Improve RequiredPluginsInitializer.initialize

- Collect deferred projects to be processed by a single job.

#1667

Author: merks

ui/org.eclipse.pde.core/src/org/eclipse/pde/internal/core/RequiredPluginsInitializer.java

@@ -13,9 +13,13 @@
  *******************************************************************************/
 package org.eclipse.pde.internal.core;
 
+import java.util.LinkedHashSet;
+import java.util.Set;
+
 import org.eclipse.core.resources.IProject;
 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.core.runtime.IPath;
+import org.eclipse.core.runtime.IProgressMonitor;
 import org.eclipse.core.runtime.IStatus;
 import org.eclipse.core.runtime.Status;
 import org.eclipse.core.runtime.jobs.Job;
@@ -35,24 +39,59 @@ public class RequiredPluginsInitializer extends ClasspathContainerInitializer {
 				}
 			});
 
+	private static final DeferredClasspathContainerInitializerJob deferredClasspathContainerInitializerJob = new DeferredClasspathContainerInitializerJob();
+
+	private static class DeferredClasspathContainerInitializerJob extends Job {
+
+		private final Set<IJavaProject> projects = new LinkedHashSet<>();
+
+		public DeferredClasspathContainerInitializerJob() {
+			// This name is not displayed to a user.
+			super("DeferredClasspathContainerInitializerJob"); //$NON-NLS-1$
+			setSystem(true);
+		}
+
+		public synchronized void initialize(IJavaProject project) {
+			if (projects.add(project)) {
+				schedule();
+			}
+		}
+
+		private synchronized IJavaProject[] consumeProjects() {
+			try {
+				return projects.toArray(IJavaProject[]::new);
+			} finally {
+				projects.clear();
+			}
+		}
+
+		@Override
+		protected IStatus run(IProgressMonitor monitor) {
+			for (IJavaProject project : consumeProjects()) {
+				try {
+					setupClasspath(project);
+				} catch (JavaModelException e) {
+					PDECore.log(e);
+				}
+			}
+			return Status.OK_STATUS;
+		}
+	}
+
 	@Override
 	public void initialize(IPath containerPath, IJavaProject javaProject) throws CoreException {
 		if (Job.getJobManager().isSuspended()) {
 			// if the jobmanager is currently suspended we can't use the
 			// schedule/join pattern here, instead we must retry the requested
 			// action once jobs are enabled again, this will the possibly
 			// trigger a rebuild if required or notify other listeners.
-			Job job = Job.create(PDECoreMessages.PluginModelManager_InitializingPluginModels, m -> {
-				setupClasspath(javaProject);
-			});
-			job.setSystem(true);
-			job.schedule();
+			deferredClasspathContainerInitializerJob.initialize(javaProject);
 		} else {
 			setupClasspath(javaProject);
 		}
 	}
 
-	protected void setupClasspath(IJavaProject javaProject) throws JavaModelException {
+	protected static void setupClasspath(IJavaProject javaProject) throws JavaModelException {
 		IProject project = javaProject.getProject();
 		// The first project to be built may initialize the PDE models, potentially long running, so allow cancellation
 		PluginModelManager manager = PDECore.getDefault().getModelManager();