org.osgi.util.tracker.ServiceTracker Maven / Gradle / Ivy
/*
* Copyright (c) OSGi Alliance (2000, 2009). All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.osgi.util.tracker;
import java.security.AccessController;
import java.security.PrivilegedAction;
import org.osgi.framework.AllServiceListener;
import org.osgi.framework.BundleContext;
import org.osgi.framework.Constants;
import org.osgi.framework.Filter;
import org.osgi.framework.InvalidSyntaxException;
import org.osgi.framework.ServiceEvent;
import org.osgi.framework.ServiceListener;
import org.osgi.framework.ServiceReference;
import org.osgi.framework.Version;
/**
* The ServiceTracker class simplifies using services from the
* Framework's service registry.
*
* A ServiceTracker object is constructed with search criteria and
* a ServiceTrackerCustomizer object. A ServiceTracker
* can use a ServiceTrackerCustomizer to customize the service
* objects to be tracked. The ServiceTracker can then be opened to
* begin tracking all services in the Framework's service registry that match
* the specified search criteria. The ServiceTracker correctly
* handles all of the details of listening to ServiceEvents and
* getting and ungetting services.
*
* The getServiceReferences method can be called to get references
* to the services being tracked. The getService and
* getServices methods can be called to get the service objects for
* the tracked service.
*
* The ServiceTracker class is thread-safe. It does not call a
* ServiceTrackerCustomizer while holding any locks.
* ServiceTrackerCustomizer implementations must also be
* thread-safe.
*
* @ThreadSafe
* @version $Revision: 6386 $
*/
public class ServiceTracker implements ServiceTrackerCustomizer {
/* set this to true to compile in debug messages */
static final boolean DEBUG = false;
/**
* The Bundle Context used by this ServiceTracker.
*/
protected final BundleContext context;
/**
* The Filter used by this ServiceTracker which specifies the
* search criteria for the services to track.
*
* @since 1.1
*/
protected final Filter filter;
/**
* The ServiceTrackerCustomizer for this tracker.
*/
final ServiceTrackerCustomizer customizer;
/**
* Filter string for use when adding the ServiceListener. If this field is
* set, then certain optimizations can be taken since we don't have a user
* supplied filter.
*/
final String listenerFilter;
/**
* Class name to be tracked. If this field is set, then we are tracking by
* class name.
*/
private final String trackClass;
/**
* Reference to be tracked. If this field is set, then we are tracking a
* single ServiceReference.
*/
private final ServiceReference trackReference;
/**
* Tracked services: ServiceReference -> customized Object and
* ServiceListener object
*/
private volatile Tracked tracked;
/**
* Accessor method for the current Tracked object. This method is only
* intended to be used by the unsynchronized methods which do not modify the
* tracked field.
*
* @return The current Tracked object.
*/
private Tracked tracked() {
return tracked;
}
/**
* Cached ServiceReference for getServiceReference.
*
* This field is volatile since it is accessed by multiple threads.
*/
private volatile ServiceReference cachedReference;
/**
* Cached service object for getService.
*
* This field is volatile since it is accessed by multiple threads.
*/
private volatile Object cachedService;
/**
* org.osgi.framework package version which introduced
* {@link ServiceEvent#MODIFIED_ENDMATCH}
*/
private static final Version endMatchVersion = new Version(1, 5, 0);
/**
* Create a ServiceTracker on the specified
* ServiceReference.
*
*
* The service referenced by the specified ServiceReference
* will be tracked by this ServiceTracker.
*
* @param context The BundleContext against which the tracking
* is done.
* @param reference The ServiceReference for the service to be
* tracked.
* @param customizer The customizer object to call when services are added,
* modified, or removed in this ServiceTracker. If
* customizer is null, then this
* ServiceTracker will be used as the
* ServiceTrackerCustomizer and this
* ServiceTracker will call the
* ServiceTrackerCustomizer methods on itself.
*/
public ServiceTracker(final BundleContext context,
final ServiceReference reference,
final ServiceTrackerCustomizer customizer) {
this.context = context;
this.trackReference = reference;
this.trackClass = null;
this.customizer = (customizer == null) ? this : customizer;
this.listenerFilter = "(" + Constants.SERVICE_ID + "="
+ reference.getProperty(Constants.SERVICE_ID).toString() + ")";
try {
this.filter = context.createFilter(listenerFilter);
}
catch (InvalidSyntaxException e) {
/*
* we could only get this exception if the ServiceReference was
* invalid
*/
IllegalArgumentException iae = new IllegalArgumentException(
"unexpected InvalidSyntaxException: " + e.getMessage());
iae.initCause(e);
throw iae;
}
}
/**
* Create a ServiceTracker on the specified class name.
*
*
* Services registered under the specified class name will be tracked by
* this ServiceTracker.
*
* @param context The BundleContext against which the tracking
* is done.
* @param clazz The class name of the services to be tracked.
* @param customizer The customizer object to call when services are added,
* modified, or removed in this ServiceTracker. If
* customizer is null, then this
* ServiceTracker will be used as the
* ServiceTrackerCustomizer and this
* ServiceTracker will call the
* ServiceTrackerCustomizer methods on itself.
*/
public ServiceTracker(final BundleContext context, final String clazz,
final ServiceTrackerCustomizer customizer) {
this.context = context;
this.trackReference = null;
this.trackClass = clazz;
this.customizer = (customizer == null) ? this : customizer;
// we call clazz.toString to verify clazz is non-null!
this.listenerFilter = "(" + Constants.OBJECTCLASS + "="
+ clazz.toString() + ")";
try {
this.filter = context.createFilter(listenerFilter);
}
catch (InvalidSyntaxException e) {
/*
* we could only get this exception if the clazz argument was
* malformed
*/
IllegalArgumentException iae = new IllegalArgumentException(
"unexpected InvalidSyntaxException: " + e.getMessage());
iae.initCause(e);
throw iae;
}
}
/**
* Create a ServiceTracker on the specified Filter
* object.
*
*
* Services which match the specified Filter object will be
* tracked by this ServiceTracker.
*
* @param context The BundleContext against which the tracking
* is done.
* @param filter The Filter to select the services to be
* tracked.
* @param customizer The customizer object to call when services are added,
* modified, or removed in this ServiceTracker. If
* customizer is null, then this ServiceTracker will be
* used as the ServiceTrackerCustomizer and this
* ServiceTracker will call the
* ServiceTrackerCustomizer methods on itself.
* @since 1.1
*/
public ServiceTracker(final BundleContext context, final Filter filter,
final ServiceTrackerCustomizer customizer) {
this.context = context;
this.trackReference = null;
this.trackClass = null;
final Version frameworkVersion = (Version) AccessController
.doPrivileged(new PrivilegedAction() {
public Object run() {
String version = context
.getProperty(Constants.FRAMEWORK_VERSION);
return (version == null) ? Version.emptyVersion
: new Version(version);
}
});
final boolean endMatchSupported = (frameworkVersion
.compareTo(endMatchVersion) >= 0);
this.listenerFilter = endMatchSupported ? filter.toString() : null;
this.filter = filter;
this.customizer = (customizer == null) ? this : customizer;
if ((context == null) || (filter == null)) {
/*
* we throw a NPE here to be consistent with the other constructors
*/
throw new NullPointerException();
}
}
/**
* Open this ServiceTracker and begin tracking services.
*
*
* This implementation calls open(false).
*
* @throws java.lang.IllegalStateException If the BundleContext
* with which this ServiceTracker was created is no
* longer valid.
* @see #open(boolean)
*/
public void open() {
open(false);
}
/**
* Open this ServiceTracker and begin tracking services.
*
*
* Services which match the search criteria specified when this
* ServiceTracker was created are now tracked by this
* ServiceTracker.
*
* @param trackAllServices If true, then this
* ServiceTracker will track all matching services
* regardless of class loader accessibility. If false,
* then this ServiceTracker will only track matching
* services which are class loader accessible to the bundle whose
* BundleContext is used by this
* ServiceTracker.
* @throws java.lang.IllegalStateException If the BundleContext
* with which this ServiceTracker was created is no
* longer valid.
* @since 1.3
*/
public void open(boolean trackAllServices) {
final Tracked t;
synchronized (this) {
if (tracked != null) {
return;
}
if (DEBUG) {
System.out.println("ServiceTracker.open: " + filter);
}
t = trackAllServices ? new AllTracked() : new Tracked();
synchronized (t) {
try {
context.addServiceListener(t, listenerFilter);
ServiceReference[] references = null;
if (trackClass != null) {
references = getInitialReferences(trackAllServices,
trackClass, null);
}
else {
if (trackReference != null) {
if (trackReference.getBundle() != null) {
references = new ServiceReference[] {trackReference};
}
}
else { /* user supplied filter */
references = getInitialReferences(trackAllServices,
null,
(listenerFilter != null) ? listenerFilter
: filter.toString());
}
}
/* set tracked with the initial references */
t.setInitial(references);
}
catch (InvalidSyntaxException e) {
throw new RuntimeException(
"unexpected InvalidSyntaxException: "
+ e.getMessage(), e);
}
}
tracked = t;
}
/* Call tracked outside of synchronized region */
t.trackInitial(); /* process the initial references */
}
/**
* Returns the list of initial ServiceReferences that will be
* tracked by this ServiceTracker.
*
* @param trackAllServices If true, use
* getAllServiceReferences.
* @param className The class name with which the service was registered, or
* null for all services.
* @param filterString The filter criteria or null for all
* services.
* @return The list of initial ServiceReferences.
* @throws InvalidSyntaxException If the specified filterString has an
* invalid syntax.
*/
private ServiceReference[] getInitialReferences(boolean trackAllServices,
String className, String filterString)
throws InvalidSyntaxException {
if (trackAllServices) {
return context.getAllServiceReferences(className, filterString);
}
return context.getServiceReferences(className, filterString);
}
/**
* Close this ServiceTracker.
*
*
* This method should be called when this ServiceTracker should
* end the tracking of services.
*
*
* This implementation calls {@link #getServiceReferences()} to get the list
* of tracked services to remove.
*/
public void close() {
final Tracked outgoing;
final ServiceReference[] references;
synchronized (this) {
outgoing = tracked;
if (outgoing == null) {
return;
}
if (DEBUG) {
System.out.println("ServiceTracker.close: " + filter);
}
outgoing.close();
references = getServiceReferences();
tracked = null;
try {
context.removeServiceListener(outgoing);
}
catch (IllegalStateException e) {
/* In case the context was stopped. */
}
}
modified(); /* clear the cache */
synchronized (outgoing) {
outgoing.notifyAll(); /* wake up any waiters */
}
if (references != null) {
for (int i = 0; i < references.length; i++) {
outgoing.untrack(references[i], null);
}
}
if (DEBUG) {
if ((cachedReference == null) && (cachedService == null)) {
System.out
.println("ServiceTracker.close[cached cleared]: "
+ filter);
}
}
}
/**
* Default implementation of the
* ServiceTrackerCustomizer.addingService method.
*
*
* This method is only called when this ServiceTracker has been
* constructed with a null ServiceTrackerCustomizer argument.
*
*
* This implementation returns the result of calling getService
* on the BundleContext with which this
* ServiceTracker was created passing the specified
* ServiceReference.
*
* This method can be overridden in a subclass to customize the service
* object to be tracked for the service being added. In that case, take care
* not to rely on the default implementation of
* {@link #removedService(ServiceReference, Object) removedService} to unget
* the service.
*
* @param reference The reference to the service being added to this
* ServiceTracker.
* @return The service object to be tracked for the service added to this
* ServiceTracker.
* @see ServiceTrackerCustomizer#addingService(ServiceReference)
*/
public Object addingService(ServiceReference reference) {
return context.getService(reference);
}
/**
* Default implementation of the
* ServiceTrackerCustomizer.modifiedService method.
*
*
* This method is only called when this ServiceTracker has been
* constructed with a null ServiceTrackerCustomizer argument.
*
*
* This implementation does nothing.
*
* @param reference The reference to modified service.
* @param service The service object for the modified service.
* @see ServiceTrackerCustomizer#modifiedService(ServiceReference, Object)
*/
public void modifiedService(ServiceReference reference, Object service) {
/* do nothing */
}
/**
* Default implementation of the
* ServiceTrackerCustomizer.removedService method.
*
*
* This method is only called when this ServiceTracker has been
* constructed with a null ServiceTrackerCustomizer argument.
*
*
* This implementation calls ungetService, on the
* BundleContext with which this ServiceTracker
* was created, passing the specified ServiceReference.
*
* This method can be overridden in a subclass. If the default
* implementation of {@link #addingService(ServiceReference) addingService}
* method was used, this method must unget the service.
*
* @param reference The reference to removed service.
* @param service The service object for the removed service.
* @see ServiceTrackerCustomizer#removedService(ServiceReference, Object)
*/
public void removedService(ServiceReference reference, Object service) {
context.ungetService(reference);
}
/**
* Wait for at least one service to be tracked by this
* ServiceTracker. This method will also return when this
* ServiceTracker is closed.
*
*
* It is strongly recommended that waitForService is not used
* during the calling of the BundleActivator methods.
* BundleActivator methods are expected to complete in a short
* period of time.
*
*
* This implementation calls {@link #getService()} to determine if a service
* is being tracked.
*
* @param timeout The time interval in milliseconds to wait. If zero, the
* method will wait indefinitely.
* @return Returns the result of {@link #getService()}.
* @throws InterruptedException If another thread has interrupted the
* current thread.
* @throws IllegalArgumentException If the value of timeout is negative.
*/
public Object waitForService(long timeout) throws InterruptedException {
if (timeout < 0) {
throw new IllegalArgumentException("timeout value is negative");
}
Object object = getService();
while (object == null) {
final Tracked t = tracked();
if (t == null) { /* if ServiceTracker is not open */
return null;
}
synchronized (t) {
if (t.size() == 0) {
t.wait(timeout);
}
}
object = getService();
if (timeout > 0) {
return object;
}
}
return object;
}
/**
* Return an array of ServiceReferences for all services being
* tracked by this ServiceTracker.
*
* @return Array of ServiceReferences or null if
* no services are being tracked.
*/
public ServiceReference[] getServiceReferences() {
final Tracked t = tracked();
if (t == null) { /* if ServiceTracker is not open */
return null;
}
synchronized (t) {
int length = t.size();
if (length == 0) {
return null;
}
return (ServiceReference[]) t
.getTracked(new ServiceReference[length]);
}
}
/**
* Returns a ServiceReference for one of the services being
* tracked by this ServiceTracker.
*
*
* If multiple services are being tracked, the service with the highest
* ranking (as specified in its service.ranking property) is
* returned. If there is a tie in ranking, the service with the lowest
* service ID (as specified in its service.id property); that
* is, the service that was registered first is returned. This is the same
* algorithm used by BundleContext.getServiceReference.
*
*
* This implementation calls {@link #getServiceReferences()} to get the list
* of references for the tracked services.
*
* @return A ServiceReference or null if no
* services are being tracked.
* @since 1.1
*/
public ServiceReference getServiceReference() {
ServiceReference reference = cachedReference;
if (reference != null) {
if (DEBUG) {
System.out
.println("ServiceTracker.getServiceReference[cached]: "
+ filter);
}
return reference;
}
if (DEBUG) {
System.out.println("ServiceTracker.getServiceReference: " + filter);
}
ServiceReference[] references = getServiceReferences();
int length = (references == null) ? 0 : references.length;
if (length == 0) { /* if no service is being tracked */
return null;
}
int index = 0;
if (length > 1) { /* if more than one service, select highest ranking */
int rankings[] = new int[length];
int count = 0;
int maxRanking = Integer.MIN_VALUE;
for (int i = 0; i < length; i++) {
Object property = references[i]
.getProperty(Constants.SERVICE_RANKING);
int ranking = (property instanceof Integer) ? ((Integer) property)
.intValue()
: 0;
rankings[i] = ranking;
if (ranking > maxRanking) {
index = i;
maxRanking = ranking;
count = 1;
}
else {
if (ranking == maxRanking) {
count++;
}
}
}
if (count > 1) { /* if still more than one service, select lowest id */
long minId = Long.MAX_VALUE;
for (int i = 0; i < length; i++) {
if (rankings[i] == maxRanking) {
long id = ((Long) (references[i]
.getProperty(Constants.SERVICE_ID)))
.longValue();
if (id < minId) {
index = i;
minId = id;
}
}
}
}
}
return cachedReference = references[index];
}
/**
* Returns the service object for the specified
* ServiceReference if the specified referenced service is
* being tracked by this ServiceTracker.
*
* @param reference The reference to the desired service.
* @return A service object or null if the service referenced
* by the specified ServiceReference is not being
* tracked.
*/
public Object getService(ServiceReference reference) {
final Tracked t = tracked();
if (t == null) { /* if ServiceTracker is not open */
return null;
}
synchronized (t) {
return t.getCustomizedObject(reference);
}
}
/**
* Return an array of service objects for all services being tracked by this
* ServiceTracker.
*
*
* This implementation calls {@link #getServiceReferences()} to get the list
* of references for the tracked services and then calls
* {@link #getService(ServiceReference)} for each reference to get the
* tracked service object.
*
* @return An array of service objects or null if no services
* are being tracked.
*/
public Object[] getServices() {
final Tracked t = tracked();
if (t == null) { /* if ServiceTracker is not open */
return null;
}
synchronized (t) {
ServiceReference[] references = getServiceReferences();
int length = (references == null) ? 0 : references.length;
if (length == 0) {
return null;
}
Object[] objects = new Object[length];
for (int i = 0; i < length; i++) {
objects[i] = getService(references[i]);
}
return objects;
}
}
/**
* Returns a service object for one of the services being tracked by this
* ServiceTracker.
*
*
* If any services are being tracked, this implementation returns the result
* of calling getService(getServiceReference()).
*
* @return A service object or null if no services are being
* tracked.
*/
public Object getService() {
Object service = cachedService;
if (service != null) {
if (DEBUG) {
System.out
.println("ServiceTracker.getService[cached]: "
+ filter);
}
return service;
}
if (DEBUG) {
System.out.println("ServiceTracker.getService: " + filter);
}
ServiceReference reference = getServiceReference();
if (reference == null) {
return null;
}
return cachedService = getService(reference);
}
/**
* Remove a service from this ServiceTracker.
*
* The specified service will be removed from this
* ServiceTracker. If the specified service was being tracked
* then the ServiceTrackerCustomizer.removedService method will
* be called for that service.
*
* @param reference The reference to the service to be removed.
*/
public void remove(ServiceReference reference) {
final Tracked t = tracked();
if (t == null) { /* if ServiceTracker is not open */
return;
}
t.untrack(reference, null);
}
/**
* Return the number of services being tracked by this
* ServiceTracker.
*
* @return The number of services being tracked.
*/
public int size() {
final Tracked t = tracked();
if (t == null) { /* if ServiceTracker is not open */
return 0;
}
synchronized (t) {
return t.size();
}
}
/**
* Returns the tracking count for this ServiceTracker.
*
* The tracking count is initialized to 0 when this
* ServiceTracker is opened. Every time a service is added,
* modified or removed from this ServiceTracker, the tracking
* count is incremented.
*
*
* The tracking count can be used to determine if this
* ServiceTracker has added, modified or removed a service by
* comparing a tracking count value previously collected with the current
* tracking count value. If the value has not changed, then no service has
* been added, modified or removed from this ServiceTracker
* since the previous tracking count was collected.
*
* @since 1.2
* @return The tracking count for this ServiceTracker or -1 if
* this ServiceTracker is not open.
*/
public int getTrackingCount() {
final Tracked t = tracked();
if (t == null) { /* if ServiceTracker is not open */
return -1;
}
synchronized (t) {
return t.getTrackingCount();
}
}
/**
* Called by the Tracked object whenever the set of tracked services is
* modified. Clears the cache.
*/
/*
* This method must not be synchronized since it is called by Tracked while
* Tracked is synchronized. We don't want synchronization interactions
* between the listener thread and the user thread.
*/
void modified() {
cachedReference = null; /* clear cached value */
cachedService = null; /* clear cached value */
if (DEBUG) {
System.out.println("ServiceTracker.modified: " + filter);
}
}
/**
* Inner class which subclasses AbstractTracked. This class is the
* ServiceListener object for the tracker.
*
* @ThreadSafe
*/
class Tracked extends AbstractTracked implements ServiceListener {
/**
* Tracked constructor.
*/
Tracked() {
super();
}
/**
* ServiceListener method for the
* ServiceTracker class. This method must NOT be
* synchronized to avoid deadlock potential.
*
* @param event ServiceEvent object from the framework.
*/
public void serviceChanged(final ServiceEvent event) {
/*
* Check if we had a delayed call (which could happen when we
* close).
*/
if (closed) {
return;
}
final ServiceReference reference = event.getServiceReference();
if (DEBUG) {
System.out
.println("ServiceTracker.Tracked.serviceChanged["
+ event.getType() + "]: " + reference);
}
switch (event.getType()) {
case ServiceEvent.REGISTERED :
case ServiceEvent.MODIFIED :
if (listenerFilter != null) { // service listener added with
// filter
track(reference, event);
/*
* If the customizer throws an unchecked exception, it
* is safe to let it propagate
*/
}
else { // service listener added without filter
if (filter.match(reference)) {
track(reference, event);
/*
* If the customizer throws an unchecked exception,
* it is safe to let it propagate
*/
}
else {
untrack(reference, event);
/*
* If the customizer throws an unchecked exception,
* it is safe to let it propagate
*/
}
}
break;
case ServiceEvent.MODIFIED_ENDMATCH :
case ServiceEvent.UNREGISTERING :
untrack(reference, event);
/*
* If the customizer throws an unchecked exception, it is
* safe to let it propagate
*/
break;
}
}
/**
* Increment the tracking count and tell the tracker there was a
* modification.
*
* @GuardedBy this
*/
void modified() {
super.modified(); /* increment the modification count */
ServiceTracker.this.modified();
}
/**
* Call the specific customizer adding method. This method must not be
* called while synchronized on this object.
*
* @param item Item to be tracked.
* @param related Action related object.
* @return Customized object for the tracked item or null
* if the item is not to be tracked.
*/
Object customizerAdding(final Object item,
final Object related) {
return customizer.addingService((ServiceReference) item);
}
/**
* Call the specific customizer modified method. This method must not be
* called while synchronized on this object.
*
* @param item Tracked item.
* @param related Action related object.
* @param object Customized object for the tracked item.
*/
void customizerModified(final Object item,
final Object related, final Object object) {
customizer.modifiedService((ServiceReference) item, object);
}
/**
* Call the specific customizer removed method. This method must not be
* called while synchronized on this object.
*
* @param item Tracked item.
* @param related Action related object.
* @param object Customized object for the tracked item.
*/
void customizerRemoved(final Object item,
final Object related, final Object object) {
customizer.removedService((ServiceReference) item, object);
}
}
/**
* Subclass of Tracked which implements the AllServiceListener interface.
* This class is used by the ServiceTracker if open is called with true.
*
* @since 1.3
* @ThreadSafe
*/
class AllTracked extends Tracked implements AllServiceListener {
/**
* AllTracked constructor.
*/
AllTracked() {
super();
}
}
}