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// Copyright (c) 2016-2019 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_VERSIONBITS_H
#define BITCOIN_VERSIONBITS_H
#include <chain.h>
#include <sync.h>
#include <map>
/** What block version to use for new blocks (pre versionbits) */
static const int32_t VERSIONBITS_LAST_OLD_BLOCK_VERSION = 4;
/** What bits to set in version for versionbits blocks */
static const int32_t VERSIONBITS_TOP_BITS = 0x20000000UL;
/** What bitmask determines whether versionbits is in use */
static const int32_t VERSIONBITS_TOP_MASK = 0xE0000000UL;
/** Total bits available for versionbits */
static const int32_t VERSIONBITS_NUM_BITS = 29;
/** BIP 9 defines a finite-state-machine to deploy a softfork in multiple stages.
* State transitions happen during retarget period if conditions are met
* In case of reorg, transitions can go backward. Without transition, state is
* inherited between periods. All blocks of a period share the same state.
*/
enum class ThresholdState {
DEFINED, // First state that each softfork starts out as. The genesis block is by definition in this state for each deployment.
STARTED, // For blocks past the starttime.
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.
ACTIVE, // For all blocks after the LOCKED_IN retarget period (final state)
FAILED, // For all blocks once the first retarget period after the timeout time is hit, if LOCKED_IN wasn't already reached (final state)
};
// A map that gives the state for blocks whose height is a multiple of Period().
// The map is indexed by the block's parent, however, so all keys in the map
// will either be nullptr or a block with (height + 1) % Period() == 0.
typedef std::map<const CBlockIndex*, ThresholdState> ThresholdConditionCache;
/** Display status of an in-progress BIP9 softfork */
struct BIP9Stats {
/** Length of blocks of the BIP9 signalling period */
int period;
/** Number of blocks with the version bit set required to activate the softfork */
int threshold;
/** Number of blocks elapsed since the beginning of the current period */
int elapsed;
/** Number of blocks with the version bit set since the beginning of the current period */
int count;
/** False if there are not enough blocks left in this period to pass activation threshold */
bool possible;
};
/**
* Abstract class that implements BIP9-style threshold logic, and caches results.
*/
class AbstractThresholdConditionChecker {
protected:
virtual bool Condition(const CBlockIndex* pindex, const Consensus::Params& params) const =0;
virtual int64_t BeginTime(const Consensus::Params& params) const =0;
virtual int64_t EndTime(const Consensus::Params& params) const =0;
virtual int MinActivationHeight(const Consensus::Params& params) const { return 0; }
virtual int Period(const Consensus::Params& params) const =0;
virtual int Threshold(const Consensus::Params& params) const =0;
public:
/** Returns the numerical statistics of an in-progress BIP9 softfork in the current period */
BIP9Stats GetStateStatisticsFor(const CBlockIndex* pindex, const Consensus::Params& params) const;
/** Returns the state for pindex A based on parent pindexPrev B. Applies any state transition if conditions are present.
* Caches state from first block of period. */
ThresholdState GetStateFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const;
/** 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 */
int GetStateSinceHeightFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const;
};
/** BIP 9 allows multiple softforks to be deployed in parallel. We cache
* per-period state for every one of them. */
class VersionBitsCache
{
private:
Mutex m_mutex;
ThresholdConditionCache m_caches[Consensus::MAX_VERSION_BITS_DEPLOYMENTS] GUARDED_BY(m_mutex);
public:
/** Get the numerical statistics for a given deployment for the signalling period that includes the block after pindexPrev. */
static BIP9Stats Statistics(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos);
static uint32_t Mask(const Consensus::Params& params, Consensus::DeploymentPos pos);
/** Get the BIP9 state for a given deployment for the block after pindexPrev. */
ThresholdState State(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos);
/** Get the block height at which the BIP9 deployment switched into the state for the block after pindexPrev. */
int StateSinceHeight(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos);
/** Determine what nVersion a new block should use
*/
int32_t ComputeBlockVersion(const CBlockIndex* pindexPrev, const Consensus::Params& params);
void Clear();
};
#endif // BITCOIN_VERSIONBITS_H
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