Adds speculative prefetching of resources.

chrome/browser/predictors/resource_prefetcher.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_PREDICTORS_RESOURCE_PREFETCHER_H_
+#define CHROME_BROWSER_PREDICTORS_RESOURCE_PREFETCHER_H_
+
+#include <map>
+#include <list>
+#include <vector>
+
+#include "base/memory/linked_ptr.h"
+#include "base/threading/non_thread_safe.h"
+#include "chrome/browser/predictors/resource_prefetch_common.h"
+#include "googleurl/src/gurl.h"
+#include "net/url_request/url_request.h"
+
+namespace net {
+class URLRequestContext;
+}
+
+namespace predictors {
+
+// Responsible for prefetching resources for a single navigation based on the
+// input list of resources.
+//  - Limits the max number of resources in flight for any host and also across
+//    hosts.
+//  - When stopped, will wait for the pending requests to finish.
+//  - Lives entirely on the IO thread.
+class ResourcePrefetcher : public base::NonThreadSafe,
+                           public net::URLRequest::Delegate {
+ public:
+  // Denotes the prefetch request for a single subresource.
+  struct Request {
+    explicit Request(const GURL& i_resource_url);
+    Request(const Request& other);
+
+    enum PrefetchStatus {
+      PREFETCH_STATUS_NOT_STARTED,
+      PREFETCH_STATUS_STARTED,
+      PREFETCH_STATUS_CANCELLED,
+      PREFETCH_STATUS_FAILED,
+      PREFETCH_STATUS_FROM_CACHE,
+      PREFETCH_STATUS_FROM_NETWORK
+    };
+
+    enum UsageStatus {
+      USAGE_STATUS_NOT_REQUESTED,
+      USAGE_STATUS_FROM_CACHE,
+      USAGE_STATUS_FROM_NETWORK,
+      USAGE_STATUS_NAVIGATION_ABANDONED
+    };
+
+    GURL resource_url;
+    PrefetchStatus prefetch_status;
+    UsageStatus usage_status;
+  };
+  typedef std::vector<linked_ptr<Request> > RequestVector;

[dominich, 2012/07/23 16:04:41]

This being public makes it more difficult, but I think using a ScopedVector here
would be better. It would mean the Requests would stick around until the whole
RequestVector is deleted, but they aren't long lived, right?

[Shishir, 2012/08/01 22:35:24]

Changed to ScopedVector.

+
+  // Used to communicate when the prefetching is done. All methods are invoked
+  // on the IO thread.
+  class Delegate {
+   public:
+    virtual ~Delegate() { }
+
+    // Called when the ResourcePrefetcher is finished, i.e. there is nothing
+    // pending in flight.
+    virtual void ResourcePrefetcherFinished(
+        ResourcePrefetcher* prefetcher,
+        scoped_ptr<RequestVector> requests) = 0;
+
+    virtual net::URLRequestContext* GetURLRequestContext() = 0;
+  };
+
+  // 'delegate' has to outlive the ResourcePrefetcher.
+  ResourcePrefetcher(Delegate* delegate,

[dominich, 2012/07/23 16:04:41]

I think this should be an explicit dependency rather than a Delegate.

[dominich, 2012/07/23 16:04:41]

comment that this takes ownership of requests.

[Shishir, 2012/08/01 22:35:24]

Done.

[Shishir, 2012/08/01 22:35:24]

Done.

+                     const ResourcePrefetchPredictorConfig& config,
+                     const NavigationID& navigation_id,
+                     scoped_ptr<RequestVector> requests);
+  virtual ~ResourcePrefetcher();
+
+  void Start();  // Kicks off the prefetching. Can only be called once.
+  void Stop();   // No additional prefetches will be queued after this.
+
+  const NavigationID& navigation_id() const {
+    return navigation_id_;
+  }
+
+ private:
+  // Launches new prefetch requests if possible.
+  void TryToLaunchPrefetchRequests();
+
+  // Starts a net::URLRequest for the input 'request'.
+  void SendRequest(Request* request);
+
+  // Marks the request as finished, with the given status.
+  void FinishRequest(net::URLRequest* request, Request::PrefetchStatus status);
+
+  // Reads the response data from the response - required for the resource to
+  // be cached correctly.
+  void ReadFullResponse(net::URLRequest* request);
+
+  // net::URLRequest::Delegate methods.
+  virtual void OnReceivedRedirect(net::URLRequest* request,
+                                  const GURL& new_url,
+                                  bool* defer_redirect) OVERRIDE;
+  virtual void OnAuthRequired(net::URLRequest* request,
+                              net::AuthChallengeInfo* auth_info) OVERRIDE;
+  virtual void OnCertificateRequested(
+      net::URLRequest* request,
+      net::SSLCertRequestInfo* cert_request_info) OVERRIDE;
+  virtual void OnSSLCertificateError(net::URLRequest* request,
+                                     const net::SSLInfo& ssl_info,
+                                     bool fatal) OVERRIDE;
+  virtual void OnResponseStarted(net::URLRequest* request) OVERRIDE;
+  virtual void OnReadCompleted(net::URLRequest* request,
+                               int bytes_read) OVERRIDE;
+
+  enum PrefetcherState {
+    INITIALIZED = 0,  // Prefetching hasn't started.
+    RUNNING = 1,      // Prefetching started, allowed to add more requests.
+    STOPPED = 2,      // Prefetching started, not allowed to add more requests.
+    FINISHED = 3      // No more inflight request, new requests not possible.
+  };
+
+  PrefetcherState state_;
+  Delegate* const delegate_;
+  ResourcePrefetchPredictorConfig config_;
+  NavigationID navigation_id_;
+  scoped_ptr<RequestVector> request_vector_;
+
+  std::map<net::URLRequest*, Request*> inflight_requests_;
+  std::list<Request*> request_queue_;
+  std::map<std::string, int> host_inflight_counts_;
+
+  DISALLOW_COPY_AND_ASSIGN(ResourcePrefetcher);
+};
+
+}  // namespace predictors
+
+#endif  // CHROME_BROWSER_PREDICTORS_RESOURCE_PREFETCHER_H_