@Override
  public void run() {
    Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
    Request<?> request;
    while (true) {
      try {
        // Take a request from the queue.
        request = mQueue.take();
      } catch (InterruptedException e) {
        // We may have been interrupted because it was time to quit.
        if (mQuit) {
          return;
        }
        continue;
      }

      try {
        request.addMarker("network-queue-take");

        // If the request was cancelled already, do not perform the
        // network request.
        if (request.isCanceled()) {
          request.finish("network-discard-cancelled");
          continue;
        }

        addTrafficStatsTag(request);

        // Perform the network request.
        NetworkResponse networkResponse = mNetwork.performRequest(request);
        request.addMarker("network-http-complete");

        // If the server returned 304 AND we delivered a response already,
        // we're done -- don't deliver a second identical response.
        if (networkResponse.notModified && request.hasHadResponseDelivered()) {
          request.finish("not-modified");
          continue;
        }

        // Parse the response here on the worker thread.
        Response<?> response = request.parseNetworkResponse(networkResponse);
        request.addMarker("network-parse-complete");

        // Write to cache if applicable.
        // TODO: Only update cache metadata instead of entire record for 304s.
        if (request.shouldCache() && response.cacheEntry != null) {
          mCache.put(request.getCacheKey(), response.cacheEntry);
          request.addMarker("network-cache-written");
        }

        // Post the response back.
        request.markDelivered();
        mDelivery.postResponse(request, response);
      } catch (VolleyError volleyError) {
        parseAndDeliverNetworkError(request, volleyError);
      } catch (Exception e) {
        VolleyLog.e(e, "Unhandled exception %s", e.toString());
        mDelivery.postError(request, new VolleyError(e));
      }
    }
  }
  @Override
  public void run() {
    if (DEBUG) {
      VolleyLog.v("start new dispatcher");
    }
    Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
    // Make a blocking call to initialize the cache.
    mCache.initialize();
    while (true) {
      try {
        // Get a request from the cache triage queue, blocking until at least one is available.
        final Request<?> request = mCacheQueue.take();
        request.addMarker("cache-queue-take");
        // If the request has been canceled, don't bother dispatching it.
        if (request.isCanceled()) {
          request.finish("cache-discard-canceled");
          continue;
        }

        // Attempt to retrieve this item from cache.
        Cache.Entry entry = mCache.get(request.getCacheKey());
        if (entry == null) {
          request.addMarker("cache-miss");
          // Cache miss; send off to the network dispatcher.
          mNetworkQueue.put(request);
          continue;
        }

        // If it is completely expired, just send it to the network.
        if (entry.isExpired()) {
          request.addMarker("cache-hit-expired");
          request.setCacheEntry(entry);
          mNetworkQueue.put(request);
          continue;
        }

        // We have a cache hit; parse its data for delivery back to the request.
        request.addMarker("cache-hit");
        Response<?> response =
            request.parseNetworkResponse(
                new NetworkResponse(entry.data, entry.responseHeaders)); // TODO
        request.addMarker("cache-hit-parsed");

        if (!entry.refreshNeeded()) {
          // Completely unexpired cache hit. Just deliver the response.
          mDelivery.postResponse(request, response);
        } else {
          // Soft-expired cache hit. We can deliver the cached response,
          // but we need to also send the request to the network for
          // refreshing.
          request.addMarker("cache-hit-refresh-needed");
          request.setCacheEntry(entry);

          // Mark the response as intermediate.
          response.intermediate = true;

          // Post the intermediate response back to the user and have
          // the delivery then forward the request along to the network.
          mDelivery.postResponse(
              request,
              response,
              new Runnable() {
                @Override
                public void run() {
                  try {
                    mNetworkQueue.put(request);
                  } catch (InterruptedException e) {
                    // Not much we can do about this.
                  }
                }
              });
        }

      } catch (InterruptedException e) {
        // We may have been interrupted because it was time to quit.
        if (mQuit) {
          return;
        }
        continue;
      }
    }
  }
 private void parseAndDeliverNetworkError(Request<?> request, VolleyError error) {
   error = request.parseNetworkError(error);
   mDelivery.postError(request, error);
 }