org.apache.hadoop.util

Class PluginDispatcher<T extends org.apache.hadoop.util.ServicePlugin>

java.lang.Object

org.apache.hadoop.util.PluginDispatcher<T>

public class PluginDispatcher<T extends org.apache.hadoop.util.ServicePlugin>
extends Object

Provides convenience functions for dispatching calls through to plugins registered with a class. Classes that wish to provide plugin interfaces should use this class to load the plugin list from the Configuration and to dispatch calls to the loaded instances. Calls dispatched through this class are performed on a second thread so as to not block execution of the plugged service.

Field Summary

Fields

Modifier and Type	Field and Description
static org.apache.commons.logging.Log	LOG

Method Summary

Methods

Modifier and Type	Method and Description
static <X extends org.apache.hadoop.util.ServicePlugin> PluginDispatcher<X>	createFromConfiguration(Configuration conf, String key, Class<X> clazz) Load a PluginDispatcher from the given Configuration.
void	dispatchCall(SingleArgumentRunnable<T> callback) Dispatch a call to all active plugins.
void	dispatchStart(Object plugPoint) Dispatches the start(...) hook common to all ServicePlugins.
void	dispatchStop() Convenience function for dispatching the stop() hook common to all ServicePlugins.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

LOG

public static final org.apache.commons.logging.Log LOG

Method Detail

createFromConfiguration

public static <X extends org.apache.hadoop.util.ServicePlugin> PluginDispatcher<X> createFromConfiguration(Configuration conf,
                                                                                           String key,
                                                                                           Class<X> clazz)

Load a PluginDispatcher from the given Configuration. The start() callback will not be automatically called.

Parameters:

conf - the Configuration from which to load

key - the configuration key that lists class names to instantiate

clazz - the class or interface from which plugins must extend

dispatchCall

public void dispatchCall(SingleArgumentRunnable<T> callback)

Dispatch a call to all active plugins. Exceptions will be caught and logged at WARN level.

Parameters:

callback - a function which will run once for each plugin, with that plugin as the argument

dispatchStart

public void dispatchStart(Object plugPoint)

Dispatches the start(...) hook common to all ServicePlugins. This also automatically removes any plugin that throws an exception while attempting to start.

Parameters:

plugPoint - passed to ServicePlugin.start()

dispatchStop

public void dispatchStop()

Convenience function for dispatching the stop() hook common to all ServicePlugins.