org.eclipse.swt.widgets.Control.requestLayout()

public void requestLayout () {
    getShell ().layout (new Control[] {this}, SWT.DEFER);
}

org.eclipse.swt.widgets.Composite.layout(Control[], int) code

public void layout (Control [] changed, int flags) {
    checkWidget ();
    if (changed != null) {
        for (Control control : changed) {
            if (control == null) error (SWT.ERROR_INVALID_ARGUMENT);
            if (control.isDisposed ()) error (SWT.ERROR_INVALID_ARGUMENT);
            boolean ancestor = false;
            Composite composite = control.parent;
            while (composite != null) {
                ancestor = composite == this;
                if (ancestor) break;
                composite = composite.parent;
            }
            if (!ancestor) error (SWT.ERROR_INVALID_PARENT);
        }
        int updateCount = 0;
        Composite [] update = new Composite [16];
        for (Control element : changed) {
            Control child = element;
            Composite composite = child.parent;
            // Update layout when the list of children has changed.
            // See bug 497812.
            child.markLayout(false, false);
            while (child != this) {
                if (composite.layout != null) {
                    composite.state |= LAYOUT_NEEDED;
                    if (!composite.layout.flushCache (child)) {
                        composite.state |= LAYOUT_CHANGED;
                    }
                }
                if (updateCount == update.length) {
                    Composite [] newUpdate = new Composite [update.length + 16];
                    System.arraycopy (update, 0, newUpdate, 0, update.length);
                    update = newUpdate;
                }
                child = update [updateCount++] = composite;
                composite = child.parent;
            }
        }
        if (!display.externalEventLoop && (flags & SWT.DEFER) != 0) {
            setLayoutDeferred (true);
            display.addLayoutDeferred (this);
        }
        // ① here! here! here!
        for (int i=updateCount-1; i>=0; i--) {
            update [i].updateLayout (false);
        }
    } else {
        if (layout == null && (flags & SWT.ALL) == 0) return;
        markLayout ((flags & SWT.CHANGED) != 0, (flags & SWT.ALL) != 0);
        if (!display.externalEventLoop && (flags & SWT.DEFER) != 0) {
            setLayoutDeferred (true);
            display.addLayoutDeferred (this);
        }
        updateLayout ((flags & SWT.ALL) != 0);
    }
}

In line ① , this control and all of its ancestors are laid out immediately , why does the documentation for Control.requestLayout() say that ‘The control will not be repositioned synchronously’ ?