#vulnerable code 
                                CloseableHttpResponse handleBackendResponse(
            final HttpRoute route,
            final HttpRequestWrapper request,
            final HttpClientContext context,
            final HttpExecutionAware execAware,
            final Date requestDate,
            final Date responseDate,
            final CloseableHttpResponse backendResponse) throws IOException {

        log.trace("Handling Backend response");
        responseCompliance.ensureProtocolCompliance(request, backendResponse);

        final HttpHost target = route.getTargetHost();
        final boolean cacheable = responseCachingPolicy.isResponseCacheable(request, backendResponse);
        responseCache.flushInvalidatedCacheEntriesFor(target, request, backendResponse);
        if (cacheable && !alreadyHaveNewerCacheEntry(target, request, backendResponse)) {
            try {
                storeRequestIfModifiedSinceFor304Response(request, backendResponse);
                return Proxies.enhanceResponse(responseCache.cacheAndReturnResponse(
                        target, request, backendResponse, requestDate, responseDate));
            } finally {
                backendResponse.close();
            }
        }
        if (!cacheable) {
            try {
                responseCache.flushCacheEntriesFor(target, request);
            } catch (final IOException ioe) {
                log.warn("Unable to flush invalid cache entries", ioe);
            }
        }
        return backendResponse;
    } 
                            #location 22 
                            #vulnerability type INTERFACE_NOT_THREAD_SAFE
#fixed code
                                CachingExec(
            final ClientExecChain backend,
            final HttpCache responseCache,
            final CacheValidityPolicy validityPolicy,
            final ResponseCachingPolicy responseCachingPolicy,
            final CachedHttpResponseGenerator responseGenerator,
            final CacheableRequestPolicy cacheableRequestPolicy,
            final CachedResponseSuitabilityChecker suitabilityChecker,
            final ConditionalRequestBuilder conditionalRequestBuilder,
            final ResponseProtocolCompliance responseCompliance,
            final RequestProtocolCompliance requestCompliance,
            final CacheConfig config,
            final AsynchronousValidator asynchRevalidator) {
        this.cacheConfig = config != null ? config : CacheConfig.DEFAULT;
        this.backend = backend;
        this.responseCache = responseCache;
        this.validityPolicy = validityPolicy;
        this.responseCachingPolicy = responseCachingPolicy;
        this.responseGenerator = responseGenerator;
        this.cacheableRequestPolicy = cacheableRequestPolicy;
        this.suitabilityChecker = suitabilityChecker;
        this.conditionalRequestBuilder = conditionalRequestBuilder;
        this.responseCompliance = responseCompliance;
        this.requestCompliance = requestCompliance;
        this.asynchRevalidator = asynchRevalidator;
    }