cs: check for SkipTimeoutCommit or wait timeout in handleTxsAvailable (#3928)

* cs: check for SkipTimeoutCommit or wait timeout in handleTxsAvailable

Previously, if create_empty_blocks was set to false, TM sometimes could
create 2 consecutive blocks without actually waiting for timeoutCommit
(1 sec. by default).

```
I[2019-08-29|07:32:43.874] Executed block                               module=state height=47 validTxs=10 invalidTxs=0
I[2019-08-29|07:32:43.876] Committed state                              module=state height=47 txs=10 appHash=F88C010000000000
I[2019-08-29|07:32:44.885] Executed block                               module=state height=48 validTxs=2 invalidTxs=0
I[2019-08-29|07:32:44.887] Committed state                              module=state height=48 txs=2 appHash=FC8C010000000000
I[2019-08-29|07:32:44.908] Executed block                               module=state height=49 validTxs=8 invalidTxs=0
I[2019-08-29|07:32:44.909] Committed state                              module=state height=49 txs=8 appHash=8C8D010000000000
I[2019-08-29|07:32:45.886] Executed block                               module=state height=50 validTxs=2 invalidTxs=0
I[2019-08-29|07:32:45.895] Committed state                              module=state height=50 txs=2 appHash=908D010000000000
I[2019-08-29|07:32:45.908] Executed block                               module=state height=51 validTxs=8 invalidTxs=0
I[2019-08-29|07:32:45.909] Committed state                              module=state height=51 txs=8 appHash=A08D010000000000
```

This commit fixes that by adding a check to handleTxsAvailable.

Fixes #3908

* update changelog

* schedule timeoutCommit if StartTime is in the future

or SkipTimeoutCommit=true && we DON'T have all the votes

* fix TestReactorCreatesBlockWhenEmptyBlocksFalse

by checking if we have LastCommit or not

* address Ethan's comments

CHANGELOG_PENDING.md

@@ -22,3 +22,5 @@ program](https://hackerone.com/tendermint).
 - [rpc] \#2010 Add NewHTTPWithClient and NewJSONRPCClientWithHTTPClient (note these and NewHTTP, NewJSONRPCClient functions panic if remote is invalid) (@gracenoah)
 
 ### BUG FIXES:
+
+- [consensus] \#3908 Wait `timeout_commit` to pass even if `create_empty_blocks` is `false`

consensus/state.go

@@ -537,7 +537,7 @@ func (cs *ConsensusState) updateToState(state sm.State) {
 		// We add timeoutCommit to allow transactions
 		// to be gathered for the first block.
 		// And alternative solution that relies on clocks:
-		//  cs.StartTime = state.LastBlockTime.Add(timeoutCommit)
+		// cs.StartTime = state.LastBlockTime.Add(timeoutCommit)
 		cs.StartTime = cs.config.Commit(tmtime.Now())
 	} else {
 		cs.StartTime = cs.config.Commit(cs.CommitTime)
@@ -756,9 +756,25 @@ func (cs *ConsensusState) handleTimeout(ti timeoutInfo, rs cstypes.RoundState) {
 func (cs *ConsensusState) handleTxsAvailable() {
 	cs.mtx.Lock()
 	defer cs.mtx.Unlock()
-	// we only need to do this for round 0
-	cs.enterNewRound(cs.Height, 0)
-	cs.enterPropose(cs.Height, 0)
+
+	// We only need to do this for round 0.
+	if cs.Round != 0 {
+		return
+	}
+
+	switch cs.Step {
+	case cstypes.RoundStepNewHeight: // timeoutCommit phase
+		if cs.needProofBlock(cs.Height) {
+			// enterPropose will be called by enterNewRound
+			return
+		}
+
+		// +1ms to ensure RoundStepNewRound timeout always happens after RoundStepNewHeight
+		timeoutCommit := cs.StartTime.Sub(tmtime.Now()) + 1*time.Millisecond
+		cs.scheduleTimeout(timeoutCommit, cs.Height, 0, cstypes.RoundStepNewRound)
+	case cstypes.RoundStepNewRound: // after timeoutCommit
+		cs.enterPropose(cs.Height, 0)
+	}
 }
 
 //-----------------------------------------------------------------------------
@@ -766,7 +782,7 @@ func (cs *ConsensusState) handleTxsAvailable() {
 // Used internally by handleTimeout and handleMsg to make state transitions
 
 // Enter: `timeoutNewHeight` by startTime (commitTime+timeoutCommit),
-// 	or, if SkipTimeout==true, after receiving all precommits from (height,round-1)
+// 	or, if SkipTimeoutCommit==true, after receiving all precommits from (height,round-1)
 // Enter: `timeoutPrecommits` after any +2/3 precommits from (height,round-1)
 // Enter: +2/3 precommits for nil at (height,round-1)
 // Enter: +2/3 prevotes any or +2/3 precommits for block or any from (height, round)