Defer initialization of classpath to the background if called from main

Currently there are some bad behaving UI components in the eclipse IDE
that trigger resolving of the classpath containers in the process of
creating the UI, this leads to very bad startup performance and even
deadlocks in startup.

This now detects the issue, logs a warning of the offending component
and defer the initialization of classpath to a background job, this
currently decrease time from starting eclipse until UI is shown
noticeable.

Fix #1481

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

@@ -13,29 +13,86 @@
  *******************************************************************************/
 package org.eclipse.pde.internal.core;
 
+import java.lang.StackWalker.Option;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicBoolean;
+
 import org.eclipse.core.resources.IProject;
 import org.eclipse.core.runtime.CoreException;
+import org.eclipse.core.runtime.ILog;
 import org.eclipse.core.runtime.IPath;
 import org.eclipse.core.runtime.IStatus;
 import org.eclipse.core.runtime.Status;
+import org.eclipse.core.runtime.jobs.IJobChangeEvent;
 import org.eclipse.core.runtime.jobs.Job;
+import org.eclipse.core.runtime.jobs.JobChangeAdapter;
 import org.eclipse.jdt.core.ClasspathContainerInitializer;
 import org.eclipse.jdt.core.IClasspathContainer;
 import org.eclipse.jdt.core.IJavaProject;
 import org.eclipse.jdt.core.JavaCore;
+import org.eclipse.jdt.core.JavaModelException;
 import org.eclipse.pde.core.plugin.IPluginModelBase;
 
 public class RequiredPluginsInitializer extends ClasspathContainerInitializer {
 
+	private static final AtomicBoolean WARNING_LOGGED = new AtomicBoolean();
+
+	private static final Map<IJavaProject, Job> JOB_MAP = new ConcurrentHashMap<>();
+
 	private static final Job initPDEJob = Job.create(PDECoreMessages.PluginModelManager_InitializingPluginModels,
 			monitor -> {
 				if (!PDECore.getDefault().getModelManager().isInitialized()) {
 					PDECore.getDefault().getModelManager().targetReloaded(monitor);
 				}
 			});
 
+	private static StackWalker walker = StackWalker.getInstance(Option.RETAIN_CLASS_REFERENCE);
+
 	@Override
 	public void initialize(IPath containerPath, IJavaProject javaProject) throws CoreException {
+		if (isCalledWhileWorkbenchStartup()) {
+			// See https://github.com/eclipse-pde/eclipse.pde/issues/1481
+			if (WARNING_LOGGED.compareAndSet(false, true)) {
+				ILog.get().warn(
+						"RequiredPluginsInitializer called from within the Application startup thread this will badly impact your IDE performance!", //$NON-NLS-1$
+						new RuntimeException("Called from Application startup thread thread here")); //$NON-NLS-1$
+			}
+			JOB_MAP.compute(javaProject, (jp, oldjob) -> {
+				if (oldjob != null) {
+					oldjob.cancel();
+				}
+				Job job = Job.create(PDECoreMessages.PluginModelManager_InitializingPluginModels, m -> {
+					if (oldjob != null) {
+						try {
+							oldjob.join();
+						} catch (InterruptedException e) {
+						}
+					}
+					setClasspath(jp);
+				});
+				job.addJobChangeListener(new JobChangeAdapter() {
+					@Override
+					public void done(IJobChangeEvent event) {
+						JOB_MAP.remove(jp);
+					}
+				});
+				job.schedule();
+				return job;
+			});
+			return;
+		}
+		Job job = JOB_MAP.get(javaProject);
+		if (job != null) {
+			try {
+				job.join();
+			} catch (InterruptedException e) {
+			}
+		}
+		setClasspath(javaProject);
+	}
+
+	protected void setClasspath(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();
@@ -85,4 +142,14 @@ public void requestClasspathContainerUpdate(IPath containerPath, IJavaProject pr
 		JavaCore.setClasspathContainer(containerPath, new IJavaProject[] {project}, new IClasspathContainer[] {containerSuggestion}, null);
 	}
 
+	private static boolean isCalledWhileWorkbenchStartup() {
+
+		return walker.walk(frames -> {
+			return frames.anyMatch(sf -> {
+				return "org.eclipse.e4.ui.internal.workbench.E4Workbench".equals(sf.getClassName()) //$NON-NLS-1$
+						&& "createAndRunUI".equals(sf.getMethodName()); //$NON-NLS-1$
+			});
+		});
+	}
+
 }