@Override
    public boolean cancel(boolean mayInterruptIfRunning) {
        final boolean updated = !isDone() && completeExceptionally(new CancellationException());
        return updated || isCancelled();
    }
An {@link RpcResponse} implementation which is initially incomplete and can be completed later.
core/src/main/java/com/linecorp/armeria/common/CompletableRpcResponse.java