extensions/browser/updater/request_queue.h

   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 EXTENSIONS_BROWSER_UPDATER_REQUEST_QUEUE_H_
   6 #define EXTENSIONS_BROWSER_UPDATER_REQUEST_QUEUE_H_
   7
   8 #include <deque>
   9 #include <utility>
  10
  11 #include "base/callback.h"
  12 #include "base/memory/linked_ptr.h"
  13 #include "base/memory/scoped_ptr.h"
  14 #include "base/time/time.h"
  15 #include "base/timer/timer.h"
  16 #include "net/base/backoff_entry.h"
  17
  18 namespace extensions {
  19
  20 // This class keeps track of a queue of requests, and contains the logic to
  21 // retry requests with some backoff policy. Each request has a
  22 // net::BackoffEntry instance associated with it.
  23 //
  24 // The general flow when using this class would be something like this:
  25 //   - requests are queued up by calling ScheduleRequest.
  26 //   - when a request is ready to be executed, RequestQueue removes the
  27 //     request from the queue, assigns it as active request, and calls
  28 //     the callback that was passed to the constructor.
  29 //   - (optionally) when a request has completed unsuccessfully call
  30 //     RetryRequest to put the request back in the queue, using the
  31 //     backoff policy and minimum backoff delay to determine when to
  32 //     next schedule this request.
  33 //   - call reset_active_request() to indicate that the active request has
  34 //     been dealt with.
  35 //   - call StartNextRequest to schedule the next pending request (if any).
  36 template <typename T>
  37 class RequestQueue {
  38  public:
  39   class iterator;
  40
  41   RequestQueue(const net::BackoffEntry::Policy* backoff_policy,
  42                const base::Closure& start_request_callback);
  43   ~RequestQueue();
  44
  45   // Returns the request that is currently being processed.
  46   T* active_request();
  47
  48   // Returns the number of times the current request has been retried already.
  49   int active_request_failure_count();
  50
  51   // Signals RequestQueue that processing of the current request has completed.
  52   scoped_ptr<T> reset_active_request();
  53
  54   // Add the given request to the queue, and starts the next request if no
  55   // request is currently being processed.
  56   void ScheduleRequest(scoped_ptr<T> request);
  57
  58   bool empty() const;
  59   size_t size() const;
  60
  61   // Returns the earliest release time of all requests currently in the queue.
  62   base::TimeTicks NextReleaseTime() const;
  63
  64   // Starts the next request, if no request is currently active. This will
  65   // synchronously call the start_request_callback if the release time of the
  66   // earliest available request is in the past, otherwise it will call that
  67   // callback asynchronously after enough time has passed.
  68   void StartNextRequest();
  69
  70   // Tell RequestQueue to put the current request back in the queue, after
  71   // applying the backoff policy to determine when to next try this request.
  72   // If the policy results in a backoff delay smaller than |min_backoff_delay|,
  73   // that delay is used instead.
  74   void RetryRequest(const base::TimeDelta& min_backoff_delay);
  75
  76   iterator begin();
  77   iterator end();
  78
  79   // Change the backoff policy used by the queue.
  80   void set_backoff_policy(const net::BackoffEntry::Policy* backoff_policy);
  81
  82  private:
  83   struct Request {
  84     Request(net::BackoffEntry* backoff_entry, T* request)
  85         : backoff_entry(backoff_entry), request(request) {}
  86     linked_ptr<net::BackoffEntry> backoff_entry;
  87     linked_ptr<T> request;
  88   };
  89
  90   // Compares the release time of two pending requests.
  91   static bool CompareRequests(const Request& a, const Request& b);
  92
  93   // Pushes a request with a given backoff entry onto the queue.
  94   void PushImpl(scoped_ptr<T> request,
  95                 scoped_ptr<net::BackoffEntry> backoff_entry);
  96
  97   // The backoff policy used to determine backoff delays.
  98   const net::BackoffEntry::Policy* backoff_policy_;
  99
 100   // Callback to call when a new request has become the active request.
 101   base::Closure start_request_callback_;
 102
 103   // Priority queue of pending requests. Not using std::priority_queue since
 104   // the code needs to be able to iterate over all pending requests.
 105   std::deque<Request> pending_requests_;
 106
 107   // Active request and its associated backoff entry.
 108   scoped_ptr<T> active_request_;
 109   scoped_ptr<net::BackoffEntry> active_backoff_entry_;
 110
 111   // Timer to schedule calls to StartNextRequest, if the first pending request
 112   // hasn't passed its release time yet.
 113   base::Timer timer_;
 114 };
 115
 116 // Iterator class that wraps a std::deque<> iterator, only giving access to the
 117 // actual request part of each item.
 118 template <typename T>
 119 class RequestQueue<T>::iterator {
 120  public:
 121   iterator() {}
 122
 123   T* operator*() { return it_->request.get(); }
 124   T* operator->() { return it_->request.get(); }
 125   iterator& operator++() {
 126     ++it_;
 127     return *this;
 128   }
 129   bool operator!=(const iterator& b) const { return it_ != b.it_; }
 130
 131  private:
 132   friend class RequestQueue<T>;
 133   typedef std::deque<typename RequestQueue<T>::Request> Container;
 134
 135   explicit iterator(const typename Container::iterator& it) : it_(it) {}
 136
 137   typename Container::iterator it_;
 138 };
 139
 140 }  // namespace extensions
 141
 142 #endif  // EXTENSIONS_BROWSER_UPDATER_REQUEST_QUEUE_H_