org.glassfish.admin.amx.util

Class FeatureAvailability

java.lang.Object

org.glassfish.admin.amx.util.FeatureAvailability

public final class FeatureAvailability
extends Object

Central registry of available features for fine-grained dependency enforcement in a threaded environment.

Providers of features can register the availability (initializated and ready-to-use) of a particular feature, upon which other code depends. See registerFeature(java.lang.String, java.lang.Object).

Code that requires an initialized and ready-to-use feature should call waitForFeature(java.lang.String, java.lang.String)--the calling thread will block until that feature is available.

Feature names are arbitrary and *should not* be defined as 'public static final String' in this class unless they are of general system interest. Features that are not of general interest can and should still be registered through this mechanism, but the names of those features and the associated data can be defined in a more appropriate place.

Provider Example

...provider runs in its own thread...
FeatureAvailability.registerFeature( FeatureAvailability.MBEAN_SERVER_FEATURE, mbeanServer );

Client Example
(arbitrary number of clients, multiple calls OK)

...client runs until feature is needed...
final MBeanServer mbeanServer = (MBeanServer)
FeatureAvailability.waitForFeature( FeatureAvailability.MBEAN_SERVER_FEATURE );

To see how long client code is blocking, set the DEBUG_ENABLED flag to true.

Field Summary

Fields

Modifier and Type	Field and Description
static String	AMX_CORE_READY_FEATURE feature stating that the AMX core is ready for use after having been started.
static String	AMX_LOADER_FEATURE feature stating that the AMX MBean Loader is available (but not AMX).
static String	AMX_READY_FEATURE feature stating that the AMX and all its subsystems are ready for use.

Method Summary

Modifier and Type	Method and Description
void	deRegisterFeatures()
static FeatureAvailability	getInstance()
void	registerFeature(String featureName, Object data) Register a named feature as being ready for use.
Object	waitForFeature(String featureName, String callerInfo) Block until the specified feature is available.

Methods inherited from class java.lang.Object

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

Field Detail

AMX_LOADER_FEATURE

public static final String AMX_LOADER_FEATURE

feature stating that the AMX MBean Loader is available (but not AMX). Data should not be used

See Also:

Constant Field Values

AMX_CORE_READY_FEATURE

public static final String AMX_CORE_READY_FEATURE

feature stating that the AMX core is ready for use after having been started. Data should not be used. Other AMX subystems might still be in the process of initializing

See Also:

Constant Field Values

AMX_READY_FEATURE

public static final String AMX_READY_FEATURE

feature stating that the AMX and all its subsystems are ready for use. Data is the ObjectName of the DomainRoot

See Also:

Constant Field Values

Method Detail

getInstance

public static FeatureAvailability getInstance()

registerFeature

public void registerFeature(String featureName,
                            Object data)

Register a named feature as being ready for use. The data value can be a dummy value, or can be something useful to the caller of waitForFeature().

Do not register a feature until its facilities are ready for use.

Features should generally be fine-grained, not coarse. For example, the AdminService is a coarsely-defined feature which initializes dozens of things; code that requires the presence of one of those things should arrange for a name feature for that. Examples of this include the MBeanServer, the AdminContext, com.sun.appserv:category=config MBeans, etc.

Parameters:

featureName - arbitrary name for the feature, to be used by clients in waitForFeature(java.lang.String, java.lang.String)

data - arbitrary data of possible interest to clients

waitForFeature

public Object waitForFeature(String featureName,
                             String callerInfo)

Block until the specified feature is available.

Parameters:

featureName - the name of the desired feature

callerInfo - arbitrary caller info for debugging purposes

deRegisterFeatures

public void deRegisterFeatures()