Adding a previews IO-thread blacklist

components/previews/core/previews_black_list.h

+// Copyright 2016 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 COMPONENTS_PREVIEWS_CORE_PREVIEWS_BLACK_LIST_H_
+#define COMPONENTS_PREVIEWS_CORE_PREVIEWS_BLACK_LIST_H_
+
+#include <stdint.h>
+
+#include <memory>
+#include <queue>
+#include <string>
+#include <vector>
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "base/threading/thread_checker.h"
+#include "components/previews/core/previews_opt_out_store.h"
+
+class GURL;
+
+namespace base {
+class Clock;
+}
+
+namespace previews {
+class PreviewsBlackListItem;
+
+// Manages the state of black listed domains for the previews experiment. Loads
+// the stored black list from |opt_out_store| and manages an in memory black
+// list on the IO thread. Updates to the black list are stored in memory and
+// pushed to the store. Asynchronous modifications are stored in a queue and
+// executed in order. Reading from the black list is always synchronous, and if
+// the black list is not currently loaded (e.g., at startup, after clearing
+// browsing history), domains are reported as black listed. The list stores no
+// more than previews::params::MaxInMemoryHostsInBlackList hosts in-memory,
+// which defaults to 100.
+class PreviewsBlackList {
+ public:
+  // |opt_out_store| is the backing store to retrieve and store black list
+  // information, and can be null. When |opt_out_store| is null, the in-memory
+  // map will be immediately loaded to empty. If |opt_out_store| is non-null,
+  // it will be used to load the in-memory map asynchronously.
+  PreviewsBlackList(std::unique_ptr<PreviewsOptOutStore> opt_out_store,
+                    std::unique_ptr<base::Clock> clock);
+  ~PreviewsBlackList();
+
+  // Asynchronously adds a new navigation to to the in-memory black list and
+  // backing store. |opt_out| is whether the user opted out of the preview or
+  // navigated away from the page without opting out. |type| is only passed to
+  // the backing store. If the in memory map has reached the max number of hosts
+  // allowed, and |url| is a new host, a host will be evicted based on recency
+  // of the hosts most recent opt out.
+  void AddPreviewNavigation(const GURL& url, bool opt_out, PreviewsType type);
+
+  // Synchronously determines if |host_name| should be allowed to show previews.
+  // If the black list has loaded yet, this will always return false. |type| is
+  // not used to make this decision.
+  bool IsLoadedAndAllowed(const GURL& url, PreviewsType type) const;
+
+ private:
+  typedef base::Closure QueueClosure;

[tbansal1, 2016/09/22 21:12:27]

this typedef is confusing since it really does not have anything to do with
Queue by itself (except that it is stored in a queue at some point).
May be just remove the typedef?

[RyanSturm, 2016/09/23 17:23:24]

Done.

+
+  // Synchronous version of AddPreviewNavigation method.
+  void AddPreviewNavigationSync(const GURL& host_name,
+                                bool opt_out,
+                                PreviewsType type);
+
+  // Returns the PreviewsBlackListItem representing |host_name|. If there is no
+  // item for |host_name|, returns null.
+  PreviewsBlackListItem* GetBlackListItem(const std::string& host_name) const;
+
+  // Returns a new PreviewsBlackListItem representing |host_name|. Adds the new
+  // item to the in-memory map.
+  PreviewsBlackListItem* CreateBlackListItem(const std::string& host_name);
+
+  // Callback passed to the backing store when loading black list information.
+  // Moves the returned map into the in-memory black list and runs any
+  // outstanding tasks.
+  void LoadBlackListDone(std::unique_ptr<BlackListItemMap> black_list_item_map);
+
+  // Called while waiting for the black list to be loaded from the backing
+  // store.
+  // Enqueues a task to run when when loading black list information has
+  // completed. Maintains the order that tasks were called in.
+  void QueuePendingTask(QueueClosure callback);
+
+  // Evicts entries from the in-memory black list based on recency of a hosts

[tbansal1, 2016/09/22 21:12:27]

s/entries/one entry/
s/hosts/host's/

[RyanSturm, 2016/09/23 17:23:24]

Done.

+  // most recent opt out time.
+  void EvictOldestOptOut();
+
+  // Map maintaining the in-memory black list.
+  std::unique_ptr<BlackListItemMap> black_list_item_map_;
+
+  // Whether the black list is done being loaded from the backing store.
+  bool loaded_;
+
+  // The backing store of the black list information.
+  std::unique_ptr<PreviewsOptOutStore> opt_out_store_;
+
+  // Callbacks to be run after loading information from the backing store has
+  // completed.
+  std::queue<QueueClosure> pending_callbacks_;
+
+  std::unique_ptr<base::Clock> clock_;
+
+  base::ThreadChecker thread_checker_;
+
+  base::WeakPtrFactory<PreviewsBlackList> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(PreviewsBlackList);
+};
+
+}  // namespace previews
+
+#endif  // COMPONENTS_PREVIEWS_CORE_PREVIEWS_BLACK_LIST_H_