Bug 53582 Rebuild Project are not run in the background?
The "Build All" and "Rebuild All" actions are run in the background, but the "Build Project" and "Rebuild Project" actions aren't. This is not consistent and I was surprised to get a modal dialog when performing a "Rebuild Project".
bundles/org.eclipse.ui.ide/extensions/org/eclipse/ui/actions/WorkspaceAction.java
*
	 * @return the problems dialog title
	 */
	String getProblemsTitle() {
		return IDEWorkbenchMessages.getString("WorkspaceAction.problemsTitle"); 
	}
	/**
	 * Returns the shell for this action. This shell is used for the modal progress
	 * and error dialogs.
	 *
	 * @return the shell
	 */
	Shell getShell() {
		return shell;
	}
	/**
	 * Performs this action's operation on each of the selected resources, reporting
	 * progress to, and fielding cancel requests from, the given progress monitor.
	 * <p>
	 * Note that this method is invoked in a non-UI thread.
	 * </p>
	 * <p>
	 * Subclasses must implement this method.
	 * </p>
	 *
	 * @param resource one of the selected resources
	 * @param monitor a progress monitor
	 * @exception CoreException if the operation fails
	 */
	abstract void invokeOperation(IResource resource, IProgressMonitor monitor)