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
/**
	 * The <code>WorkspaceAction</code> implementation of this
	 * <code>SelectionListenerAction</code> method ensures that this action is
	 * disabled if any of the selected resources are inaccessible. Subclasses may
	 * extend to react to selection changes; however, if the super method returns
	 * <code>false</code>, the overriding method should also return <code>false</code>.
	 */
	protected boolean updateSelection(IStructuredSelection selection) {
		if (!super.updateSelection(selection) || selection.isEmpty()) {
			return false;
		}
		for (Iterator i = getSelectedResources().iterator(); i.hasNext();) {
			IResource r = (IResource) i.next();
			if (!isAccessible(r)) {
				return false;
			}
		}
		return true;
	}
	/**
	 * Returns the elements that the action is to be performed on.
	 * By default return the selected resources.
	 *
	 * @return list of resource elements (element type: <code>IResource</code>)
	 */
	protected List getActionResources() {
		return getSelectedResources();
	}
}