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
* Note that this hook method is invoked in a non-UI thread.
	 * </p>
	 * <p>
	 * Subclasses must implement this method.
	 * </p>
	 *
	 * @return the message
	 */
	abstract String getOperationMessage();
	/**
	 * Returns the string to display for this action's problems dialog.
	 * <p>
	 * The <code>WorkspaceAction</code> implementation of this method returns a
	 * vague message (localized counterpart of something like "The following 
	 * problems occurred."). Subclasses may reimplement to provide something more
	 * suited to the particular action.
	 * </p>
	 *
	 * @return the problems message
	 */
	String getProblemsMessage() {
		return IDEWorkbenchMessages.getString("WorkbenchAction.problemsMessage"); 
	}
	/**
	 * Returns the title for this action's problems dialog.
	 * <p>
	 * The <code>WorkspaceAction</code> implementation of this method returns a
	 * generic title (localized counterpart of "Problems"). Subclasses may 
	 * reimplement to provide something more suited to the particular action.
	 * </p>