utils: add RoundEvent (#482)

* Move core.roundBasedConfig to core/utils
* Refine utils.RoundBasedConfig
* Add utils.RoundEvent

8 files changed, 496 insertions, 76 deletions

diff --git a/core/agreement-mgr.go b/core/agreement-mgr.go
index 88cc432..7b5effb 100644
--- a/core/agreement-mgr.go
+++ b/core/agreement-mgr.go
@@ -65,7 +65,7 @@ func genValidLeader(
 }
 
 type agreementMgrConfig struct {
-	roundBasedConfig
+	utils.RoundBasedConfig
 
 	notarySetSize uint32
 	lambdaBA      time.Duration
@@ -77,14 +77,14 @@ func (c *agreementMgrConfig) from(
 	c.notarySetSize = config.NotarySetSize
 	c.lambdaBA = config.LambdaBA
 	c.crs = crs
-	c.setupRoundBasedFields(round, config)
+	c.SetupRoundBasedFields(round, config)
 }
 
 func newAgreementMgrConfig(prev agreementMgrConfig, config *types.Config,
 	crs common.Hash) (c agreementMgrConfig) {
 	c = agreementMgrConfig{}
-	c.from(prev.roundID+1, config, crs)
-	c.setRoundBeginHeight(prev.roundEndHeight)
+	c.from(prev.RoundID()+1, config, crs)
+	c.AppendTo(prev.RoundBasedConfig)
 	return
 }
 
@@ -356,7 +356,7 @@ Loop:
 		setting.recv.isNotary = checkRound()
 		// Run BA for this round.
 		setting.recv.roundValue.Store(currentRound)
-		setting.recv.changeNotaryHeight = curConfig.roundEndHeight
+		setting.recv.changeNotaryHeight = curConfig.RoundEndHeight()
 		setting.recv.restartNotary <- types.Position{
 			Round:  setting.recv.round(),
 			Height: math.MaxUint64,
diff --git a/core/blockchain.go b/core/blockchain.go
index b6c8b1d..19a580b 100644
--- a/core/blockchain.go
+++ b/core/blockchain.go
@@ -103,21 +103,21 @@ func (pb pendingBlockRecords) searchByPosition(p types.Position) (
 }
 
 type blockChainConfig struct {
-	roundBasedConfig
+	utils.RoundBasedConfig
 
 	minBlockInterval time.Duration
 }
 
 func (c *blockChainConfig) fromConfig(round uint64, config *types.Config) {
 	c.minBlockInterval = config.MinBlockInterval
-	c.setupRoundBasedFields(round, config)
+	c.SetupRoundBasedFields(round, config)
 }
 
 func newBlockChainConfig(prev blockChainConfig, config *types.Config) (
 	c blockChainConfig) {
 	c = blockChainConfig{}
-	c.fromConfig(prev.roundID+1, config)
-	c.setRoundBeginHeight(prev.roundEndHeight)
+	c.fromConfig(prev.RoundID()+1, config)
+	c.AppendTo(prev.RoundBasedConfig)
 	return
 }
 
@@ -145,14 +145,14 @@ func newBlockChain(nID types.NodeID, dMoment time.Time, initBlock *types.Block,
 	initConfig blockChainConfig, app Application, vGetter tsigVerifierGetter,
 	signer *utils.Signer, logger common.Logger) *blockChain {
 	if initBlock != nil {
-		if initConfig.roundID != initBlock.Position.Round {
+		if initConfig.RoundID() != initBlock.Position.Round {
 			panic(fmt.Errorf("incompatible config/block %s %d",
-				initBlock, initConfig.roundID))
+				initBlock, initConfig.RoundID()))
 		}
 	} else {
-		if initConfig.roundID != 0 {
+		if initConfig.RoundID() != 0 {
 			panic(fmt.Errorf("genesis config should from round 0 %d",
-				initConfig.roundID))
+				initConfig.RoundID()))
 		}
 	}
 	return &blockChain{
@@ -235,7 +235,7 @@ func (bc *blockChain) sanityCheck(b *types.Block) error {
 		return ErrInvalidBlockHeight
 	}
 	tipConfig := bc.tipConfig()
-	if tipConfig.isLastBlock(bc.lastConfirmed) {
+	if tipConfig.IsLastBlock(bc.lastConfirmed) {
 		if b.Position.Round != bc.lastConfirmed.Position.Round+1 {
 			return ErrRoundNotSwitch
 		}
@@ -359,7 +359,7 @@ func (bc *blockChain) tipRound() uint64 {
 		return 0
 	}
 	offset, tipConfig := uint64(0), bc.tipConfig()
-	if tipConfig.isLastBlock(bc.lastConfirmed) {
+	if tipConfig.IsLastBlock(bc.lastConfirmed) {
 		offset++
 	}
 	return bc.lastConfirmed.Position.Round + offset
@@ -499,12 +499,12 @@ func (bc *blockChain) checkIfBlocksConfirmed() {
 }
 
 func (bc *blockChain) purgeConfig() {
-	for bc.configs[0].roundID < bc.lastConfirmed.Position.Round {
+	for bc.configs[0].RoundID() < bc.lastConfirmed.Position.Round {
 		bc.configs = bc.configs[1:]
 	}
-	if bc.configs[0].roundID != bc.lastConfirmed.Position.Round {
+	if bc.configs[0].RoundID() != bc.lastConfirmed.Position.Round {
 		panic(fmt.Errorf("mismatched tip config: %d %d",
-			bc.configs[0].roundID, bc.lastConfirmed.Position.Round))
+			bc.configs[0].RoundID(), bc.lastConfirmed.Position.Round))
 	}
 }
 
@@ -556,7 +556,7 @@ func (bc *blockChain) prepareBlock(position types.Position,
 			b, err = nil, ErrNotFollowTipPosition
 			return
 		}
-		if tipConfig.isLastBlock(tip) {
+		if tipConfig.IsLastBlock(tip) {
 			if tip.Position.Round+1 != position.Round {
 				b, err = nil, ErrRoundNotSwitch
 				return
@@ -610,9 +610,9 @@ func (bc *blockChain) tipConfig() blockChainConfig {
 	if bc.lastConfirmed == nil {
 		panic(fmt.Errorf("attempting to access config without tip"))
 	}
-	if bc.lastConfirmed.Position.Round != bc.configs[0].roundID {
+	if bc.lastConfirmed.Position.Round != bc.configs[0].RoundID() {
 		panic(fmt.Errorf("inconsist config and tip: %d %d",
-			bc.lastConfirmed.Position.Round, bc.configs[0].roundID))
+			bc.lastConfirmed.Position.Round, bc.configs[0].RoundID()))
 	}
 	return bc.configs[0]
 }
diff --git a/core/blockchain_test.go b/core/blockchain_test.go
index 46e7630..c5023ff 100644
--- a/core/blockchain_test.go
+++ b/core/blockchain_test.go
@@ -139,9 +139,9 @@ func (s *BlockChainTestSuite) newBlockChain(initB *types.Block,
 		RoundLength:      roundLength,
 	})
 	if initB != nil {
-		initConfig.setRoundBeginHeight(initB.Position.Height)
+		initConfig.SetRoundBeginHeight(initB.Position.Height)
 	} else {
-		initConfig.setRoundBeginHeight(0)
+		initConfig.SetRoundBeginHeight(0)
 	}
 	return newBlockChain(s.nID, s.dMoment, initB, initConfig,
 		test.NewApp(0, nil), &testTSigVerifierGetter{}, s.signer,
diff --git a/core/consensus.go b/core/consensus.go
index d2c6dc3..e3a7b1a 100644
--- a/core/consensus.go
+++ b/core/consensus.go
@@ -545,7 +545,7 @@ func newConsensusForRound(
 	}
 	bcConfig := blockChainConfig{}
 	bcConfig.fromConfig(initRound, initConfig)
-	bcConfig.setRoundBeginHeight(initRoundBeginHeight)
+	bcConfig.SetRoundBeginHeight(initRoundBeginHeight)
 	bcModule := newBlockChain(ID, dMoment, initBlock, bcConfig, appModule,
 		NewTSigVerifierCache(gov, 7), signer, logger)
 	// Construct Consensus instance.
@@ -573,7 +573,7 @@ func newConsensusForRound(
 	con.ctx, con.ctxCancel = context.WithCancel(context.Background())
 	baConfig := agreementMgrConfig{}
 	baConfig.from(initRound, initConfig, initCRS)
-	baConfig.setRoundBeginHeight(initRoundBeginHeight)
+	baConfig.SetRoundBeginHeight(initRoundBeginHeight)
 	var err error
 	con.baMgr, err = newAgreementMgr(con, initRound, baConfig)
 	if err != nil {
diff --git a/core/round-based-config.go b/core/round-based-config.go
deleted file mode 100644
index 4f3a4cb..0000000
--- a/core/round-based-config.go
+++ /dev/null
@@ -1,51 +0,0 @@
-// Copyright 2018 The dexon-consensus Authors
-// This file is part of the dexon-consensus library.
-//
-// The dexon-consensus library is free software: you can redistribute it
-// and/or modify it under the terms of the GNU Lesser General Public License as
-// published by the Free Software Foundation, either version 3 of the License,
-// or (at your option) any later version.
-//
-// The dexon-consensus library is distributed in the hope that it will be
-// useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
-// General Public License for more details.
-//
-// You should have received a copy of the GNU Lesser General Public License
-// along with the dexon-consensus library. If not, see
-// <http://www.gnu.org/licenses/>.
-
-package core
-
-import (
-	"fmt"
-
-	"github.com/dexon-foundation/dexon-consensus/core/types"
-)
-
-type roundBasedConfig struct {
-	roundID          uint64
-	roundBeginHeight uint64
-	roundEndHeight   uint64
-	roundInterval    uint64
-}
-
-func (config *roundBasedConfig) setupRoundBasedFields(
-	roundID uint64, cfg *types.Config) {
-	config.roundID = roundID
-	config.roundInterval = cfg.RoundLength
-}
-
-func (config *roundBasedConfig) setRoundBeginHeight(begin uint64) {
-	config.roundBeginHeight = begin
-	config.roundEndHeight = begin + config.roundInterval
-}
-
-// isLastBlock checks if a block is the last block of this round.
-func (config *roundBasedConfig) isLastBlock(b *types.Block) bool {
-	if b.Position.Round != config.roundID {
-		panic(fmt.Errorf("attempt to compare by different round: %s, %d",
-			b, config.roundID))
-	}
-	return b.Position.Height+1 == config.roundEndHeight
-}
diff --git a/core/utils/round-based-config.go b/core/utils/round-based-config.go
new file mode 100644
index 0000000..3219a13
--- /dev/null
+++ b/core/utils/round-based-config.go
@@ -0,0 +1,112 @@
+// Copyright 2018 The dexon-consensus Authors
+// This file is part of the dexon-consensus library.
+//
+// The dexon-consensus library is free software: you can redistribute it
+// and/or modify it under the terms of the GNU Lesser General Public License as
+// published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The dexon-consensus library is distributed in the hope that it will be
+// useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the dexon-consensus library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package utils
+
+import (
+	"fmt"
+
+	"github.com/dexon-foundation/dexon-consensus/core/types"
+)
+
+// RoundBasedConfig is based config for rounds and provide boundary checking
+// for rounds.
+type RoundBasedConfig struct {
+	roundID          uint64
+	roundBeginHeight uint64
+	roundEndHeight   uint64
+	roundLength      uint64
+}
+
+// SetupRoundBasedFields setup round based fields, including round ID, the
+// length of rounds.
+func (c *RoundBasedConfig) SetupRoundBasedFields(
+	roundID uint64, cfg *types.Config) {
+	if c.roundLength > 0 {
+		panic(fmt.Errorf("duplicated set round based fields: %d",
+			c.roundLength))
+	}
+	c.roundID = roundID
+	c.roundLength = cfg.RoundLength
+}
+
+// SetRoundBeginHeight gives the beginning height for the initial round provided
+// when constructed.
+func (c *RoundBasedConfig) SetRoundBeginHeight(begin uint64) {
+	if c.roundBeginHeight != 0 {
+		panic(fmt.Errorf("duplicated set round begin height: %d",
+			c.roundBeginHeight))
+	}
+	c.roundBeginHeight = begin
+	c.roundEndHeight = begin + c.roundLength
+}
+
+// IsLastBlock checks if a block is the last block of this round.
+func (c *RoundBasedConfig) IsLastBlock(b *types.Block) bool {
+	if b.Position.Round != c.roundID {
+		panic(fmt.Errorf("attempt to compare by different round: %s, %d",
+			b, c.roundID))
+	}
+	return b.Position.Height+1 == c.roundEndHeight
+}
+
+// ExtendLength extends round ending height by the length of current round.
+func (c *RoundBasedConfig) ExtendLength() {
+	c.roundEndHeight += c.roundLength
+}
+
+// Contains checks if a block height is in this round.
+func (c *RoundBasedConfig) Contains(h uint64) bool {
+	return c.roundBeginHeight <= h && c.roundEndHeight > h
+}
+
+// RoundID returns the round ID of this config.
+func (c *RoundBasedConfig) RoundID() uint64 {
+	if c.roundLength == 0 {
+		panic(fmt.Errorf("config is not initialized: %d", c.roundID))
+	}
+	return c.roundID
+}
+
+// RoundEndHeight returns next checkpoint to varify if this round is ended.
+func (c *RoundBasedConfig) RoundEndHeight() uint64 {
+	if c.roundLength == 0 {
+		panic(fmt.Errorf("config is not initialized: %d", c.roundID))
+	}
+	return c.roundEndHeight
+}
+
+// AppendTo a config in previous round.
+func (c *RoundBasedConfig) AppendTo(other RoundBasedConfig) {
+	if c.roundID != other.roundID+1 {
+		panic(fmt.Errorf("round IDs of configs not continuous: %d %d",
+			c.roundID, other.roundID))
+	}
+	c.SetRoundBeginHeight(other.roundEndHeight)
+}
+
+// LastPeriodBeginHeight returns the begin height of last period. For example,
+// if a round is extended twice, then the return from this method is:
+//
+//    begin + 2 * roundLength - roundLength
+//
+func (c *RoundBasedConfig) LastPeriodBeginHeight() uint64 {
+	if c.roundLength == 0 {
+		panic(fmt.Errorf("config is not initialized: %d", c.roundID))
+	}
+	return c.roundEndHeight - c.roundLength
+}
diff --git a/core/utils/round-based-config_test.go b/core/utils/round-based-config_test.go
new file mode 100644
index 0000000..084efe2
--- /dev/null
+++ b/core/utils/round-based-config_test.go
@@ -0,0 +1,57 @@
+// Copyright 2019 The dexon-consensus Authors
+// This file is part of the dexon-consensus library.
+//
+// The dexon-consensus library is free software: you can redistribute it
+// and/or modify it under the terms of the GNU Lesser General Public License as
+// published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The dexon-consensus library is distributed in the hope that it will be
+// useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the dexon-consensus library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package utils
+
+import (
+	"testing"
+
+	"github.com/dexon-foundation/dexon-consensus/core/types"
+	"github.com/stretchr/testify/suite"
+)
+
+type RoundBasedConfigTestSuite struct {
+	suite.Suite
+}
+
+func (s *RoundBasedConfigTestSuite) TestBasicUsage() {
+	c1 := RoundBasedConfig{}
+	c1.SetupRoundBasedFields(1, &types.Config{RoundLength: 100})
+	c1.SetRoundBeginHeight(11)
+	s.Require().Equal(c1.RoundID(), uint64(1))
+	s.Require().Equal(c1.roundLength, uint64(100))
+	s.Require().Equal(c1.roundBeginHeight, uint64(11))
+	s.Require().Equal(c1.roundEndHeight, uint64(111))
+	s.Require().True(c1.Contains(110))
+	s.Require().False(c1.Contains(111))
+	c1.ExtendLength()
+	s.Require().True(c1.Contains(111))
+	s.Require().True(c1.Contains(210))
+	s.Require().False(c1.Contains(211))
+	s.Require().Equal(c1.LastPeriodBeginHeight(), uint64(111))
+	s.Require().Equal(c1.RoundEndHeight(), uint64(211))
+	// Test AppendTo.
+	c2 := RoundBasedConfig{}
+	c2.SetupRoundBasedFields(2, &types.Config{RoundLength: 50})
+	c2.AppendTo(c1)
+	s.Require().Equal(c2.roundBeginHeight, uint64(211))
+	s.Require().Equal(c2.roundEndHeight, uint64(261))
+}
+
+func TestRoundBasedConfig(t *testing.T) {
+	suite.Run(t, new(RoundBasedConfigTestSuite))
+}
diff --git a/core/utils/round-event.go b/core/utils/round-event.go
new file mode 100644
index 0000000..bab1d32
--- /dev/null
+++ b/core/utils/round-event.go
@@ -0,0 +1,302 @@
+// Copyright 2019 The dexon-consensus Authors
+// This file is part of the dexon-consensus library.
+//
+// The dexon-consensus library is free software: you can redistribute it
+// and/or modify it under the terms of the GNU Lesser General Public License as
+// published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The dexon-consensus library is distributed in the hope that it will be
+// useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+// General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the dexon-consensus library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package utils
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"time"
+
+	"github.com/dexon-foundation/dexon-consensus/common"
+	"github.com/dexon-foundation/dexon-consensus/core/types"
+	typesDKG "github.com/dexon-foundation/dexon-consensus/core/types/dkg"
+)
+
+// ErrUnmatchedBlockHeightWithGov is for invalid parameters for NewRoundEvent.
+type ErrUnmatchedBlockHeightWithGov struct {
+	round       uint64
+	reset       uint64
+	blockHeight uint64
+}
+
+func (e ErrUnmatchedBlockHeightWithGov) Error() string {
+	return fmt.Sprintf("unsynced block height and gov: round:%d reset:%d h:%d",
+		e.round, e.reset, e.blockHeight)
+}
+
+// RoundEventParam defines the parameters passed to event handlers of
+// RoundEvent.
+type RoundEventParam struct {
+	// 'Round' of next checkpoint, might be identical to previous checkpoint.
+	Round uint64
+	// the count of reset DKG for 'Round+1'.
+	Reset uint64
+	// the begin block height of this event, the end block height of this event
+	// would be BeginHeight + config.RoundLength.
+	BeginHeight uint64
+	// The configuration for 'Round'.
+	Config *types.Config
+	// The CRS for 'Round'.
+	CRS common.Hash
+}
+
+// NextRoundCheckpoint returns the height to check if the next round is ready.
+func (e RoundEventParam) NextRoundCheckpoint() uint64 {
+	return e.BeginHeight + e.Config.RoundLength*8/10
+}
+
+// roundEventFn defines the fingerprint of handlers of round events.
+type roundEventFn func([]RoundEventParam)
+
+// governanceAccessor is a subset of core.Governance to break the dependency
+// between core and utils package.
+type governanceAccessor interface {
+	// Configuration returns the configuration at a given round.
+	// Return the genesis configuration if round == 0.
+	Configuration(round uint64) *types.Config
+
+	// CRS returns the CRS for a given round.
+	// Return the genesis CRS if round == 0.
+	CRS(round uint64) common.Hash
+
+	// DKGComplaints gets all the DKGComplaints of round.
+	DKGComplaints(round uint64) []*typesDKG.Complaint
+
+	// DKGMasterPublicKeys gets all the DKGMasterPublicKey of round.
+	DKGMasterPublicKeys(round uint64) []*typesDKG.MasterPublicKey
+
+	// IsDKGFinal checks if DKG is final.
+	IsDKGFinal(round uint64) bool
+
+	// DKGResetCount returns the reset count for DKG of given round.
+	DKGResetCount(round uint64) uint64
+}
+
+// RoundEvent would be triggered when either:
+// - the next DKG set setup is ready.
+// - the next DKG set setup is failed, and previous DKG set already reset the
+//   CRS.
+type RoundEvent struct {
+	gov                     governanceAccessor
+	logger                  common.Logger
+	lock                    sync.Mutex
+	handlers                []roundEventFn
+	config                  RoundBasedConfig
+	lastTriggeredRound      uint64
+	lastTriggeredResetCount uint64
+	roundShift              uint64
+	ctx                     context.Context
+	ctxCancel               context.CancelFunc
+}
+
+// NewRoundEvent creates an RoundEvent instance.
+func NewRoundEvent(parentCtx context.Context, gov governanceAccessor,
+	logger common.Logger, initRound uint64,
+	initRoundBeginHeight, initBlockHeight uint64,
+	roundShift uint64) (*RoundEvent, error) {
+	// We need to generate valid ending block height of this round (taken
+	// DKG reset count into consideration).
+	e := &RoundEvent{
+		gov:                gov,
+		logger:             logger,
+		lastTriggeredRound: initRound,
+		roundShift:         roundShift,
+	}
+	e.ctx, e.ctxCancel = context.WithCancel(parentCtx)
+	e.config = RoundBasedConfig{}
+	e.config.SetupRoundBasedFields(initRound, GetConfigWithPanic(
+		gov, initRound, logger))
+	e.config.SetRoundBeginHeight(initRoundBeginHeight)
+	// Make sure the DKG reset count in current governance can cover the initial
+	// block height.
+	resetCount := gov.DKGResetCount(initRound + 1)
+	remains := resetCount
+	for ; resetCount > 0 && !e.config.Contains(initBlockHeight); remains-- {
+		e.config.ExtendLength()
+	}
+	if !e.config.Contains(initBlockHeight) {
+		return nil, ErrUnmatchedBlockHeightWithGov{
+			round:       initRound,
+			reset:       resetCount,
+			blockHeight: initBlockHeight,
+		}
+	}
+	e.lastTriggeredResetCount = resetCount - remains
+	return e, nil
+}
+
+// Register a handler to be called when new round is confirmed or new DKG reset
+// is detected.
+func (e *RoundEvent) Register(h roundEventFn) {
+	e.lock.Lock()
+	defer e.lock.Unlock()
+	e.handlers = append(e.handlers, h)
+}
+
+// ValidateNextRound validate if the DKG set for next round is ready to go or
+// failed to setup, all registered handlers would be called once some decision
+// is made on chain.
+//
+// This method would block until at least one event is triggered. Multiple
+// trigger in one call is possible.
+func (e *RoundEvent) ValidateNextRound(blockHeight uint64) {
+	// To make triggers continuous and sequential, the next validation should
+	// wait for previous one finishing. That's why I use mutex here directly.
+	var events []RoundEventParam
+	e.lock.Lock()
+	defer e.lock.Unlock()
+	e.logger.Info("ValidateNextRound",
+		"height", blockHeight,
+		"round", e.lastTriggeredRound,
+		"count", e.lastTriggeredResetCount)
+	defer func() {
+		if len(events) == 0 {
+			return
+		}
+		for _, h := range e.handlers {
+			// To make sure all handlers receive triggers sequentially, we can't
+			// raise go routines here.
+			h(events)
+		}
+	}()
+	startRound := e.lastTriggeredRound
+	for {
+		var (
+			dkgFailed, triggered bool
+			param                RoundEventParam
+			beginHeight          = blockHeight
+		)
+		for {
+			param, dkgFailed, triggered = e.check(beginHeight, startRound,
+				dkgFailed)
+			if !triggered {
+				break
+			}
+			events = append(events, param)
+			beginHeight = param.BeginHeight
+		}
+		if len(events) > 0 {
+			break
+		}
+		select {
+		case <-e.ctx.Done():
+			return
+		case <-time.After(500 * time.Millisecond):
+		}
+	}
+}
+
+func (e *RoundEvent) check(blockHeight, startRound uint64, lastDKGCheck bool) (
+	param RoundEventParam, dkgFailed bool, triggered bool) {
+	defer func() {
+		if !triggered {
+			return
+		}
+		// A simple assertion to make sure we didn't pick the wrong round.
+		if e.config.RoundID() != e.lastTriggeredRound {
+			panic(fmt.Errorf("triggered round not matched: %d, %d",
+				e.config.RoundID(), e.lastTriggeredRound))
+		}
+		param.Round = e.lastTriggeredRound
+		param.Reset = e.lastTriggeredResetCount
+		param.BeginHeight = e.config.LastPeriodBeginHeight()
+		param.CRS = GetCRSWithPanic(e.gov, e.lastTriggeredRound, e.logger)
+		param.Config = GetConfigWithPanic(e.gov, e.lastTriggeredRound, e.logger)
+		e.logger.Info("new RoundEvent triggered",
+			"round", e.lastTriggeredRound,
+			"reset", e.lastTriggeredResetCount,
+			"begin-height", e.config.LastPeriodBeginHeight(),
+			"crs", param.CRS.String()[:6],
+		)
+	}()
+	// Make sure current last config covers the blockHeight.
+	if !e.config.Contains(blockHeight) {
+		panic(ErrUnmatchedBlockHeightWithGov{
+			round:       e.lastTriggeredRound,
+			reset:       e.lastTriggeredResetCount,
+			blockHeight: blockHeight,
+		})
+	}
+	nextRound := e.lastTriggeredRound + 1
+	if nextRound >= startRound+e.roundShift {
+		// Avoid access configuration newer than last confirmed one over
+		// 'roundShift' rounds. Fullnode might crash if we access it before it
+		// knows.
+		return
+	}
+	nextCfg := GetConfigWithPanic(e.gov, nextRound, e.logger)
+	resetCount := e.gov.DKGResetCount(nextRound)
+	if resetCount > e.lastTriggeredResetCount {
+		e.lastTriggeredResetCount++
+		e.config.ExtendLength()
+		triggered = true
+		return
+	}
+	if lastDKGCheck {
+		// We know that DKG already failed, now wait for the DKG set from
+		// previous round to reset DKG and don't have to reconstruct the
+		// group public key again.
+		dkgFailed = true
+		return
+	}
+	if nextRound >= dkgDelayRound {
+		if !e.gov.IsDKGFinal(nextRound) {
+			e.logger.Debug("DKG is not final, waiting for DKG reset",
+				"round", nextRound,
+				"reset", e.lastTriggeredResetCount)
+			return
+		}
+		if _, err := typesDKG.NewGroupPublicKey(
+			nextRound,
+			e.gov.DKGMasterPublicKeys(nextRound),
+			e.gov.DKGComplaints(nextRound),
+			GetDKGThreshold(nextCfg)); err != nil {
+			e.logger.Debug(
+				"group public key setup failed, waiting for DKG reset",
+				"round", nextRound,
+				"reset", e.lastTriggeredResetCount)
+			dkgFailed = true
+			return
+		}
+	}
+	// The DKG set for next round is well prepared.
+	e.lastTriggeredRound = nextRound
+	e.lastTriggeredResetCount = 0
+	rCfg := RoundBasedConfig{}
+	rCfg.SetupRoundBasedFields(nextRound, nextCfg)
+	rCfg.AppendTo(e.config)
+	e.config = rCfg
+	triggered = true
+	return
+}
+
+// Stop the event source and block until last trigger returns.
+func (e *RoundEvent) Stop() {
+	e.ctxCancel()
+}
+
+// LastPeriod returns block height related info of the last period, including
+// begin height and round length.
+func (e *RoundEvent) LastPeriod() (begin uint64, length uint64) {
+	e.lock.Lock()
+	defer e.lock.Unlock()
+	begin = e.config.LastPeriodBeginHeight()
+	length = e.config.RoundEndHeight() - e.config.LastPeriodBeginHeight()
+	return
+}