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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef CONTENT_BROWSER_LOADER_RESOURCE_SCHEDULER_H_
      6 #define CONTENT_BROWSER_LOADER_RESOURCE_SCHEDULER_H_
      7 
      8 #include <map>
      9 #include <set>
     10 
     11 #include "base/basictypes.h"
     12 #include "base/compiler_specific.h"
     13 #include "base/memory/scoped_ptr.h"
     14 #include "base/threading/non_thread_safe.h"
     15 #include "content/common/content_export.h"
     16 #include "net/base/priority_queue.h"
     17 #include "net/base/request_priority.h"
     18 
     19 namespace net {
     20 class URLRequest;
     21 }
     22 
     23 namespace content {
     24 class ResourceThrottle;
     25 
     26 // There is one ResourceScheduler. All renderer-initiated HTTP requests are
     27 // expected to pass through it.
     28 //
     29 // There are two types of input to the scheduler:
     30 // 1. Requests to start, cancel, or finish fetching a resource.
     31 // 2. Notifications for renderer events, such as new tabs, navigation and
     32 //    painting.
     33 //
     34 // These input come from different threads, so they may not be in sync. The UI
     35 // thread is considered the authority on renderer lifetime, which means some
     36 // IPCs may be meaningless if they arrive after the UI thread signals a renderer
     37 // has been deleted.
     38 //
     39 // The ResourceScheduler tracks many Clients, which should correlate with tabs.
     40 // A client is uniquely identified by its child_id and route_id.
     41 //
     42 // Each Client may have many Requests in flight. Requests are uniquely
     43 // identified within a Client by its ScheduledResourceRequest.
     44 //
     45 // Users should call ScheduleRequest() to notify this ResourceScheduler of a
     46 // new request. The returned ResourceThrottle should be destroyed when the load
     47 // finishes or is canceled.
     48 //
     49 // The scheduler may defer issuing the request via the ResourceThrottle
     50 // interface or it may alter the request's priority by calling set_priority() on
     51 // the URLRequest.
     52 class CONTENT_EXPORT ResourceScheduler : public base::NonThreadSafe {
     53  public:
     54   ResourceScheduler();
     55   ~ResourceScheduler();
     56 
     57   // Requests that this ResourceScheduler schedule, and eventually loads, the
     58   // specified |url_request|. Caller should delete the returned ResourceThrottle
     59   // when the load completes or is canceled.
     60   scoped_ptr<ResourceThrottle> ScheduleRequest(
     61       int child_id, int route_id, net::URLRequest* url_request);
     62 
     63   // Signals from the UI thread, posted as tasks on the IO thread:
     64 
     65   // Called when a renderer is created.
     66   void OnClientCreated(int child_id, int route_id);
     67 
     68   // Called when a renderer is destroyed.
     69   void OnClientDeleted(int child_id, int route_id);
     70 
     71   // Signals from IPC messages directly from the renderers:
     72 
     73   // Called when a client navigates to a new main document.
     74   void OnNavigate(int child_id, int route_id);
     75 
     76   // Called when the client has parsed the <body> element. This is a signal that
     77   // resource loads won't interfere with first paint.
     78   void OnWillInsertBody(int child_id, int route_id);
     79 
     80  private:
     81   class RequestQueue;
     82   class ScheduledResourceRequest;
     83   struct Client;
     84 
     85   typedef int64 ClientId;
     86   typedef std::map<ClientId, Client*> ClientMap;
     87   typedef std::set<ScheduledResourceRequest*> RequestSet;
     88 
     89   // Called when a ScheduledResourceRequest is destroyed.
     90   void RemoveRequest(ScheduledResourceRequest* request);
     91 
     92   // Unthrottles the |request| and adds it to |client|.
     93   void StartRequest(ScheduledResourceRequest* request, Client* client);
     94 
     95   // Update the queue position for |request|, possibly causing it to start
     96   // loading.
     97   //
     98   // Queues are maintained for each priority level. When |request| is
     99   // reprioritized, it will move to the end of the queue for that priority
    100   // level.
    101   void ReprioritizeRequest(ScheduledResourceRequest* request,
    102                            net::RequestPriority new_priority);
    103 
    104   // Attempts to load any pending requests in |client|, based on the
    105   // results of ShouldStartRequest().
    106   void LoadAnyStartablePendingRequests(Client* client);
    107 
    108   // Returns the number of requests with priority < LOW that are currently in
    109   // flight.
    110   size_t GetNumDelayableRequestsInFlight(Client* client) const;
    111 
    112   // Returns true if the request should start. This is the core scheduling
    113   // algorithm.
    114   bool ShouldStartRequest(ScheduledResourceRequest* request,
    115                           Client* client) const;
    116 
    117   // Returns the client ID for the given |child_id| and |route_id| combo.
    118   ClientId MakeClientId(int child_id, int route_id);
    119 
    120   ClientMap client_map_;
    121   RequestSet unowned_requests_;
    122 };
    123 
    124 }  // namespace content
    125 
    126 #endif  // CONTENT_BROWSER_LOADER_RESOURCE_SCHEDULER_H_
    127