private void cancelFutures() {
        if (shutdownFuture != null) {
            shutdownFuture.cancel(false);
            shutdownFuture = null;
        }
        if (pingWriteFuture != null) {
            pingWriteFuture.cancel(false);
            pingWriteFuture = null;
        }
    }
An {@link AbstractKeepAliveHandler} that writes a PING when neither read nor write was performed for
the specified {@code pingIntervalMillis}, and closes the connection
when neither read nor write was performed within the given {@code idleTimeoutMillis}.
core/src/main/java/com/linecorp/armeria/internal/common/AbstractKeepAliveHandler.java