From f175b4561cecb41a63fa2c35a35d05c59cd26c88 Mon Sep 17 00:00:00 2001
From: theoreticalbts <theoreticalbts@users.noreply.github.com>
Date: Mon, 6 Jul 2015 14:35:59 -0400
Subject: [PATCH] Properly re-initialize witness scheduler state after a long
 block gap

---
 libraries/chain/db_witness_schedule.cpp       | 22 ++++++++----
 .../graphene/chain/witness_scheduler.hpp      | 34 +++++++++++++++++++
 2 files changed, 50 insertions(+), 6 deletions(-)

diff --git a/libraries/chain/db_witness_schedule.cpp b/libraries/chain/db_witness_schedule.cpp
index 5095ac1b..a6d82bf6 100644
--- a/libraries/chain/db_witness_schedule.cpp
+++ b/libraries/chain/db_witness_schedule.cpp
@@ -106,6 +106,8 @@ void database::update_witness_schedule(signed_block next_block)
    // triggering FC_ASSERT elsewhere
 
    assert( schedule_slot > 0 );
+   witness_id_type first_witness;
+   bool slot_is_near = wso.scheduler.get_slot( schedule_slot-1, first_witness );
 
    witness_id_type wit;
 
@@ -119,13 +121,21 @@ void database::update_witness_schedule(signed_block next_block)
       witness_scheduler_rng rng(wso.rng_seed.data, _wso.slots_since_genesis);
 
       _wso.scheduler._min_token_count = std::max(int(gpo.active_witnesses.size()) / 2, 1);
-      uint32_t drain = schedule_slot;
-      while( drain > 0 )
+
+      if( slot_is_near )
       {
-         if( _wso.scheduler.size() == 0 )
-            break;
-         _wso.scheduler.consume_schedule();
-         --drain;
+         uint32_t drain = schedule_slot;
+         while( drain > 0 )
+         {
+            if( _wso.scheduler.size() == 0 )
+               break;
+            _wso.scheduler.consume_schedule();
+            --drain;
+         }
+      }
+      else
+      {
+         _wso.scheduler.reset_schedule( first_witness );
       }
       while( !_wso.scheduler.get_slot(schedule_needs_filled, wit) )
       {
diff --git a/libraries/chain/include/graphene/chain/witness_scheduler.hpp b/libraries/chain/include/graphene/chain/witness_scheduler.hpp
index 77f67478..ec595922 100644
--- a/libraries/chain/include/graphene/chain/witness_scheduler.hpp
+++ b/libraries/chain/include/graphene/chain/witness_scheduler.hpp
@@ -313,6 +313,40 @@ class generic_witness_scheduler
          return true;
       }
 
+      /**
+       * Reset the schedule, then re-schedule the given witness as the
+       * first witness.
+       */
+      void reset_schedule( WitnessID first_witness )
+      {
+         _schedule.clear();
+         for( const WitnessID& wid : _ineligible_no_turn )
+         {
+            _eligible.push_back( wid );
+         }
+         _turns += _ineligible_no_turn.size();
+         _ineligible_no_turn.clear();
+         for( const auto& item : _ineligible_waiting_for_token )
+         {
+            _eligible.push_back( item.first );
+            _turns += (item.second ? 0 : 1);
+         }
+         _tokens += _ineligible_waiting_for_token.size();
+         _ineligible_waiting_for_token.clear();
+         if( debug ) check_invariant();
+
+         auto it = std::find( _eligible.begin(), _eligible.end(), first_witness );
+         assert( it != _eligible.end() );
+
+         _schedule.push_back( *it );
+         _ineligible_waiting_for_token.emplace_back( *it, false );
+         _eligible.erase( it );
+         _turns--;
+         _tokens--;
+         if( debug ) check_invariant();
+         return;
+      }
+
       // keep track of total turns / tokens in existence
       CountType _turns = 0;
       CountType _tokens = 0;