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_ 216
