### Eclipse Workspace Patch 1.0
#P org.eclipse.core.databinding
Index: src/org/eclipse/core/databinding/validation/MultiValidator.java
===================================================================
RCS file: /cvsroot/eclipse/org.eclipse.core.databinding/src/org/eclipse/core/databinding/validation/MultiValidator.java,v
retrieving revision 1.1
diff -u -r1.1 MultiValidator.java
--- src/org/eclipse/core/databinding/validation/MultiValidator.java	24 Mar 2008 22:55:58 -0000	1.1
+++ src/org/eclipse/core/databinding/validation/MultiValidator.java	17 Jun 2008 16:13:53 -0000
@@ -14,6 +14,7 @@
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.List;
 
 import org.eclipse.core.databinding.ValidationStatusProvider;
 import org.eclipse.core.databinding.observable.ChangeEvent;
@@ -195,14 +196,22 @@
 	}
 
 	private void revalidate() {
+		final StatusHandler handler = new StatusHandler() {
+			public void handleStatus(final IStatus status) {
+				realm.exec(new Runnable() {
+					public void run() {
+						validationStatus
+								.setValue(status == null ? ValidationStatus
+										.ok() : status);
+					}
+				});
+			}
+		};
 		final IObservable[] dependencies = ObservableTracker.runAndMonitor(
 				new Runnable() {
 					public void run() {
 						try {
-							IStatus status = validate();
-							if (status == null)
-								status = ValidationStatus.ok();
-							validationStatus.setValue(status);
+							validate(handler);
 						} catch (RuntimeException e) {
 							// Usually an NPE as dependencies are
 							// init'ed
@@ -213,12 +222,71 @@
 				}, null, null);
 		ObservableTracker.runAndIgnore(new Runnable() {
 			public void run() {
-				targets.clear();
-				targets.addAll(Arrays.asList(dependencies));
+				List dependencyList = new ArrayList(Arrays.asList(dependencies));
+				// remove old targets not in the new dependency list
+				targets.retainAll(dependencyList);
+				// remove targets in the new dependency list which are already
+				// known
+				dependencyList.removeAll(targets);
+				// add the new dependencies
+				targets.addAll(dependencyList);
 			}
 		});
 	}
 
+	interface StatusHandler {
+		void handleStatus(IStatus status);
+	}
+
+	/**
+	 * Calculates and passes the current validation status to the given
+	 * callback.
+	 * <p>
+	 * Note: To ensure that the validation status is kept current, all
+	 * dependencies used to calculate status should be accessed through
+	 * {@link IObservable} instances. Each dependency observable must be in the
+	 * same realm as the MultiValidator.
+	 * <p>
+	 * If validation is being performed asynchronously (i.e. in a different
+	 * thread), then the observables which are used to calculate validation
+	 * status should be accessed before forking, as follows:
+	 * 
+	 * <pre>
+	 * MultiValidator validator = new MultiValidator() {
+	 * 	protected void validate(final StatusHandler callback) {
+	 *      // Observables must be accessed in the calling thread
+	 * 		final Integer value0 = (Integer) middle0.getValue();
+	 * 		final Integer value1 = (Integer) middle1.getValue();
+	 * 		new Thread(new Runnable() {
+	 * 			public void run() {
+	 * 		        // Calculate the validation status
+	 * 				if (Math.abs(value0.intValue()) % 2 != Math.abs(value1
+	 * 						.intValue()) % 2) {
+	 *                  callback.handleStatus(ValidationStatus.error(
+	 *                      &quot;Values must be both even or both odd&quot;);
+	 *              } else {
+	 *                  callback.handleStatus(ValidationStatus.ok());
+	 *              }
+	 * 			}
+	 * 		}).start();
+	 * 	}
+	 * };
+	 * </pre>
+	 * 
+	 * @param callback
+	 *            the callback which is to receive the validation status. The
+	 *            callback may be called from outside the realm.
+	 */
+	protected void validate(StatusHandler callback) {
+		try {
+			callback.handleStatus(validate());
+		} catch (RuntimeException e) {
+			// Usually an NPE as dependencies are
+			// init'ed
+			callback.handleStatus(ValidationStatus.error(e.getMessage(), e));
+		}
+	}
+
 	/**
 	 * Return the current validation status.
 	 * <p>
@@ -229,7 +297,10 @@
 	 * 
 	 * @return the current validation status.
 	 */
-	protected abstract IStatus validate();
+	protected IStatus validate() {
+		throw new IllegalStateException(
+				"Subclasses must override one of the validate() methods"); //$NON-NLS-1$
+	}
 
 	/**
 	 * Returns a wrapper {@link IObservableValue} which stays in sync with the