/**
 * Update cycle markers for all java projects
 */
public static void updateAllCycleMarkers() throws JavaModelException {
	
	JavaModelManager manager = JavaModelManager.getJavaModelManager();
	IJavaProject[] projects = manager.getJavaModel().getJavaProjects();
	IWorkspaceRoot workspaceRoot = ResourcesPlugin.getWorkspace().getRoot();

	HashSet cycleParticipants = new HashSet();
	HashSet alreadyTraversed = new HashSet();
	int length = projects.length;
	
	// compute cycle participants
	ArrayList prereqChain = new ArrayList();
	for (int i = 0; i < length; i++){
		JavaProject project = (JavaProject)projects[i];
		if (!alreadyTraversed.contains(project)){
			prereqChain.clear();
			project.updateCycleParticipants(null, prereqChain, cycleParticipants, workspaceRoot, alreadyTraversed);
		}
	}
	
	for (int i = 0; i < length; i++){
		JavaProject project = (JavaProject)projects[i];
		
		if (cycleParticipants.contains(project)){
			IMarker cycleMarker = project.getCycleMarker();
			String circularCPOption = project.getOption(JavaCore.CORE_CIRCULAR_CLASSPATH, true);
			int circularCPSeverity = JavaCore.ERROR.equals(circularCPOption) ? IMarker.SEVERITY_ERROR : IMarker.SEVERITY_WARNING;
			if (cycleMarker != null) {
				// update existing cycle marker if needed
				try {
					int existingSeverity = ((Integer)cycleMarker.getAttribute(IMarker.SEVERITY)).intValue();
					if (existingSeverity != circularCPSeverity) {
						cycleMarker.setAttribute(IMarker.SEVERITY, circularCPSeverity);
					}
				} catch (CoreException e) {
					throw new JavaModelException(e);
				}
			} else {
				// create new marker
				project.createClasspathProblemMarker(
					new JavaModelStatus(IJavaModelStatusConstants.CLASSPATH_CYCLE, project)); 
			}
		} else {
			project.flushClasspathProblemMarkers(true, false);
		}			
	}
}

/**
 * If a cycle is detected, then cycleParticipants contains all the project involved in this cycle (directly and indirectly),
 * no cycle if the set is empty (and started empty)
 */
public void updateCycleParticipants(
		IClasspathEntry[] preferredClasspath, 
		ArrayList prereqChain, 
		HashSet cycleParticipants, 
		IWorkspaceRoot workspaceRoot,
		HashSet alreadyTraversed){
			
	prereqChain.add(this);
	try {
		IClasspathEntry[] classpath = preferredClasspath == null ? getResolvedClasspath(true) : preferredClasspath;
		for (int i = 0, length = classpath.length; i < length; i++) {
			IClasspathEntry entry = classpath[i];
			
			if (entry.getEntryKind() == IClasspathEntry.CPE_PROJECT){
				IPath entryPath = entry.getPath();
				IResource member = workspaceRoot.findMember(entryPath);
				if (member != null && member.getType() == IResource.PROJECT){
					JavaProject project = (JavaProject)JavaCore.create((IProject)member);
					int index = cycleParticipants.contains(project) ? 0 : prereqChain.indexOf(project);
					if (index >= 0) { // refer to cycle, or in cycle itself
						for (int size = prereqChain.size(); index < size; index++) {
							cycleParticipants.add(prereqChain.get(index)); 
						}
					} else {
						if (!alreadyTraversed.contains(project)) {
							project.updateCycleParticipants(null, prereqChain, cycleParticipants, workspaceRoot, alreadyTraversed);
						}
					}
				}
			}
		}
	} catch(JavaModelException e){
	}
	prereqChain.remove(this);
	alreadyTraversed.add(this);
}