The version-bits threshold state machine interface

1// Copyright (c) 2016-present 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_IMPL_H
6#define BITCOIN_VERSIONBITS_IMPL_H
7
8#include <chain.h>
9#include <sync.h>
10#include <versionbits.h>
11
12/** BIP 9 defines a finite-state-machine to deploy a softfork in multiple stages.
13 *  State transitions happen during retarget period if conditions are met
14 *  In case of reorg, transitions can go backward. Without transition, state is
15 *  inherited between periods. All blocks of a period share the same state.
16 */
17enum class ThresholdState : uint8_t {
18    DEFINED,   // First state that each softfork starts out as. The genesis block is by definition in this state for each deployment.
19    STARTED,   // For blocks past the starttime.
20    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.
21    ACTIVE,    // For all blocks after the LOCKED_IN retarget period (final state)
22    FAILED,    // For all blocks once the first retarget period after the timeout time is hit, if LOCKED_IN wasn't already reached (final state)
23};
24
25/** Get a string with the state name */
26std::string StateName(ThresholdState state);
27
28/**
29 * Abstract class that implements BIP9-style threshold logic, and caches results.
30 */
31class AbstractThresholdConditionChecker {
32protected:
33    virtual bool Condition(const CBlockIndex* pindex) const =0;
34    virtual int64_t BeginTime() const =0;
35    virtual int64_t EndTime() const =0;
36    virtual int MinActivationHeight() const { return 0; }
37    virtual int Period() const =0;
38    virtual int Threshold() const =0;
39
40public:
41    virtual ~AbstractThresholdConditionChecker() = default;
42
43    /** Returns the numerical statistics of an in-progress BIP9 softfork in the period including pindex
44     * If provided, signalling_blocks is set to true/false based on whether each block in the period signalled
45     */
46    BIP9Stats GetStateStatisticsFor(const CBlockIndex* pindex, std::vector<bool>* signalling_blocks = nullptr) const;
47    /** Returns the state for pindex A based on parent pindexPrev B. Applies any state transition if conditions are present.
48     *  Caches state from first block of period. */
49    ThresholdState GetStateFor(const CBlockIndex* pindexPrev, ThresholdConditionCache& cache) const;
50    /** 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 */
51    int GetStateSinceHeightFor(const CBlockIndex* pindexPrev, ThresholdConditionCache& cache) const;
52};
53
54/**
55 * Class to implement versionbits logic.
56 */
57class VersionBitsConditionChecker : public AbstractThresholdConditionChecker {
58private:
59    const Consensus::BIP9Deployment& dep;
60
61protected:
62    int64_t BeginTime() const override { return dep.nStartTime; }
63    int64_t EndTime() const override { return dep.nTimeout; }
64    int MinActivationHeight() const override { return dep.min_activation_height; }
65    int Period() const override { return dep.period; }
66    int Threshold() const override { return dep.threshold; }
67
68    bool Condition(const CBlockIndex* pindex) const override
69    {
70        return Condition(pindex->nVersion);
71    }
72
73public:
74    explicit VersionBitsConditionChecker(const Consensus::BIP9Deployment& dep) : dep{dep} {}
75    explicit VersionBitsConditionChecker(const Consensus::Params& params, Consensus::DeploymentPos id) : VersionBitsConditionChecker{params.vDeployments[id]} {}
76
77    uint32_t Mask() const { return (uint32_t{1}) << dep.bit; }
78
79    bool Condition(int32_t nVersion) const
80    {
81        return (((nVersion & VERSIONBITS_TOP_MASK) == VERSIONBITS_TOP_BITS) && (nVersion & Mask()) != 0);
82    }
83};
84
85#endif // BITCOIN_VERSIONBITS_IMPL_H
86