org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/text/java/CompletionProposalComputerDescriptor.java - jdt/eclipse.jdt.ui - Git at Google

 /*******************************************************************************
  * Copyright (c) 2005, 2011 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  *     IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.jdt.internal.ui.text.java;

 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Set;

 import org.osgi.framework.Bundle;

 import org.eclipse.core.runtime.Assert;
 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.core.runtime.IConfigurationElement;
 import org.eclipse.core.runtime.IContributor;
 import org.eclipse.core.runtime.IExtension;
 import org.eclipse.core.runtime.IProgressMonitor;
 import org.eclipse.core.runtime.IStatus;
 import org.eclipse.core.runtime.InvalidRegistryObjectException;
 import org.eclipse.core.runtime.PerformanceStats;
 import org.eclipse.core.runtime.Platform;
 import org.eclipse.core.runtime.Status;

 import org.eclipse.jface.text.IDocument;
 import org.eclipse.jface.text.contentassist.ICompletionProposal;
 import org.eclipse.jface.text.contentassist.IContextInformation;

 import org.eclipse.jdt.internal.corext.util.Messages;

 import org.eclipse.jdt.ui.text.IJavaPartitions;
 import org.eclipse.jdt.ui.text.java.ContentAssistInvocationContext;
 import org.eclipse.jdt.ui.text.java.IJavaCompletionProposalComputer;

 import org.eclipse.jdt.internal.ui.JavaPlugin;

 /**
  * The description of an extension to the
  * <code>org.eclipse.jdt.ui.javaCompletionProposalComputer</code> extension point. Instances are
  * immutable. Instances can be obtained from a {@link CompletionProposalComputerRegistry}.
  *
  * @see CompletionProposalComputerRegistry
  * @since 3.2
  */
 final class CompletionProposalComputerDescriptor {
 	/** The default category id. */
 	private static final String DEFAULT_CATEGORY_ID= "org.eclipse.jdt.ui.defaultProposalCategory"; //$NON-NLS-1$
 	/** The extension schema name of the category id attribute. */
 	private static final String CATEGORY_ID= "categoryId"; //$NON-NLS-1$
 	/** The extension schema name of the partition type attribute. */
 	private static final String TYPE= "type"; //$NON-NLS-1$
 	/** The extension schema name of the class attribute. */
 	private static final String CLASS= "class"; //$NON-NLS-1$
 	/** The extension schema name of the activate attribute. */
 	private static final String ACTIVATE= "activate"; //$NON-NLS-1$
 	/** The extension schema name of the partition child elements. */
 	private static final String PARTITION= "partition"; //$NON-NLS-1$
 	/** Set of Java partition types. */
 	private static final Set<String> PARTITION_SET;
 	/** The name of the performance event used to trace extensions. */
 	private static final String PERFORMANCE_EVENT= JavaPlugin.getPluginId() + "/perf/content_assist/extensions"; //$NON-NLS-1$
 	/**
 	 * If <code>true</code>, execution time of extensions is measured and the data forwarded to
 	 * core's {@link PerformanceStats} service.
 	 */
 	private static final boolean MEASURE_PERFORMANCE= PerformanceStats.isEnabled(PERFORMANCE_EVENT);
 	/**
 	 * Independently of the {@link PerformanceStats} service, any operation that takes longer than
 	 * {@value} milliseconds will be flagged as an violation. This timeout does not apply to the
 	 * first invocation, as it may take longer due to plug-in initialization etc. See also
 	 * {@link #fIsReportingDelay}.
 	 */
 	private static final long MAX_DELAY= 5000;

 	/* log constants */
 	private static final String COMPUTE_COMPLETION_PROPOSALS= "computeCompletionProposals()"; //$NON-NLS-1$
 	private static final String COMPUTE_CONTEXT_INFORMATION= "computeContextInformation()"; //$NON-NLS-1$
 	private static final String SESSION_STARTED= "sessionStarted()"; //$NON-NLS-1$
 	private static final String SESSION_ENDED= "sessionEnded()"; //$NON-NLS-1$

 	static {
 		Set<String> partitions= new HashSet<String>();
 		partitions.add(IDocument.DEFAULT_CONTENT_TYPE);
 		partitions.add(IJavaPartitions.JAVA_DOC);
 		partitions.add(IJavaPartitions.JAVA_MULTI_LINE_COMMENT);
 		partitions.add(IJavaPartitions.JAVA_SINGLE_LINE_COMMENT);
 		partitions.add(IJavaPartitions.JAVA_STRING);
 		partitions.add(IJavaPartitions.JAVA_CHARACTER);

 		PARTITION_SET= Collections.unmodifiableSet(partitions);
 	}

 	/** The identifier of the extension. */
 	private final String fId;
 	/** The name of the extension. */
 	private final String fName;
 	/** The class name of the provided <code>IJavaCompletionProposalComputer</code>. */
 	private final String fClass;
 	/** The activate attribute value. */
 	private final boolean fActivate;
 	/** The partition of the extension (element type: {@link String}). */
 	private final Set<String> fPartitions;
 	/** The configuration element of this extension. */
 	private final IConfigurationElement fElement;
 	/** The registry we are registered with. */
 	private final CompletionProposalComputerRegistry fRegistry;
 	/** The computer, if instantiated, <code>null</code> otherwise. */
 	private IJavaCompletionProposalComputer fComputer;
 	/** The ui category. */
 	private final CompletionProposalCategory fCategory;
 	/** The first error message in the most recent operation, or <code>null</code>. */
 	private String fLastError;
 	/**
 	 * Tells whether to inform the user when <code>MAX_DELAY</code> has been exceeded.
 	 * We start timing execution after the first session because the first may take
 	 * longer due to plug-in activation and initialization.
 	 */
 	private boolean fIsReportingDelay= false;
 	/** The start of the last operation. */
 	private long fStart;
 	/**
 	 * Tells whether we tried to load the computer.
 	 * @since 3.4
 	 */
 	boolean fTriedLoadingComputer= false;


 	/**
 	 * Creates a new descriptor.
 	 *
 	 * @param element the configuration element to read
 	 * @param registry the computer registry creating this descriptor
 	 * @param categories the categories
 	 * @throws InvalidRegistryObjectException if this extension is no longer valid
 	 * @throws CoreException if the extension contains invalid values
 	 */
 	CompletionProposalComputerDescriptor(IConfigurationElement element, CompletionProposalComputerRegistry registry, List<CompletionProposalCategory> categories) throws InvalidRegistryObjectException, CoreException {
 		Assert.isLegal(registry != null);
 		Assert.isLegal(element != null);

 		fRegistry= registry;
 		fElement= element;
 		IExtension extension= element.getDeclaringExtension();
 		fId= extension.getUniqueIdentifier();
 		checkNotNull(fId, "id"); //$NON-NLS-1$

 		String name= extension.getLabel();
 		if (name.length() == 0)
 			fName= fId;
 		else
 			fName= name;

 		Set<String> partitions= new HashSet<String>();
 		IConfigurationElement[] children= element.getChildren(PARTITION);
 		if (children.length == 0) {
 			fPartitions= PARTITION_SET; // add to all partition types if no partition is configured
 		} else {
 			for (int i= 0; i < children.length; i++) {
 				String type= children[i].getAttribute(TYPE);
 				checkNotNull(type, TYPE);
 				partitions.add(type);
 			}
 			fPartitions= Collections.unmodifiableSet(partitions);
 		}

 		String activateAttribute= element.getAttribute(ACTIVATE);
 		fActivate= Boolean.valueOf(activateAttribute).booleanValue();

 		fClass= element.getAttribute(CLASS);
 		checkNotNull(fClass, CLASS);

 		String categoryId= element.getAttribute(CATEGORY_ID);
 		if (categoryId == null)
 			categoryId= DEFAULT_CATEGORY_ID;
 		CompletionProposalCategory category= null;
 		for (Iterator<CompletionProposalCategory> it= categories.iterator(); it.hasNext();) {
 			CompletionProposalCategory cat= it.next();
 			if (cat.getId().equals(categoryId)) {
 				category= cat;
 				break;
 			}
 		}
 		if (category == null) {
 			// create a category if it does not exist
 			fCategory= new CompletionProposalCategory(categoryId, fName, registry);
 			categories.add(fCategory);
 		} else {
 			fCategory= category;
 		}
 	}

 	/**
 	 * Checks that the given attribute value is not <code>null</code>.
 	 *
 	 * @param value the object to check if not null
 	 * @param attribute the attribute
 	 * @throws InvalidRegistryObjectException if the registry element is no longer valid
 	 * @throws CoreException if <code>value</code> is <code>null</code>
 	 */
 	private void checkNotNull(Object value, String attribute) throws InvalidRegistryObjectException, CoreException {
 		if (value == null) {
 			Object[] args= { getId(), fElement.getContributor().getName(), attribute };
 			String message= Messages.format(JavaTextMessages.CompletionProposalComputerDescriptor_illegal_attribute_message, args);
 			IStatus status= new Status(IStatus.WARNING, JavaPlugin.getPluginId(), IStatus.OK, message, null);
 			throw new CoreException(status);
 		}
 	}

 	/**
 	 * Returns the identifier of the described extension.
 	 *
 	 * @return Returns the id
 	 */
 	public String getId() {
 		return fId;
 	}

 	/**
 	 * Returns the name of the described extension.
 	 *
 	 * @return Returns the name
 	 */
 	public String getName() {
 		return fName;
 	}

 	/**
 	 * Returns the partition types of the described extension.
 	 *
 	 * @return the set of partition types (element type: {@link String})
 	 */
 	public Set<String> getPartitions() {
 		return fPartitions;
 	}

 	/**
 	 * Returns a cached instance of the computer as described in the
 	 * extension's xml. If the computer is not yet created and
 	 * <code>canCreate</code> is <code>true</code> then {@link #createComputer()}
 	 * is called and the result cached.
 	 *
 	 * @param canCreate <code>true</code> if the proposal computer can be created
 	 * @return a new instance of the completion proposal computer as
 	 *         described by this descriptor
 	 * @throws CoreException if the creation fails
 	 * @throws InvalidRegistryObjectException if the extension is not
 	 *         valid any longer (e.g. due to plug-in unloading)
 	 */
 	private synchronized IJavaCompletionProposalComputer getComputer(boolean canCreate) throws CoreException, InvalidRegistryObjectException {
 		if (fComputer == null && canCreate && !fTriedLoadingComputer && (fActivate || isPluginLoaded())) {
 			fTriedLoadingComputer= true;
 			fComputer= createComputer();
 		}
 		return fComputer;
 	}

 	private boolean isPluginLoaded() {
 		Bundle bundle= getBundle();
 		return bundle != null && bundle.getState() == Bundle.ACTIVE;
 	}

 	private Bundle getBundle() {
 		String namespace= fElement.getDeclaringExtension().getContributor().getName();
 		Bundle bundle= Platform.getBundle(namespace);
 		return bundle;
 	}

 	/**
 	 * Returns a new instance of the computer as described in the
 	 * extension's xml. Note that the safest way to access the computer
 	 * is by using the
 	 * {@linkplain #computeCompletionProposals(ContentAssistInvocationContext, IProgressMonitor) computeCompletionProposals}
 	 * and
 	 * {@linkplain #computeContextInformation(ContentAssistInvocationContext, IProgressMonitor) computeContextInformation}
 	 * methods. These delegate the functionality to the contributed
 	 * computer, but handle instance creation and any exceptions thrown.
 	 *
 	 * @return a new instance of the completion proposal computer as
 	 *         described by this descriptor
 	 * @throws CoreException if the creation fails
 	 * @throws InvalidRegistryObjectException if the extension is not
 	 *         valid any longer (e.g. due to plug-in unloading)
 	 */
 	public IJavaCompletionProposalComputer createComputer() throws CoreException, InvalidRegistryObjectException {
 		return (IJavaCompletionProposalComputer) fElement.createExecutableExtension(CLASS);
 	}

 	/**
 	 * Safely computes completion proposals through the described extension. If the extension
 	 * is disabled, throws an exception or otherwise does not adhere to the contract described in
 	 * {@link IJavaCompletionProposalComputer}, an empty list is returned.
 	 *
 	 * @param context the invocation context passed on to the extension
 	 * @param monitor the progress monitor passed on to the extension
 	 * @return the list of computed completion proposals (element type:
 	 *         {@link org.eclipse.jface.text.contentassist.ICompletionProposal})
 	 */
 	public List<ICompletionProposal> computeCompletionProposals(ContentAssistInvocationContext context, IProgressMonitor monitor) {
 		if (!isEnabled())
 			return Collections.emptyList();

 		IStatus status;
 		try {
 			IJavaCompletionProposalComputer computer= getComputer(true);
 			if (computer == null) // not active yet
 				return Collections.emptyList();

 			try {
 				PerformanceStats stats= startMeter(context, computer);
 				List<ICompletionProposal> proposals= computer.computeCompletionProposals(context, monitor);
 				stopMeter(stats, COMPUTE_COMPLETION_PROPOSALS);

 				if (proposals != null) {
 					fLastError= computer.getErrorMessage();
 					return proposals;
 				}
 			} finally {
 				fIsReportingDelay= true;
 			}
 			status= createAPIViolationStatus(COMPUTE_COMPLETION_PROPOSALS);
 		} catch (InvalidRegistryObjectException x) {
 			status= createExceptionStatus(x);
 		} catch (CoreException x) {
 			status= createExceptionStatus(x);
 		} catch (RuntimeException x) {
 			status= createExceptionStatus(x);
 		} finally {
 			monitor.done();
 		}

 		fRegistry.informUser(this, status);

 		return Collections.emptyList();
 	}

 	/**
 	 * Safely computes context information objects through the described extension. If the extension
 	 * is disabled, throws an exception or otherwise does not adhere to the contract described in
 	 * {@link IJavaCompletionProposalComputer}, an empty list is returned.
 	 *
 	 * @param context the invocation context passed on to the extension
 	 * @param monitor the progress monitor passed on to the extension
 	 * @return the list of computed context information objects (element type:
 	 *         {@link org.eclipse.jface.text.contentassist.IContextInformation})
 	 */
 	public List<IContextInformation> computeContextInformation(ContentAssistInvocationContext context, IProgressMonitor monitor) {
 		if (!isEnabled())
 			return Collections.emptyList();

 		IStatus status;
 		try {
 			IJavaCompletionProposalComputer computer= getComputer(true);
 			if (computer == null) // not active yet
 				return Collections.emptyList();

 			PerformanceStats stats= startMeter(context, computer);
 			List<IContextInformation> proposals= computer.computeContextInformation(context, monitor);
 			stopMeter(stats, COMPUTE_CONTEXT_INFORMATION);

 			if (proposals != null) {
 				fLastError= computer.getErrorMessage();
 				return proposals;
 			}

 			status= createAPIViolationStatus(COMPUTE_CONTEXT_INFORMATION);
 		} catch (InvalidRegistryObjectException x) {
 			status= createExceptionStatus(x);
 		} catch (CoreException x) {
 			status= createExceptionStatus(x);
 		} catch (RuntimeException x) {
 			status= createExceptionStatus(x);
 		} finally {
 			monitor.done();
 		}

 		fRegistry.informUser(this, status);

 		return Collections.emptyList();
 	}


 	/**
 	 * Notifies the described extension of a proposal computation session start.
 	 * <p><em>
 	 * Note: This method is called every time code assist is invoked and
 	 * is <strong>not</strong> filtered by partition type.
 	 * </em></p>
 	 */
 	public void sessionStarted() {
 		if (!isEnabled())
 			return;

 		IStatus status;
 		try {
 			IJavaCompletionProposalComputer computer= getComputer(true);
 			if (computer == null) // not active yet
 				return;

 			PerformanceStats stats= startMeter(SESSION_STARTED, computer);
 			computer.sessionStarted();
 			stopMeter(stats, SESSION_ENDED);

 			return;
 		} catch (InvalidRegistryObjectException x) {
 			status= createExceptionStatus(x);
 		} catch (CoreException x) {
 			status= createExceptionStatus(x);
 		} catch (RuntimeException x) {
 			status= createExceptionStatus(x);
 		}

 		fRegistry.informUser(this, status);
 	}

 	/**
 	 * Notifies the described extension of a proposal computation session end.
 	 * <p><em>
 	 * Note: This method is called every time code assist is invoked and
 	 * is <strong>not</strong> filtered by partition type.
 	 * </em></p>
 	 */
 	public void sessionEnded() {
 		if (!isEnabled())
 			return;

 		IStatus status;
 		try {
 			IJavaCompletionProposalComputer computer= getComputer(false);
 			if (computer == null) // not active yet
 				return;

 			PerformanceStats stats= startMeter(SESSION_ENDED, computer);
 			computer.sessionEnded();
 			stopMeter(stats, SESSION_ENDED);

 			return;
 		} catch (InvalidRegistryObjectException x) {
 			status= createExceptionStatus(x);
 		} catch (CoreException x) {
 			status= createExceptionStatus(x);
 		} catch (RuntimeException x) {
 			status= createExceptionStatus(x);
 		}

 		fRegistry.informUser(this, status);
 	}

 	private PerformanceStats startMeter(Object context, IJavaCompletionProposalComputer computer) {
 		final PerformanceStats stats;
 		if (MEASURE_PERFORMANCE) {
 			stats= PerformanceStats.getStats(PERFORMANCE_EVENT, computer);
 			stats.startRun(context.toString());
 		} else {
 			stats= null;
 		}

 		if (fIsReportingDelay) {
 			fStart= System.currentTimeMillis();
 		}

 		return stats;
 	}

 	private void stopMeter(final PerformanceStats stats, String operation) {
 		if (MEASURE_PERFORMANCE) {
 			stats.endRun();
 			if (stats.isFailure()) {
 				IStatus status= createPerformanceStatus(operation);
 				fRegistry.informUser(this, status);
 				return;
 			}
 		}

 		if (fIsReportingDelay) {
 			long current= System.currentTimeMillis();
 			if (current - fStart > MAX_DELAY) {
 				IStatus status= createPerformanceStatus(operation);
 				fRegistry.informUser(this, status);
 			}
 		}
 	}

 	private IStatus createExceptionStatus(InvalidRegistryObjectException x) {
 		// extension has become invalid - log & disable
 		String blame= createBlameMessage();
 		String reason= JavaTextMessages.CompletionProposalComputerDescriptor_reason_invalid;
 		return new Status(IStatus.INFO, JavaPlugin.getPluginId(), IStatus.OK, blame + " " + reason, x); //$NON-NLS-1$
 	}

 	private IStatus createExceptionStatus(CoreException x) {
 		// unable to instantiate the extension - log
 		String blame= createBlameMessage();
 		String reason= JavaTextMessages.CompletionProposalComputerDescriptor_reason_instantiation;
 		return new Status(IStatus.ERROR, JavaPlugin.getPluginId(), IStatus.OK, blame + " " + reason, x); //$NON-NLS-1$
 	}

 	private IStatus createExceptionStatus(RuntimeException x) {
 		// misbehaving extension - log
 		String blame= createBlameMessage();
 		String reason= JavaTextMessages.CompletionProposalComputerDescriptor_reason_runtime_ex;
 		return new Status(IStatus.WARNING, JavaPlugin.getPluginId(), IStatus.OK, blame + " " + reason, x); //$NON-NLS-1$
 	}

 	private IStatus createAPIViolationStatus(String operation) {
 		String blame= createBlameMessage();
 		Object[] args= {operation};
 		String reason= Messages.format(JavaTextMessages.CompletionProposalComputerDescriptor_reason_API, args);
 		return new Status(IStatus.WARNING, JavaPlugin.getPluginId(), IStatus.OK, blame + " " + reason, null); //$NON-NLS-1$
 	}

 	private IStatus createPerformanceStatus(String operation) {
 		String blame= createBlameMessage();
 		Object[] args= {operation};
 		String reason= Messages.format(JavaTextMessages.CompletionProposalComputerDescriptor_reason_performance, args);
 		return new Status(IStatus.WARNING, JavaPlugin.getPluginId(), IStatus.OK, blame + " " + reason, null); //$NON-NLS-1$
 	}

 	private String createBlameMessage() {
 		Object[] args= { getName(), fElement.getDeclaringExtension().getContributor().getName() };
 		String disable= Messages.format( JavaTextMessages.CompletionProposalComputerDescriptor_blame_message, args);
 		return disable;
 	}

 	/**
 	 * Returns the enablement state of the described extension.
 	 *
 	 * @return the enablement state of the described extension
 	 */
 	private boolean isEnabled() {
 		return fCategory.isEnabled();
 	}

 	CompletionProposalCategory getCategory() {
 		return fCategory;
 	}

 	/**
 	 * Returns the error message from the described extension.
 	 *
 	 * @return the error message from the described extension
 	 */
 	public String getErrorMessage() {
 		return fLastError;
 	}

 	/**
 	 * Returns the contributor of the described extension.
 	 *
 	 * @return the contributor of the described extension
 	 */
     IContributor getContributor()  {
         try {
 	        return fElement.getContributor();
         } catch (InvalidRegistryObjectException e) {
         	return null;
         }
     }

 }
	/*******************************************************************************
	* Copyright (c) 2005, 2011 IBM Corporation and others.
	* All rights reserved. This program and the accompanying materials
	* are made available under the terms of the Eclipse Public License v1.0
	* which accompanies this distribution, and is available at
	* http://www.eclipse.org/legal/epl-v10.html
	*
	* Contributors:
	* IBM Corporation - initial API and implementation
	*******************************************************************************/
	package org.eclipse.jdt.internal.ui.text.java;

	import java.util.Collections;
	import java.util.HashSet;
	import java.util.Iterator;
	import java.util.List;
	import java.util.Set;

	import org.osgi.framework.Bundle;

	import org.eclipse.core.runtime.Assert;
	import org.eclipse.core.runtime.CoreException;
	import org.eclipse.core.runtime.IConfigurationElement;
	import org.eclipse.core.runtime.IContributor;
	import org.eclipse.core.runtime.IExtension;
	import org.eclipse.core.runtime.IProgressMonitor;
	import org.eclipse.core.runtime.IStatus;
	import org.eclipse.core.runtime.InvalidRegistryObjectException;
	import org.eclipse.core.runtime.PerformanceStats;
	import org.eclipse.core.runtime.Platform;
	import org.eclipse.core.runtime.Status;

	import org.eclipse.jface.text.IDocument;
	import org.eclipse.jface.text.contentassist.ICompletionProposal;
	import org.eclipse.jface.text.contentassist.IContextInformation;

	import org.eclipse.jdt.internal.corext.util.Messages;

	import org.eclipse.jdt.ui.text.IJavaPartitions;
	import org.eclipse.jdt.ui.text.java.ContentAssistInvocationContext;
	import org.eclipse.jdt.ui.text.java.IJavaCompletionProposalComputer;

	import org.eclipse.jdt.internal.ui.JavaPlugin;

	/**
	* The description of an extension to the
	* <code>org.eclipse.jdt.ui.javaCompletionProposalComputer</code> extension point. Instances are
	* immutable. Instances can be obtained from a {@link CompletionProposalComputerRegistry}.
	*
	* @see CompletionProposalComputerRegistry
	* @since 3.2
	*/
	final class CompletionProposalComputerDescriptor {
	/** The default category id. */
	private static final String DEFAULT_CATEGORY_ID= "org.eclipse.jdt.ui.defaultProposalCategory"; //$NON-NLS-1$
	/** The extension schema name of the category id attribute. */
	private static final String CATEGORY_ID= "categoryId"; //$NON-NLS-1$
	/** The extension schema name of the partition type attribute. */
	private static final String TYPE= "type"; //$NON-NLS-1$
	/** The extension schema name of the class attribute. */
	private static final String CLASS= "class"; //$NON-NLS-1$
	/** The extension schema name of the activate attribute. */
	private static final String ACTIVATE= "activate"; //$NON-NLS-1$
	/** The extension schema name of the partition child elements. */
	private static final String PARTITION= "partition"; //$NON-NLS-1$
	/** Set of Java partition types. */
	private static final Set<String> PARTITION_SET;
	/** The name of the performance event used to trace extensions. */
	private static final String PERFORMANCE_EVENT= JavaPlugin.getPluginId() + "/perf/content_assist/extensions"; //$NON-NLS-1$
	/**
	* If <code>true</code>, execution time of extensions is measured and the data forwarded to
	* core's {@link PerformanceStats} service.
	*/
	private static final boolean MEASURE_PERFORMANCE= PerformanceStats.isEnabled(PERFORMANCE_EVENT);
	/**
	* Independently of the {@link PerformanceStats} service, any operation that takes longer than
	* {@value} milliseconds will be flagged as an violation. This timeout does not apply to the
	* first invocation, as it may take longer due to plug-in initialization etc. See also
	* {@link #fIsReportingDelay}.
	*/
	private static final long MAX_DELAY= 5000;

	/* log constants */
	private static final String COMPUTE_COMPLETION_PROPOSALS= "computeCompletionProposals()"; //$NON-NLS-1$
	private static final String COMPUTE_CONTEXT_INFORMATION= "computeContextInformation()"; //$NON-NLS-1$
	private static final String SESSION_STARTED= "sessionStarted()"; //$NON-NLS-1$
	private static final String SESSION_ENDED= "sessionEnded()"; //$NON-NLS-1$

	static {
	Set<String> partitions= new HashSet<String>();
	partitions.add(IDocument.DEFAULT_CONTENT_TYPE);
	partitions.add(IJavaPartitions.JAVA_DOC);
	partitions.add(IJavaPartitions.JAVA_MULTI_LINE_COMMENT);
	partitions.add(IJavaPartitions.JAVA_SINGLE_LINE_COMMENT);
	partitions.add(IJavaPartitions.JAVA_STRING);
	partitions.add(IJavaPartitions.JAVA_CHARACTER);

	PARTITION_SET= Collections.unmodifiableSet(partitions);
	}

	/** The identifier of the extension. */
	private final String fId;
	/** The name of the extension. */
	private final String fName;
	/** The class name of the provided <code>IJavaCompletionProposalComputer</code>. */
	private final String fClass;
	/** The activate attribute value. */
	private final boolean fActivate;
	/** The partition of the extension (element type: {@link String}). */
	private final Set<String> fPartitions;
	/** The configuration element of this extension. */
	private final IConfigurationElement fElement;
	/** The registry we are registered with. */
	private final CompletionProposalComputerRegistry fRegistry;
	/** The computer, if instantiated, <code>null</code> otherwise. */
	private IJavaCompletionProposalComputer fComputer;
	/** The ui category. */
	private final CompletionProposalCategory fCategory;
	/** The first error message in the most recent operation, or <code>null</code>. */
	private String fLastError;
	/**
	* Tells whether to inform the user when <code>MAX_DELAY</code> has been exceeded.
	* We start timing execution after the first session because the first may take
	* longer due to plug-in activation and initialization.
	*/
	private boolean fIsReportingDelay= false;
	/** The start of the last operation. */
	private long fStart;
	/**
	* Tells whether we tried to load the computer.
	* @since 3.4
	*/
	boolean fTriedLoadingComputer= false;


	/**
	* Creates a new descriptor.
	*
	* @param element the configuration element to read
	* @param registry the computer registry creating this descriptor
	* @param categories the categories
	* @throws InvalidRegistryObjectException if this extension is no longer valid
	* @throws CoreException if the extension contains invalid values
	*/
	CompletionProposalComputerDescriptor(IConfigurationElement element, CompletionProposalComputerRegistry registry, List<CompletionProposalCategory> categories) throws InvalidRegistryObjectException, CoreException {
	Assert.isLegal(registry != null);
	Assert.isLegal(element != null);

	fRegistry= registry;
	fElement= element;
	IExtension extension= element.getDeclaringExtension();
	fId= extension.getUniqueIdentifier();
	checkNotNull(fId, "id"); //$NON-NLS-1$

	String name= extension.getLabel();
	if (name.length() == 0)
	fName= fId;
	else
	fName= name;

	Set<String> partitions= new HashSet<String>();
	IConfigurationElement[] children= element.getChildren(PARTITION);
	if (children.length == 0) {
	fPartitions= PARTITION_SET; // add to all partition types if no partition is configured
	} else {
	for (int i= 0; i < children.length; i++) {
	String type= children[i].getAttribute(TYPE);
	checkNotNull(type, TYPE);
	partitions.add(type);
	}
	fPartitions= Collections.unmodifiableSet(partitions);
	}

	String activateAttribute= element.getAttribute(ACTIVATE);
	fActivate= Boolean.valueOf(activateAttribute).booleanValue();

	fClass= element.getAttribute(CLASS);
	checkNotNull(fClass, CLASS);

	String categoryId= element.getAttribute(CATEGORY_ID);
	if (categoryId == null)
	categoryId= DEFAULT_CATEGORY_ID;
	CompletionProposalCategory category= null;
	for (Iterator<CompletionProposalCategory> it= categories.iterator(); it.hasNext();) {
	CompletionProposalCategory cat= it.next();
	if (cat.getId().equals(categoryId)) {
	category= cat;
	break;
	}
	}
	if (category == null) {
	// create a category if it does not exist
	fCategory= new CompletionProposalCategory(categoryId, fName, registry);
	categories.add(fCategory);
	} else {
	fCategory= category;
	}
	}

	/**
	* Checks that the given attribute value is not <code>null</code>.
	*
	* @param value the object to check if not null
	* @param attribute the attribute
	* @throws InvalidRegistryObjectException if the registry element is no longer valid
	* @throws CoreException if <code>value</code> is <code>null</code>
	*/
	private void checkNotNull(Object value, String attribute) throws InvalidRegistryObjectException, CoreException {
	if (value == null) {
	Object[] args= { getId(), fElement.getContributor().getName(), attribute };
	String message= Messages.format(JavaTextMessages.CompletionProposalComputerDescriptor_illegal_attribute_message, args);
	IStatus status= new Status(IStatus.WARNING, JavaPlugin.getPluginId(), IStatus.OK, message, null);
	throw new CoreException(status);
	}
	}

	/**
	* Returns the identifier of the described extension.
	*
	* @return Returns the id
	*/
	public String getId() {
	return fId;
	}

	/**
	* Returns the name of the described extension.
	*
	* @return Returns the name
	*/
	public String getName() {
	return fName;
	}

	/**
	* Returns the partition types of the described extension.
	*
	* @return the set of partition types (element type: {@link String})
	*/
	public Set<String> getPartitions() {
	return fPartitions;
	}

	/**
	* Returns a cached instance of the computer as described in the
	* extension's xml. If the computer is not yet created and
	* <code>canCreate</code> is <code>true</code> then {@link #createComputer()}
	* is called and the result cached.
	*
	* @param canCreate <code>true</code> if the proposal computer can be created
	* @return a new instance of the completion proposal computer as
	* described by this descriptor
	* @throws CoreException if the creation fails
	* @throws InvalidRegistryObjectException if the extension is not
	* valid any longer (e.g. due to plug-in unloading)
	*/
	private synchronized IJavaCompletionProposalComputer getComputer(boolean canCreate) throws CoreException, InvalidRegistryObjectException {
	if (fComputer == null && canCreate && !fTriedLoadingComputer && (fActivate \|\| isPluginLoaded())) {
	fTriedLoadingComputer= true;
	fComputer= createComputer();
	}
	return fComputer;
	}

	private boolean isPluginLoaded() {
	Bundle bundle= getBundle();
	return bundle != null && bundle.getState() == Bundle.ACTIVE;
	}

	private Bundle getBundle() {
	String namespace= fElement.getDeclaringExtension().getContributor().getName();
	Bundle bundle= Platform.getBundle(namespace);
	return bundle;
	}

	/**
	* Returns a new instance of the computer as described in the
	* extension's xml. Note that the safest way to access the computer
	* is by using the
	* {@linkplain #computeCompletionProposals(ContentAssistInvocationContext, IProgressMonitor) computeCompletionProposals}
	* and
	* {@linkplain #computeContextInformation(ContentAssistInvocationContext, IProgressMonitor) computeContextInformation}
	* methods. These delegate the functionality to the contributed
	* computer, but handle instance creation and any exceptions thrown.
	*
	* @return a new instance of the completion proposal computer as
	* described by this descriptor
	* @throws CoreException if the creation fails
	* @throws InvalidRegistryObjectException if the extension is not
	* valid any longer (e.g. due to plug-in unloading)
	*/
	public IJavaCompletionProposalComputer createComputer() throws CoreException, InvalidRegistryObjectException {
	return (IJavaCompletionProposalComputer) fElement.createExecutableExtension(CLASS);
	}

	/**
	* Safely computes completion proposals through the described extension. If the extension
	* is disabled, throws an exception or otherwise does not adhere to the contract described in
	* {@link IJavaCompletionProposalComputer}, an empty list is returned.
	*
	* @param context the invocation context passed on to the extension
	* @param monitor the progress monitor passed on to the extension
	* @return the list of computed completion proposals (element type:
	* {@link org.eclipse.jface.text.contentassist.ICompletionProposal})
	*/
	public List<ICompletionProposal> computeCompletionProposals(ContentAssistInvocationContext context, IProgressMonitor monitor) {
	if (!isEnabled())
	return Collections.emptyList();

	IStatus status;
	try {
	IJavaCompletionProposalComputer computer= getComputer(true);
	if (computer == null) // not active yet
	return Collections.emptyList();

	try {
	PerformanceStats stats= startMeter(context, computer);
	List<ICompletionProposal> proposals= computer.computeCompletionProposals(context, monitor);
	stopMeter(stats, COMPUTE_COMPLETION_PROPOSALS);

	if (proposals != null) {
	fLastError= computer.getErrorMessage();
	return proposals;
	}
	} finally {
	fIsReportingDelay= true;
	}
	status= createAPIViolationStatus(COMPUTE_COMPLETION_PROPOSALS);
	} catch (InvalidRegistryObjectException x) {
	status= createExceptionStatus(x);
	} catch (CoreException x) {
	status= createExceptionStatus(x);
	} catch (RuntimeException x) {
	status= createExceptionStatus(x);
	} finally {
	monitor.done();
	}

	fRegistry.informUser(this, status);

	return Collections.emptyList();
	}

	/**
	* Safely computes context information objects through the described extension. If the extension
	* is disabled, throws an exception or otherwise does not adhere to the contract described in
	* {@link IJavaCompletionProposalComputer}, an empty list is returned.
	*
	* @param context the invocation context passed on to the extension
	* @param monitor the progress monitor passed on to the extension
	* @return the list of computed context information objects (element type:
	* {@link org.eclipse.jface.text.contentassist.IContextInformation})
	*/
	public List<IContextInformation> computeContextInformation(ContentAssistInvocationContext context, IProgressMonitor monitor) {
	if (!isEnabled())
	return Collections.emptyList();

	IStatus status;
	try {
	IJavaCompletionProposalComputer computer= getComputer(true);
	if (computer == null) // not active yet
	return Collections.emptyList();

	PerformanceStats stats= startMeter(context, computer);
	List<IContextInformation> proposals= computer.computeContextInformation(context, monitor);
	stopMeter(stats, COMPUTE_CONTEXT_INFORMATION);

	if (proposals != null) {
	fLastError= computer.getErrorMessage();
	return proposals;
	}

	status= createAPIViolationStatus(COMPUTE_CONTEXT_INFORMATION);
	} catch (InvalidRegistryObjectException x) {
	status= createExceptionStatus(x);
	} catch (CoreException x) {
	status= createExceptionStatus(x);
	} catch (RuntimeException x) {
	status= createExceptionStatus(x);
	} finally {
	monitor.done();
	}

	fRegistry.informUser(this, status);

	return Collections.emptyList();
	}


	/**
	* Notifies the described extension of a proposal computation session start.
	* <p><em>
	* Note: This method is called every time code assist is invoked and
	* is <strong>not</strong> filtered by partition type.
	* </em></p>
	*/
	public void sessionStarted() {
	if (!isEnabled())
	return;

	IStatus status;
	try {
	IJavaCompletionProposalComputer computer= getComputer(true);
	if (computer == null) // not active yet
	return;

	PerformanceStats stats= startMeter(SESSION_STARTED, computer);
	computer.sessionStarted();
	stopMeter(stats, SESSION_ENDED);

	return;
	} catch (InvalidRegistryObjectException x) {
	status= createExceptionStatus(x);
	} catch (CoreException x) {
	status= createExceptionStatus(x);
	} catch (RuntimeException x) {
	status= createExceptionStatus(x);
	}

	fRegistry.informUser(this, status);
	}

	/**
	* Notifies the described extension of a proposal computation session end.
	* <p><em>
	* Note: This method is called every time code assist is invoked and
	* is <strong>not</strong> filtered by partition type.
	* </em></p>
	*/
	public void sessionEnded() {
	if (!isEnabled())
	return;

	IStatus status;
	try {
	IJavaCompletionProposalComputer computer= getComputer(false);
	if (computer == null) // not active yet
	return;

	PerformanceStats stats= startMeter(SESSION_ENDED, computer);
	computer.sessionEnded();
	stopMeter(stats, SESSION_ENDED);

	return;
	} catch (InvalidRegistryObjectException x) {
	status= createExceptionStatus(x);
	} catch (CoreException x) {
	status= createExceptionStatus(x);
	} catch (RuntimeException x) {
	status= createExceptionStatus(x);
	}

	fRegistry.informUser(this, status);
	}

	private PerformanceStats startMeter(Object context, IJavaCompletionProposalComputer computer) {
	final PerformanceStats stats;
	if (MEASURE_PERFORMANCE) {
	stats= PerformanceStats.getStats(PERFORMANCE_EVENT, computer);
	stats.startRun(context.toString());
	} else {
	stats= null;
	}

	if (fIsReportingDelay) {
	fStart= System.currentTimeMillis();
	}

	return stats;
	}

	private void stopMeter(final PerformanceStats stats, String operation) {
	if (MEASURE_PERFORMANCE) {
	stats.endRun();
	if (stats.isFailure()) {
	IStatus status= createPerformanceStatus(operation);
	fRegistry.informUser(this, status);
	return;
	}
	}

	if (fIsReportingDelay) {
	long current= System.currentTimeMillis();
	if (current - fStart > MAX_DELAY) {
	IStatus status= createPerformanceStatus(operation);
	fRegistry.informUser(this, status);
	}
	}
	}

	private IStatus createExceptionStatus(InvalidRegistryObjectException x) {
	// extension has become invalid - log & disable
	String blame= createBlameMessage();
	String reason= JavaTextMessages.CompletionProposalComputerDescriptor_reason_invalid;
	return new Status(IStatus.INFO, JavaPlugin.getPluginId(), IStatus.OK, blame + " " + reason, x); //$NON-NLS-1$
	}

	private IStatus createExceptionStatus(CoreException x) {
	// unable to instantiate the extension - log
	String blame= createBlameMessage();
	String reason= JavaTextMessages.CompletionProposalComputerDescriptor_reason_instantiation;
	return new Status(IStatus.ERROR, JavaPlugin.getPluginId(), IStatus.OK, blame + " " + reason, x); //$NON-NLS-1$
	}

	private IStatus createExceptionStatus(RuntimeException x) {
	// misbehaving extension - log
	String blame= createBlameMessage();
	String reason= JavaTextMessages.CompletionProposalComputerDescriptor_reason_runtime_ex;
	return new Status(IStatus.WARNING, JavaPlugin.getPluginId(), IStatus.OK, blame + " " + reason, x); //$NON-NLS-1$
	}

	private IStatus createAPIViolationStatus(String operation) {
	String blame= createBlameMessage();
	Object[] args= {operation};
	String reason= Messages.format(JavaTextMessages.CompletionProposalComputerDescriptor_reason_API, args);
	return new Status(IStatus.WARNING, JavaPlugin.getPluginId(), IStatus.OK, blame + " " + reason, null); //$NON-NLS-1$
	}

	private IStatus createPerformanceStatus(String operation) {
	String blame= createBlameMessage();
	Object[] args= {operation};
	String reason= Messages.format(JavaTextMessages.CompletionProposalComputerDescriptor_reason_performance, args);
	return new Status(IStatus.WARNING, JavaPlugin.getPluginId(), IStatus.OK, blame + " " + reason, null); //$NON-NLS-1$
	}

	private String createBlameMessage() {
	Object[] args= { getName(), fElement.getDeclaringExtension().getContributor().getName() };
	String disable= Messages.format( JavaTextMessages.CompletionProposalComputerDescriptor_blame_message, args);
	return disable;
	}

	/**
	* Returns the enablement state of the described extension.
	*
	* @return the enablement state of the described extension
	*/
	private boolean isEnabled() {
	return fCategory.isEnabled();
	}

	CompletionProposalCategory getCategory() {
	return fCategory;
	}

	/**
	* Returns the error message from the described extension.
	*
	* @return the error message from the described extension
	*/
	public String getErrorMessage() {
	return fLastError;
	}

	/**
	* Returns the contributor of the described extension.
	*
	* @return the contributor of the described extension
	*/
	IContributor getContributor() {
	try {
	return fElement.getContributor();
	} catch (InvalidRegistryObjectException e) {
	return null;
	}
	}

	}