenComplete((user, throwable) -> {})
    • If doing a findAll(), the future/completable future approach doesn’t give you a callback/return anything until all of them are ready. You can’t stream or could run out of memory.
    • Async results as stream – get one notification per data item and another for completion or error
  • Declarative
    • Focus on what, not how
    • Declare what should happen rather than focusing on callbacks
    • Java 8 stream API uses this style. It is meant for collections and pull based/usable once
    • Hot streams – latency sensitive streams, data need to be pushed for you
    • Cold streams – pull based

Reactive libraries

  • Stream like API
  • Can be used for hot/cold streams
  • Project Reactor – Similar to ReactiveX, easy to bridge to Java 8 streams. (ReactiveX is like XUnit – commonality for different languages)

Abstractions

  • Flux – sequence of 0 to n – equivalent of Java 8 stream – can convert to/from Java 8
  • Mono – sequence of 0 or 1 – can convert to/from CompletableFuture

Reactive streams spec

  • Back pressure – producers must not overwhelm consumers. Communicates if downstream isn’t ready for more items. Ex: a slow client like a mobile device isnt able to handle more data and server isn’t blocking
  • Small API – only 4 interfaces
  • Rules
  • Interoperability across reactive components so can compose chain

Java 9

  • Reactive streams included (the four interfaces)
    • Publisher
    • Subscriber
    • Subscription
    • Processor
  • Use a reactive library. Don’t implement the four interfaces yourself
  • subscribe() triggers the flow of data
  • “push” was missing until now. Want in JDK to have foundation
  • Classes
    • java.util.concurrent.Flow – the four interfaces
    • SubmissionPublisher – bridge to reactie streams
    • Tie-ins to CompletableFuture and Stream

Reactor

  • GA release scheduled for July
  • Currently called 2.5. Might changed to 3.0

Reactive Spring MVC

  • Apps annotate controllers even now.
  • Return a Flux type.
  • Spring MVC itself needs to change a lot – called Spring Web Reactive
  • The servlet API assumes blocking. There are async workarounds. Servlet 4.0 might support reactive spring integration, but probably just the basics. Using own bridge to Servlet 3.1 in meantime.
  • Can still use Jetty/Tomcat. They are non-blocking behind the scenes.
  • Don’t need servlet container. Can use Netty.
  • HandlerMapping – change to return a Mono so can be non-blocking
  • Focusing on REST/microservices scenarios

Other reactive efforts

  • MongoDB – reactive driver
  • Couchbase – reactive driver
  • Thymeleaf – split templates into chunks and throttle to respect backpressure