@Override
    public void postFrame(FrameBuffer out) {
        if (!isEnabled()) {
            return;
        }

        final AWTComponentRenderer frameTransfer = getFrameTransfer();
        if (frameTransfer != null) {
            frameTransfer.copyFrameBufferToImage(getRenderManager());
        }

        // for the next frame
        if (hasDestination() && reshapeNeeded.get() > 0 && reshapeNeeded.decrementAndGet() >= 0) {

            if (frameTransfer != null) {
                frameTransfer.dispose();
            }

            setFrameTransfer(reshapeInThread(askWidth, askHeight, askFixAspect));
        }
    }
The flag is true if this processor is main.
jme3-desktop/src/main/java/com/jme3/system/AWTFrameProcessor.java