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      1 // Copyright 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 #include "sync/engine/update_applicator.h"
      6 
      7 #include <vector>
      8 
      9 #include "base/logging.h"
     10 #include "sync/engine/syncer_util.h"
     11 #include "sync/syncable/entry.h"
     12 #include "sync/syncable/mutable_entry.h"
     13 #include "sync/syncable/syncable_id.h"
     14 #include "sync/syncable/syncable_write_transaction.h"
     15 
     16 using std::vector;
     17 
     18 namespace syncer {
     19 
     20 using syncable::ID;
     21 
     22 UpdateApplicator::UpdateApplicator(Cryptographer* cryptographer)
     23     : cryptographer_(cryptographer),
     24       updates_applied_(0),
     25       encryption_conflicts_(0),
     26       hierarchy_conflicts_(0) {
     27 }
     28 
     29 UpdateApplicator::~UpdateApplicator() {
     30 }
     31 
     32 // Attempt to apply all updates, using multiple passes if necessary.
     33 //
     34 // Some updates must be applied in order.  For example, children must be created
     35 // after their parent folder is created.  This function runs an O(n^2) algorithm
     36 // that will keep trying until there is nothing left to apply, or it stops
     37 // making progress, which would indicate that the hierarchy is invalid.
     38 //
     39 // The update applicator also has to deal with simple conflicts, which occur
     40 // when an item is modified on both the server and the local model.  We remember
     41 // their IDs so they can be passed to the conflict resolver after all the other
     42 // applications are complete.
     43 //
     44 // Finally, there are encryption conflicts, which can occur when we don't have
     45 // access to all the Nigori keys.  There's nothing we can do about them here.
     46 void UpdateApplicator::AttemptApplications(
     47     syncable::WriteTransaction* trans,
     48     const std::vector<int64>& handles) {
     49   std::vector<int64> to_apply = handles;
     50 
     51   DVLOG(1) << "UpdateApplicator running over " << to_apply.size() << " items.";
     52   while (!to_apply.empty()) {
     53     std::vector<int64> to_reapply;
     54 
     55     for (std::vector<int64>::iterator i = to_apply.begin();
     56          i != to_apply.end(); ++i) {
     57       syncable::MutableEntry entry(trans, syncable::GET_BY_HANDLE, *i);
     58       UpdateAttemptResponse result = AttemptToUpdateEntry(
     59           trans, &entry, cryptographer_);
     60 
     61       switch (result) {
     62         case SUCCESS:
     63           updates_applied_++;
     64           break;
     65         case CONFLICT_SIMPLE:
     66           simple_conflict_ids_.insert(entry.GetId());
     67           break;
     68         case CONFLICT_ENCRYPTION:
     69           encryption_conflicts_++;
     70           break;
     71         case CONFLICT_HIERARCHY:
     72           // The decision to classify these as hierarchy conflcits is tentative.
     73           // If we make any progress this round, we'll clear the hierarchy
     74           // conflict count and attempt to reapply these updates.
     75           to_reapply.push_back(*i);
     76           break;
     77         default:
     78           NOTREACHED();
     79           break;
     80       }
     81     }
     82 
     83     if (to_reapply.size() == to_apply.size()) {
     84       // We made no progress.  Must be stubborn hierarchy conflicts.
     85       hierarchy_conflicts_ = to_apply.size();
     86       break;
     87     }
     88 
     89     // We made some progress, so prepare for what might be another iteration.
     90     // If everything went well, to_reapply will be empty and we'll break out on
     91     // the while condition.
     92     to_apply.swap(to_reapply);
     93     to_reapply.clear();
     94   }
     95 }
     96 
     97 }  // namespace syncer
     98