@Override
    public ClassicHttpResponse execute(
            final ClassicHttpRequest request,
            final ExecChain.Scope scope,
            final ExecChain chain) throws IOException, HttpException {
        Args.notNull(request, "HTTP request");
        Args.notNull(scope, "Scope");
        final HttpRoute route = scope.route;

        final ClassicHttpResponse response;
        try {
            response = chain.proceed(request, scope);
        } catch (final IOException | HttpException ex) {
            if (this.connectionBackoffStrategy.shouldBackoff(ex)) {
                if (LOG.isDebugEnabled()) {
                    LOG.debug("Backing off route {} due to exception: {}", route, ex.getMessage());
                }
                this.backoffManager.backOff(route);
            }
            throw ex;
        }
        if (this.connectionBackoffStrategy.shouldBackoff(response)) {
            if (LOG.isDebugEnabled()) {
                LOG.debug("Backing off route {} due to response status: {}", route, response.getCode());
            }
            this.backoffManager.backOff(route);
        } else {
            if (LOG.isDebugEnabled()) {
                LOG.debug("Probing route: {}", route);
            }
            this.backoffManager.probe(route);
        }
        return response;
    }
Constructs a {@code BackoffStrategyExec} with the specified
{@link ConnectionBackoffStrategy} and {@link BackoffManager}.

@param connectionBackoffStrategy the strategy to determine whether
                                 to backoff based on the response or exception
@param backoffManager            the manager responsible for applying backoff
                                 and probing actions to the HTTP routes
httpclient5/src/main/java/org/apache/hc/client5/http/impl/classic/BackoffStrategyExec.java