@Override
    public final boolean isClosed() {
        return closeable.isClosed();
    }
Begins the shutdown procedure by calling {@link #doStop(Object)}, ensuring that neither
{@link #doStart(Object)} nor {@link #doStop(Object)} is invoked concurrently.

@param arg the argument to pass to {@link #doStop(Object)}, or {@code null} to pass no argument.
core/src/main/java/com/linecorp/armeria/common/util/StartStopSupport.java