[Sync] Add logic to reassociate tab nodes after restart.

chrome/browser/sync/glue/tab_node_pool.h

Index: chrome/browser/sync/glue/tab_node_pool.h
diff --git a/chrome/browser/sync/glue/tab_node_pool.h b/chrome/browser/sync/glue/tab_node_pool.h
index 8327d061e08551ecf4fb835e39b06b80f1a613f5..4ad3fefd7fb63b162f486f3d29af379e86aaeb9a 100644
--- a/chrome/browser/sync/glue/tab_node_pool.h
+++ b/chrome/browser/sync/glue/tab_node_pool.h
@@ -5,10 +5,13 @@
 #ifndef CHROME_BROWSER_SYNC_GLUE_TAB_NODE_POOL_H_
 #define CHROME_BROWSER_SYNC_GLUE_TAB_NODE_POOL_H_
 
+#include <map>
+#include <set>
 #include <string>
-#include <vector>
 
 #include "base/basictypes.h"
+#include "base/gtest_prod_util.h"
+#include "chrome/browser/sessions/session_id.h"
 
 class ProfileSyncService;
 
@@ -16,77 +19,97 @@ namespace browser_sync {
 
 // A pool for managing free/used tab sync nodes. Performs lazy creation
 // of sync nodes when necessary.
+// Note: We make use of the following "id's"
+// - a sync_id: an int64 used in |syncer::InitByIdLookup|
+// - a tab_id: created by session service, unique to this client
+// - a tab_node_id: the id for a particular sync tab node. This is used
+//   to generate the sync tab node tag through:
+//       tab_tag = StringPrintf("%s_%ui", local_session_tag, tab_node_id);
+// tab_node_id and sync_id are both unique to a particular sync node. The
+// difference is that tab_node_id is controlled by the model associator and
+// is used when creating a new sync node, which returns the sync_id, created
+// by the sync db.
 class TabNodePool {
  public:
   explicit TabNodePool(ProfileSyncService* sync_service);
   ~TabNodePool();
-
+  enum InvalidTab {
+    kInvalidTabID = -1
+  };
   // Build a sync tag from tab_node_id.
   static std::string TabIdToTag(const std::string machine_tag,
                                 size_t tab_node_id);
 
-  // Add a previously allocated tab sync node to our pool. Increases the size
-  // of tab_syncid_pool_ by one and marks the new tab node as free.
+  // Returns the sync_id for the next free tab node. If none are available,
+  // creates a new tab node and adds it to free nodes pool. The free node can
+  // then be used to associate with a tab by calling AssociateTabNode.
+  // Note: The node is considered free until it has been associated. Repeated
+  // calls to GetFreeTabNode will return the same sync_id until node has been
+  // associated.
+  int64 GetFreeTabNode();
+
+  // Removes the node from |syncid_tabid_map_| and returns the node to free
+  // pool.
+  void FreeTabNode(int64 sync_id);
+
+  // Removes |sync_id| from free node pool and associates it with |tab_id|.
+  // sync_id should be id of a free node. In order to associate a non free
+  // sync node, use ReassociateTabNode.
+  void AssociateTabNode(int64 sync_id, SessionID::id_type tab_id);
+
+  // Associate sync_id with tab_id but does not add it to free node pool.
   // Note: this should only be called when we discover tab sync nodes from
   // previous sessions, not for freeing tab nodes we created through
   // GetFreeTabNode (use FreeTabNode below for that).
-  void AddTabNode(int64 sync_id);
+  // The difference between AddTabNode and AssociateTabNode is that
+  // AssociateTabNode requires the sync node to be free to be associated.
+  // AddTabNode just adds the association.
+  void AddTabNode(int64 sync_id, const SessionID& tab_id, size_t tab_node_id);
 
-  // Returns the sync_id for the next free tab node. If none are available,
-  // creates a new tab node.
-  // Note: We make use of the following "id's"
-  // - a sync_id: an int64 used in |syncer::InitByIdLookup|
-  // - a tab_id: created by session service, unique to this client
-  // - a tab_node_id: the id for a particular sync tab node. This is used
-  //   to generate the sync tab node tag through:
-  //       tab_tag = StringPrintf("%s_%ui", local_session_tag, tab_node_id);
-  // tab_node_id and sync_id are both unique to a particular sync node. The
-  // difference is that tab_node_id is controlled by the model associator and
-  // is used when creating a new sync node, which returns the sync_id, created
-  // by the sync db.
-  int64 GetFreeTabNode();
+  // Returns the tab_id for |sync_id| if it exists else returns kInvalidTabID.
+  SessionID::id_type GetTabIdFromSyncId(int64 sync_id) const;
 
-  // Return a tab node to our free pool.
-  // Note: the difference between FreeTabNode and AddTabNode is that
-  // FreeTabNode does not modify the size of |tab_syncid_pool_|, while
-  // AddTabNode increases it by one. In the case of FreeTabNode, the size of
-  // the |tab_syncid_pool_| should always be equal to the amount of tab nodes
-  // associated with this machine.
-  void FreeTabNode(int64 sync_id);
+  // Reassociates sync node with id |sync_id| with tab node with |tab_id|.
+  // Returns true if it is able to reassociate the node, false if a sync node
+  // with id |sync_id| is not associated with any tab.
+  bool ReassociateTabNode(int64 sync_id, SessionID::id_type tab_id);
+
+  // Returns any nodes with sync_ids not in |used_synced_ids| to free node pool.
+  void FreeUnusedTabNodes(const std::set<int64>& used_sync_ids);
 
   // Clear tab pool.
-  void clear() {
-    tab_syncid_pool_.clear();
-    tab_pool_fp_ = -1;
-  }
+  void Clear();
 
   // Return the number of tab nodes this client currently has allocated
   // (including both free and used nodes)
-  size_t capacity() const { return tab_syncid_pool_.size(); }
+  size_t Capacity() const;
 
   // Return empty status (all tab nodes are in use).
-  bool empty() const { return tab_pool_fp_ == -1; }
+  bool Empty() const;
 
   // Return full status (no tab nodes are in use).
-  bool full() {
-    return tab_pool_fp_ == static_cast<int64>(tab_syncid_pool_.size())-1;
-  }
+  bool Full();
 
-  void set_machine_tag(const std::string& machine_tag) {
-    machine_tag_ = machine_tag;
-  }
+  void SetMachineTag(const std::string& machine_tag);
 
  private:
-  // Pool of all available syncid's for tab's we have created.
-  std::vector<int64> tab_syncid_pool_;
+  friend class SyncTabNodePoolTest;
+  typedef std::map<int64, SessionID::id_type> SyncIDToTabIDMap;
+
+  // Stores mapping of sync_ids associated with tab_ids, these are the used
+  // nodes of tab node pool.
+  // The nodes in the map can be returned to free tab node pool by calling
+  // FreeTabNode(sync_id).
+  SyncIDToTabIDMap syncid_tabid_map_;
+
+  // The sync ids for the set of free sync nodes.
+  std::set<int64> free_nodes_pool_;
 
-  // Free pointer for tab pool. Only those node id's, up to and including the
-  // one indexed by the free pointer, are valid and free. The rest of the
-  // |tab_syncid_pool_| is invalid because the nodes are in use.
-  // To get the next free node, use tab_syncid_pool_[tab_pool_fp_--].
-  int64 tab_pool_fp_;
+  // The maximum used tab_node id for a sync node. A new sync node will always
+  // be created with max_used_tab_node_id_ + 1.
+  size_t max_used_tab_node_id_;
 
-  // The machiine tag associated with this tab pool. Used in the title of new
+  // The machine tag associated with this tab pool. Used in the title of new
   // sync nodes.
   std::string machine_tag_;