1  // Copyright (c) 2016-2022 The Bitcoin Core developers
  2  // Distributed under the MIT software license, see the accompanying
  3  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  4  
  5  #ifndef BITCOIN_VERSIONBITS_H
  6  #define BITCOIN_VERSIONBITS_H
  7  
  8  #include <chain.h>
  9  #include <sync.h>
 10  
 11  #include <map>
 12  
 13  /** What block version to use for new blocks (pre versionbits) */
 14  static const int32_t VERSIONBITS_LAST_OLD_BLOCK_VERSION = 4;
 15  /** What bits to set in version for versionbits blocks */
 16  static const int32_t VERSIONBITS_TOP_BITS = 0x20000000UL;
 17  /** What bitmask determines whether versionbits is in use */
 18  static const int32_t VERSIONBITS_TOP_MASK = 0xE0000000UL;
 19  /** Total bits available for versionbits */
 20  static const int32_t VERSIONBITS_NUM_BITS = 29;
 21  
 22  /** BIP 9 defines a finite-state-machine to deploy a softfork in multiple stages.
 23   *  State transitions happen during retarget period if conditions are met
 24   *  In case of reorg, transitions can go backward. Without transition, state is
 25   *  inherited between periods. All blocks of a period share the same state.
 26   */
 27  enum class ThresholdState {
 28      DEFINED,   // First state that each softfork starts out as. The genesis block is by definition in this state for each deployment.
 29      STARTED,   // For blocks past the starttime.
 30      LOCKED_IN, // For at least one retarget period after the first retarget period with STARTED blocks of which at least threshold have the associated bit set in nVersion, until min_activation_height is reached.
 31      ACTIVE,    // For all blocks after the LOCKED_IN retarget period (final state)
 32      FAILED,    // For all blocks once the first retarget period after the timeout time is hit, if LOCKED_IN wasn't already reached (final state)
 33  };
 34  
 35  // A map that gives the state for blocks whose height is a multiple of Period().
 36  // The map is indexed by the block's parent, however, so all keys in the map
 37  // will either be nullptr or a block with (height + 1) % Period() == 0.
 38  typedef std::map<const CBlockIndex*, ThresholdState> ThresholdConditionCache;
 39  
 40  /** Display status of an in-progress BIP9 softfork */
 41  struct BIP9Stats {
 42      /** Length of blocks of the BIP9 signalling period */
 43      int period;
 44      /** Number of blocks with the version bit set required to activate the softfork */
 45      int threshold;
 46      /** Number of blocks elapsed since the beginning of the current period */
 47      int elapsed;
 48      /** Number of blocks with the version bit set since the beginning of the current period */
 49      int count;
 50      /** False if there are not enough blocks left in this period to pass activation threshold */
 51      bool possible;
 52  };
 53  
 54  /**
 55   * Abstract class that implements BIP9-style threshold logic, and caches results.
 56   */
 57  class AbstractThresholdConditionChecker {
 58  protected:
 59      virtual bool Condition(const CBlockIndex* pindex, const Consensus::Params& params) const =0;
 60      virtual int64_t BeginTime(const Consensus::Params& params) const =0;
 61      virtual int64_t EndTime(const Consensus::Params& params) const =0;
 62      virtual int MinActivationHeight(const Consensus::Params& params) const { return 0; }
 63      virtual int Period(const Consensus::Params& params) const =0;
 64      virtual int Threshold(const Consensus::Params& params) const =0;
 65  
 66  public:
 67      /** Returns the numerical statistics of an in-progress BIP9 softfork in the period including pindex
 68       * If provided, signalling_blocks is set to true/false based on whether each block in the period signalled
 69       */
 70      BIP9Stats GetStateStatisticsFor(const CBlockIndex* pindex, const Consensus::Params& params, std::vector<bool>* signalling_blocks = nullptr) const;
 71      /** Returns the state for pindex A based on parent pindexPrev B. Applies any state transition if conditions are present.
 72       *  Caches state from first block of period. */
 73      ThresholdState GetStateFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const;
 74      /** Returns the height since when the ThresholdState has started for pindex A based on parent pindexPrev B, all blocks of a period share the same */
 75      int GetStateSinceHeightFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const;
 76  };
 77  
 78  /** BIP 9 allows multiple softforks to be deployed in parallel. We cache
 79   *  per-period state for every one of them. */
 80  class VersionBitsCache
 81  {
 82  private:
 83      Mutex m_mutex;
 84      ThresholdConditionCache m_caches[Consensus::MAX_VERSION_BITS_DEPLOYMENTS] GUARDED_BY(m_mutex);
 85  
 86  public:
 87      /** Get the numerical statistics for a given deployment for the signalling period that includes pindex.
 88       * If provided, signalling_blocks is set to true/false based on whether each block in the period signalled
 89       */
 90      static BIP9Stats Statistics(const CBlockIndex* pindex, const Consensus::Params& params, Consensus::DeploymentPos pos, std::vector<bool>* signalling_blocks = nullptr);
 91  
 92      static uint32_t Mask(const Consensus::Params& params, Consensus::DeploymentPos pos);
 93  
 94      /** Get the BIP9 state for a given deployment for the block after pindexPrev. */
 95      ThresholdState State(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
 96  
 97      /** Get the block height at which the BIP9 deployment switched into the state for the block after pindexPrev. */
 98      int StateSinceHeight(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
 99  
100      /** Determine what nVersion a new block should use
101       */
102      int32_t ComputeBlockVersion(const CBlockIndex* pindexPrev, const Consensus::Params& params) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
103  
104      void Clear() EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
105  };
106  
107  #endif // BITCOIN_VERSIONBITS_H