content/browser/renderer_data_memoizing_store.h

   1 // Copyright 2013 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_RENDERER_DATA_MEMOIZING_STORE_H_
   6 #define CONTENT_BROWSER_RENDERER_DATA_MEMOIZING_STORE_H_
   7
   8 #include <map>
   9
  10 #include "base/bind.h"
  11 #include "base/synchronization/lock.h"
  12 #include "content/public/browser/browser_thread.h"
  13 #include "content/public/browser/render_process_host.h"
  14 #include "content/public/browser/render_process_host_observer.h"
  15
  16 namespace content {
  17
  18 // RendererDataMemoizingStore is a thread-safe container that retains reference
  19 // counted objects that are associated with one or more render processes.
  20 // Objects are identified by an int and only a single reference to a given
  21 // object is retained. RendererDataMemoizingStore watches for render process
  22 // termination and releases objects that are no longer associated with any
  23 // render process.
  24 //
  25 // TODO(jcampan): Rather than watching for render process termination, we should
  26 //                instead be listening to events such as resource cached/
  27 //                removed from cache, and remove the items when we know they
  28 //                are not used anymore.
  29 template <typename T>
  30 class RendererDataMemoizingStore : public RenderProcessHostObserver {
  31  public:
  32   RendererDataMemoizingStore() : next_item_id_(1) {
  33   }
  34
  35   ~RendererDataMemoizingStore() {
  36     DCHECK_EQ(0U, id_to_item_.size()) << "Failed to outlive render processes";
  37   }
  38
  39   // Store adds |item| to this collection, associates it with the given render
  40   // process id and returns an opaque identifier for it. If |item| is already
  41   // known, the same identifier will be returned.
  42   int Store(T* item, int process_id) {
  43     DCHECK(item);
  44     base::AutoLock auto_lock(lock_);
  45
  46     int item_id;
  47
  48     // Do we already know this item?
  49     typename ReverseItemMap::iterator item_iter = item_to_id_.find(item);
  50     if (item_iter == item_to_id_.end()) {
  51       item_id = next_item_id_++;
  52       // We use 0 as an invalid item_id value.  In the unlikely event that
  53       // next_item_id_ wraps around, we reset it to 1.
  54       if (next_item_id_ == 0)
  55         next_item_id_ = 1;
  56       id_to_item_[item_id] = item;
  57       item_to_id_[item] = item_id;
  58     } else {
  59       item_id = item_iter->second;
  60     }
  61
  62     // Let's update process_id_to_item_id_.
  63     std::pair<IDMap::iterator, IDMap::iterator> process_ids =
  64         process_id_to_item_id_.equal_range(process_id);
  65     bool already_watching_process = (process_ids.first != process_ids.second);
  66     if (std::find_if(process_ids.first, process_ids.second,
  67                      MatchSecond<int>(item_id)) == process_ids.second) {
  68       process_id_to_item_id_.insert(std::make_pair(process_id, item_id));
  69     }
  70
  71     // And item_id_to_process_id_.
  72     std::pair<IDMap::iterator, IDMap::iterator> item_ids =
  73         item_id_to_process_id_.equal_range(item_id);
  74     if (std::find_if(item_ids.first, item_ids.second,
  75                      MatchSecond<int>(process_id)) == item_ids.second) {
  76       item_id_to_process_id_.insert(std::make_pair(item_id, process_id));
  77     }
  78
  79     // If we're not doing so already, keep an eye for the process host deletion.
  80     if (!already_watching_process) {
  81       if (BrowserThread::CurrentlyOn(BrowserThread::UI)) {
  82         StartObservingProcess(process_id);
  83       } else {
  84         BrowserThread::PostTask(
  85             BrowserThread::UI,
  86             FROM_HERE,
  87             base::Bind(&RendererDataMemoizingStore::StartObservingProcess,
  88                        base::Unretained(this),
  89                        process_id));
  90       }
  91     }
  92
  93     DCHECK(item_id);
  94     return item_id;
  95   }
  96
  97   // Retrieve fetches a previously Stored() item, identified by |item_id|.
  98   // If |item_id| is recognized, |item| will be updated and Retrieve() will
  99   // return true, it will otherwise return false.
 100   bool Retrieve(int item_id, scoped_refptr<T>* item) {
 101     base::AutoLock auto_lock(lock_);
 102
 103     typename ItemMap::iterator iter = id_to_item_.find(item_id);
 104     if (iter == id_to_item_.end())
 105       return false;
 106     if (item)
 107       *item = iter->second;
 108     return true;
 109   }
 110
 111  private:
 112   typedef std::multimap<int, int> IDMap;
 113   typedef std::map<int, scoped_refptr<T> > ItemMap;
 114   typedef std::map<T*, int, typename T::LessThan> ReverseItemMap;
 115
 116   template <typename M>
 117   struct MatchSecond {
 118     explicit MatchSecond(const M& t) : value(t) {}
 119
 120     template <typename Pair>
 121     bool operator()(const Pair& p) const {
 122       return (value == p.second);
 123     }
 124
 125     M value;
 126   };
 127
 128   void StartObservingProcess(int process_id) {
 129     DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 130     RenderProcessHost* host = RenderProcessHost::FromID(process_id);
 131     if (!host) {
 132       // We lost the race to observe the host before it was destroyed. Since
 133       // this function was called because we're managing objects tied to that
 134       // (now destroyed) RenderProcessHost, let's clean up.
 135       RemoveRenderProcessItems(process_id);
 136       return;
 137     }
 138
 139     host->AddObserver(this);
 140   }
 141
 142   // Remove the item specified by |item_id| from id_to_item_ and item_to_id_.
 143   // NOTE: the caller (RemoveRenderProcessItems) must hold lock_.
 144   void RemoveInternal(int item_id) {
 145     typename ItemMap::iterator item_iter = id_to_item_.find(item_id);
 146     DCHECK(item_iter != id_to_item_.end());
 147
 148     typename ReverseItemMap::iterator id_iter =
 149         item_to_id_.find(item_iter->second.get());
 150     DCHECK(id_iter != item_to_id_.end());
 151     item_to_id_.erase(id_iter);
 152
 153     id_to_item_.erase(item_iter);
 154   }
 155
 156   void RenderProcessHostDestroyed(RenderProcessHost* host) {
 157     DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 158     RemoveRenderProcessItems(host->GetID());
 159   }
 160
 161   // Removes all the items associated with the specified process from the store.
 162   void RemoveRenderProcessItems(int process_id) {
 163     base::AutoLock auto_lock(lock_);
 164
 165     // We iterate through all the item ids for that process.
 166     std::pair<IDMap::iterator, IDMap::iterator> process_ids =
 167         process_id_to_item_id_.equal_range(process_id);
 168     for (IDMap::iterator ids_iter = process_ids.first;
 169          ids_iter != process_ids.second; ++ids_iter) {
 170       int item_id = ids_iter->second;
 171       // Find all the processes referring to this item id in
 172       // item_id_to_process_id_, then locate the process being removed within
 173       // that range.
 174       std::pair<IDMap::iterator, IDMap::iterator> item_ids =
 175           item_id_to_process_id_.equal_range(item_id);
 176       IDMap::iterator proc_iter = std::find_if(
 177           item_ids.first, item_ids.second, MatchSecond<int>(process_id));
 178       DCHECK(proc_iter != item_ids.second);
 179
 180       // Before removing, determine if no other processes refer to the current
 181       // item id. If |proc_iter| (the current process) is the lower bound of
 182       // processes containing the current item id and if |next_proc_iter| is the
 183       // upper bound (the first process that does not), then only one process,
 184       // the one being removed, refers to the item id.
 185       IDMap::iterator next_proc_iter = proc_iter;
 186       ++next_proc_iter;
 187       bool last_process_for_item_id =
 188           (proc_iter == item_ids.first && next_proc_iter == item_ids.second);
 189       item_id_to_process_id_.erase(proc_iter);
 190
 191       if (last_process_for_item_id) {
 192         // The current item id is not referenced by any other processes, so
 193         // remove it from id_to_item_ and item_to_id_.
 194         RemoveInternal(item_id);
 195       }
 196     }
 197     if (process_ids.first != process_ids.second)
 198       process_id_to_item_id_.erase(process_ids.first, process_ids.second);
 199   }
 200
 201   IDMap process_id_to_item_id_;
 202   IDMap item_id_to_process_id_;
 203   ItemMap id_to_item_;
 204   ReverseItemMap item_to_id_;
 205
 206   int next_item_id_;
 207
 208   // This lock protects: process_id_to_item_id_, item_id_to_process_id_,
 209   //                     id_to_item_, and item_to_id_.
 210   base::Lock lock_;
 211 };
 212
 213 }  // namespace content
 214
 215 #endif  // CONTENT_BROWSER_RENDERER_DATA_MEMOIZING_STORE_H_