Distribute REX returns over time to REX owners

contracts/eosio.system/include/eosio.system/eosio.system.hpp

@@ -59,8 +59,10 @@ namespace eosiosystem {
 
    static constexpr uint32_t seconds_per_year      = 52 * 7 * 24 * 3600;
    static constexpr uint32_t seconds_per_day       = 24 * 3600;
+   static constexpr uint32_t seconds_per_hour      = 3600;
    static constexpr int64_t  useconds_per_year     = int64_t(seconds_per_year) * 1000'000ll;
    static constexpr int64_t  useconds_per_day      = int64_t(seconds_per_day) * 1000'000ll;
+   static constexpr int64_t  useconds_per_hour     = int64_t(seconds_per_hour) * 1000'000ll;
    static constexpr uint32_t blocks_per_day        = 2 * seconds_per_day; // half seconds per day
 
    static constexpr int64_t  min_activated_stake   = 150'000'000'0000;
@@ -333,6 +335,45 @@ namespace eosiosystem {
 
    typedef eosio::multi_index< "rexpool"_n, rex_pool > rex_pool_table;
 
+   // `rex_return_pool` structure underlying the rex return pool table. A rex return pool table entry is defined by:
+   // - `version` defaulted to zero,
+   // - `last_dist_time` the last time proceeds from renting, ram fees, and name bids were added to the rex pool,
+   // - `pending_bucket_time` timestamp of the pending 12-hour return bucket,
+   // - `oldest_bucket_time` cached timestamp of the oldest 12-hour return bucket, 
+   // - `pending_bucket_proceeds` proceeds in the pending 12-hour return bucket, 
+   // - `current_rate_of_increase` the current rate per dist_interval at which proceeds are added to the rex pool,
+   // - `proceeds` the maximum amount of proceeds that can be added to the rex pool at any given time
+   struct [[eosio::table,eosio::contract("eosio.system")]] rex_return_pool {
+      uint8_t        version = 0;
+      time_point_sec last_dist_time;
+      time_point_sec pending_bucket_time      = time_point_sec::maximum();
+      time_point_sec oldest_bucket_time       = time_point_sec::min();
+      int64_t        pending_bucket_proceeds  = 0;
+      int64_t        current_rate_of_increase = 0;
+      int64_t        proceeds                 = 0;
+
+      static constexpr uint32_t total_intervals  = 30 * 144; // 30 days
+      static constexpr uint32_t dist_interval    = 10 * 60;  // 10 minutes
+      static constexpr uint8_t  hours_per_bucket = 12;
+      static_assert( total_intervals * dist_interval == 30 * seconds_per_day );
+
+      uint64_t primary_key()const { return 0; }
+   };
+
+   typedef eosio::multi_index< "rexretpool"_n, rex_return_pool > rex_return_pool_table;
+
+   // `rex_return_buckets` structure underlying the rex return buckets table. A rex return buckets table is defined by:
+   // - `version` defaulted to zero,
+   // - `return_buckets` buckets of proceeds accumulated in 12-hour intervals 
+   struct [[eosio::table,eosio::contract("eosio.system")]] rex_return_buckets {
+      uint8_t                           version = 0;
+      std::map<time_point_sec, int64_t> return_buckets;
+
+      uint64_t primary_key()const { return 0; }
+   };
+
+   typedef eosio::multi_index< "retbuckets"_n, rex_return_buckets > rex_return_buckets_table;
+
    // `rex_fund` structure underlying the rex fund table. A rex fund table entry is defined by:
    // - `version` defaulted to zero,
    // - `owner` the owner of the rex fund,
@@ -430,22 +471,24 @@ namespace eosiosystem {
    class [[eosio::contract("eosio.system")]] system_contract : public native {
 
       private:
-         voters_table            _voters;
-         producers_table         _producers;
-         producers_table2        _producers2;
-         global_state_singleton  _global;
-         global_state2_singleton _global2;
-         global_state3_singleton _global3;
-         global_state4_singleton _global4;
-         eosio_global_state      _gstate;
-         eosio_global_state2     _gstate2;
-         eosio_global_state3     _gstate3;
-         eosio_global_state4     _gstate4;
-         rammarket               _rammarket;
-         rex_pool_table          _rexpool;
-         rex_fund_table          _rexfunds;
-         rex_balance_table       _rexbalance;
-         rex_order_table         _rexorders;
+         voters_table             _voters;
+         producers_table          _producers;
+         producers_table2         _producers2;
+         global_state_singleton   _global;
+         global_state2_singleton  _global2;
+         global_state3_singleton  _global3;
+         global_state4_singleton  _global4;
+         eosio_global_state       _gstate;
+         eosio_global_state2      _gstate2;
+         eosio_global_state3      _gstate3;
+         eosio_global_state4      _gstate4;
+         rammarket                _rammarket;
+         rex_pool_table           _rexpool;
+         rex_return_pool_table    _rexretpool;
+         rex_return_buckets_table _rexretbuckets;
+         rex_fund_table           _rexfunds;
+         rex_balance_table        _rexbalance;
+         rex_order_table          _rexorders;
 
       public:
          static constexpr eosio::name active_permission{"active"_n};
@@ -1121,6 +1164,7 @@ namespace eosiosystem {
 
          // defined in rex.cpp
          void runrex( uint16_t max );
+         void update_rex_pool();
          void update_resource_limits( const name& from, const name& receiver, int64_t delta_net, int64_t delta_cpu );
          void check_voting_requirement( const name& owner,
                                         const char* error_msg = "must vote for at least 21 producers or for a proxy before buying REX" )const;
@@ -1142,6 +1186,7 @@ namespace eosiosystem {
          static time_point_sec get_rex_maturity();
          asset add_to_rex_balance( const name& owner, const asset& payment, const asset& rex_received );
          asset add_to_rex_pool( const asset& payment );
+         void add_to_rex_return_pool( const asset& fee );
          void process_rex_maturities( const rex_balance_table::const_iterator& bitr );
          void consolidate_rex_balance( const rex_balance_table::const_iterator& bitr,
                                        const asset& rex_in_sell_order );

contracts/eosio.system/src/eosio.system.cpp

@@ -26,11 +26,12 @@ namespace eosiosystem {
     _global4(get_self(), get_self().value),
     _rammarket(get_self(), get_self().value),
     _rexpool(get_self(), get_self().value),
+    _rexretpool(get_self(), get_self().value),
+    _rexretbuckets(get_self(), get_self().value),
     _rexfunds(get_self(), get_self().value),
     _rexbalance(get_self(), get_self().value),
     _rexorders(get_self(), get_self().value)
    {
-      //print( "construct system\n" );
       _gstate  = _global.exists() ? _global.get() : get_default_parameters();
       _gstate2 = _global2.exists() ? _global2.get() : eosio_global_state2{};
       _gstate3 = _global3.exists() ? _global3.get() : eosio_global_state3{};

contracts/eosio.system/src/rex.cpp

@@ -6,6 +6,7 @@ namespace eosiosystem {
 
    using eosio::current_time_point;
    using eosio::token;
+   using eosio::seconds;
 
    void system_contract::deposit( const name& owner, const asset& amount )
    {
@@ -452,15 +453,13 @@ namespace eosiosystem {
     */
    void system_contract::add_loan_to_rex_pool( const asset& payment, int64_t rented_tokens, bool new_loan )
    {
+      add_to_rex_return_pool( payment );
       _rexpool.modify( _rexpool.begin(), same_payer, [&]( auto& rt ) {
          // add payment to total_rent
          rt.total_rent.amount    += payment.amount;
          // move rented_tokens from total_unlent to total_lent
          rt.total_unlent.amount  -= rented_tokens;
          rt.total_lent.amount    += rented_tokens;
-         // add payment to total_unlent
-         rt.total_unlent.amount  += payment.amount;
-         rt.total_lendable.amount = rt.total_unlent.amount + rt.total_lent.amount;
          // increment loan_num if a new loan is being created
          if ( new_loan ) {
             rt.loan_num++;
@@ -513,6 +512,8 @@ namespace eosiosystem {
    {
       check( rex_system_initialized(), "rex system not initialized yet" );
 
+      update_rex_pool();
+
       const auto& pool = _rexpool.begin();
 
       auto process_expired_loan = [&]( auto& idx, const auto& itr ) -> std::pair<bool, int64_t> {
@@ -616,6 +617,108 @@ namespace eosiosystem {
 
    }
 
+   /**
+    * @brief Adds returns from the REX return pool to the REX pool
+    */
+   void system_contract::update_rex_pool()
+   {
+      auto get_elapsed_intervals = [&]( const time_point_sec& t1, const time_point_sec& t0 ) -> uint32_t {
+         return ( t1.sec_since_epoch() - t0.sec_since_epoch() ) / rex_return_pool::dist_interval;
+      };
+
+      const time_point_sec ct             = current_time_point();
+      const uint32_t       cts            = ct.sec_since_epoch();
+      const time_point_sec effective_time{cts - cts % rex_return_pool::dist_interval};
+
+      const auto ret_pool_elem    = _rexretpool.begin();
+      const auto ret_buckets_elem = _rexretbuckets.begin();
+
+      if ( ret_pool_elem == _rexretpool.end() || effective_time <= ret_pool_elem->last_dist_time ) {
+         return;
+      }
+
+      const int64_t  current_rate      = ret_pool_elem->current_rate_of_increase;
+      const uint32_t elapsed_intervals = get_elapsed_intervals( effective_time, ret_pool_elem->last_dist_time );
+      int64_t        change_estimate   = current_rate * elapsed_intervals;
+
+      {
+         const bool new_return_bucket = ret_pool_elem->pending_bucket_time <= effective_time;
+         int64_t        new_bucket_rate = 0;
+         time_point_sec new_bucket_time = time_point_sec::min();
+         _rexretpool.modify( ret_pool_elem, same_payer, [&]( auto& rp ) {
+            if ( new_return_bucket ) {
+               int64_t remainder = rp.pending_bucket_proceeds % rex_return_pool::total_intervals;
+               new_bucket_rate   = ( rp.pending_bucket_proceeds - remainder ) / rex_return_pool::total_intervals;
+               new_bucket_time   = rp.pending_bucket_time;
+               rp.current_rate_of_increase += new_bucket_rate;
+               change_estimate             += remainder + new_bucket_rate * get_elapsed_intervals( effective_time, rp.pending_bucket_time );
+               rp.pending_bucket_proceeds   = 0;
+               rp.pending_bucket_time       = time_point_sec::maximum();
+               if ( new_bucket_time < rp.oldest_bucket_time ) {
+                  rp.oldest_bucket_time = new_bucket_time;
+               }
+            }
+            rp.proceeds      -= change_estimate;
+            rp.last_dist_time = effective_time;
+         });
+
+         if ( new_return_bucket ) {
+            _rexretbuckets.modify( ret_buckets_elem, same_payer, [&]( auto& rb ) {
+               rb.return_buckets[new_bucket_time] = new_bucket_rate;
+            });
+         }
+      }
+
+      const time_point_sec time_threshold = effective_time - seconds(rex_return_pool::total_intervals * rex_return_pool::dist_interval);
+      if ( ret_pool_elem->oldest_bucket_time <= time_threshold ) {
+         int64_t expired_rate = 0;
+         int64_t surplus      = 0;
+         _rexretbuckets.modify( ret_buckets_elem, same_payer, [&]( auto& rb ) {
+            auto& return_buckets = rb.return_buckets;
+            auto iter = return_buckets.begin();
+            while ( iter != return_buckets.end() && iter->first <= time_threshold ) {
+               auto next = iter;
+               ++next;
+               const uint32_t overtime = get_elapsed_intervals( effective_time,
+                                                                iter->first + seconds(rex_return_pool::total_intervals * rex_return_pool::dist_interval) );
+               surplus      += iter->second * overtime;
+               expired_rate += iter->second;
+               return_buckets.erase(iter);
+               iter = next;
+            }
+         });
+
+         _rexretpool.modify( ret_pool_elem, same_payer, [&]( auto& rp ) {
+            if ( !ret_buckets_elem->return_buckets.empty() ) {
+               rp.oldest_bucket_time = ret_buckets_elem->return_buckets.begin()->first;
+            } else {
+               rp.oldest_bucket_time = time_point_sec::min();
+            }
+            if ( expired_rate > 0) {
+               rp.current_rate_of_increase -= expired_rate;
+            }
+            if ( surplus > 0 ) {
+               change_estimate -= surplus;
+               rp.proceeds     += surplus;
+            }
+         });
+      }
+
+      if ( change_estimate > 0 && ret_pool_elem->proceeds < 0 ) {
+         _rexretpool.modify( ret_pool_elem, same_payer, [&]( auto& rp ) {
+            change_estimate += rp.proceeds;
+            rp.proceeds      = 0;
+         });
+      }
+
+      if ( change_estimate > 0 ) {
+         _rexpool.modify( _rexpool.begin(), same_payer, [&]( auto& pool ) {
+            pool.total_unlent.amount += change_estimate;
+            pool.total_lendable       = pool.total_unlent + pool.total_lent;
+         });
+      }
+   }
+
    template <typename T>
    int64_t system_contract::rent_rex( T& table, const name& from, const name& receiver, const asset& payment, const asset& fund )
    {
@@ -678,7 +781,7 @@ namespace eosiosystem {
       asset stake_change( 0, core_symbol() );
       bool  success = false;
 
-      const int64_t unlent_lower_bound = ( uint128_t(2) * rexitr->total_lent.amount ) / 10;
+      const int64_t unlent_lower_bound = rexitr->total_lent.amount / 10;
       const int64_t available_unlent   = rexitr->total_unlent.amount - unlent_lower_bound; // available_unlent <= 0 is possible
       if ( proceeds.amount <= available_unlent ) {
          const int64_t init_vote_stake_amount = bitr->vote_stake.amount;
@@ -818,10 +921,7 @@ namespace eosiosystem {
    {
 #if CHANNEL_RAM_AND_NAMEBID_FEES_TO_REX
       if ( rex_available() ) {
-         _rexpool.modify( _rexpool.begin(), same_payer, [&]( auto& rp ) {
-            rp.total_unlent.amount   += amount.amount;
-            rp.total_lendable.amount += amount.amount;
-         });
+         add_to_rex_return_pool( amount );
          // inline transfer to rex_account
          token::transfer_action transfer_act{ token_account, { from, active_permission } };
          transfer_act.send( from, rex_account, amount,
@@ -961,6 +1061,42 @@ namespace eosiosystem {
       return rex_received;
    }
 
+   /**
+    * @brief Adds an amount of core tokens to the REX return pool
+    *
+    * @param fee - amount to be added
+    */
+   void system_contract::add_to_rex_return_pool( const asset& fee )
+   {
+      update_rex_pool();
+      if ( fee.amount <= 0 ) {
+         return;
+      }
+
+      const time_point_sec ct              = current_time_point();
+      const uint32_t       cts             = ct.sec_since_epoch();
+      const uint32_t       bucket_interval = rex_return_pool::hours_per_bucket * seconds_per_hour;
+      const time_point_sec effective_time{cts - cts % bucket_interval + bucket_interval};
+      const auto return_pool_elem = _rexretpool.begin();
+      if ( return_pool_elem == _rexretpool.end() ) {
+         _rexretpool.emplace( get_self(), [&]( auto& rp ) {
+            rp.last_dist_time          = effective_time;
+            rp.pending_bucket_proceeds = fee.amount;
+            rp.pending_bucket_time     = effective_time;
+            rp.proceeds                = fee.amount;
+         });
+         _rexretbuckets.emplace( get_self(), [&]( auto& rb ) { } );
+      } else {
+         _rexretpool.modify( return_pool_elem, same_payer, [&]( auto& rp ) {
+            rp.pending_bucket_proceeds += fee.amount;
+            rp.proceeds                += fee.amount;
+            if ( rp.pending_bucket_time == time_point_sec::maximum() ) {
+               rp.pending_bucket_time = effective_time;
+            }
+         });
+      }
+   }
+
    /**
     * @brief Updates owner REX balance upon buying REX tokens
     *

tests/eosio.system_tester.hpp

@@ -638,6 +638,48 @@ class eosio_system_tester : public TESTER {
       return data.empty() ? fc::variant() : abi_ser.binary_to_variant( "rex_pool", data, abi_serializer_max_time );
    }
 
+   fc::variant get_rex_return_pool() const {
+      vector<char> data;
+      const auto& db = control->db();
+      namespace chain = eosio::chain;
+      const auto* t_id = db.find<eosio::chain::table_id_object, chain::by_code_scope_table>( boost::make_tuple( config::system_account_name, config::system_account_name, N(rexretpool) ) );
+      if ( !t_id ) {
+         return fc::variant();
+      }
+
+      const auto& idx = db.get_index<chain::key_value_index, chain::by_scope_primary>();
+
+      auto itr = idx.lower_bound( boost::make_tuple( t_id->id, 0 ) );
+      if ( itr == idx.end() || itr->t_id != t_id->id || 0 != itr->primary_key ) {
+         return fc::variant();
+      }
+
+      data.resize( itr->value.size() );
+      memcpy( data.data(), itr->value.data(), data.size() );
+      return data.empty() ? fc::variant() : abi_ser.binary_to_variant( "rex_return_pool", data, abi_serializer_max_time );
+   }
+
+   fc::variant get_rex_return_buckets() const {
+      vector<char> data;
+      const auto& db = control->db();
+      namespace chain = eosio::chain;
+      const auto* t_id = db.find<eosio::chain::table_id_object, chain::by_code_scope_table>( boost::make_tuple( config::system_account_name, config::system_account_name, N(retbuckets) ) );
+      if ( !t_id ) {
+         return fc::variant();
+      }
+
+      const auto& idx = db.get_index<chain::key_value_index, chain::by_scope_primary>();
+
+      auto itr = idx.lower_bound( boost::make_tuple( t_id->id, 0 ) );
+      if ( itr == idx.end() || itr->t_id != t_id->id || 0 != itr->primary_key ) {
+         return fc::variant();
+      }
+
+      data.resize( itr->value.size() );
+      memcpy( data.data(), itr->value.data(), data.size() );
+      return data.empty() ? fc::variant() : abi_ser.binary_to_variant( "rex_return_buckets", data, abi_serializer_max_time );
+   }
+
    void setup_rex_accounts( const std::vector<account_name>& accounts,
                             const asset& init_balance,
                             const asset& net = core_sym::from_string("80.0000"),