728 Implement PreCommit Stage (#749)

# Description

- If ```round.isCompletable() = true``` or timer ```Time >= t + 4 * T```
is expires -> end pre-commit stage
- end() method waits ```round.getGrandpaGhost()``` to have a value
before proceeding to the next stage
- Once GrandpaGhost is available, a vote message is broadcast
- ```isCompleted``` field is added to ```GrandpaRound``` that is
updated, when ```findGrandpaGhost``` is executed and the previous method
for checking if the round is completable is renamed to
```checkIfCompletable```

Fixes #728

---------

Co-authored-by: Hristiyan Mitov <[email protected]>
Co-authored-by: Hristiyan Mitov <[email protected]>

src/main/java/com/limechain/grandpa/round/CompletedStage.java

@@ -8,7 +8,7 @@ public class CompletedStage implements StageState {
     @Override
     public void start(GrandpaRound round) {
         round.setOnFinalizeHandler(null);
-        round.getOnStageTimerHandler().shutdown();
+        round.clearOnStageTimerHandler();
         end(round);
     }
 

src/main/java/com/limechain/grandpa/round/GrandpaRound.java

@@ -103,6 +103,12 @@ public class GrandpaRound {
     @Nullable
     private Vote preCommitChoice;
 
+    /**
+     * Updated when the Grandpa Ghost is calculated.<BR>
+     * Default value is false.
+     */
+    private boolean isCompletable;
+
     private Map<Hash256, SignedVote> preVotes = new ConcurrentHashMap<>();
     private Map<Hash256, SignedVote> preCommits = new ConcurrentHashMap<>();
     private Vote primaryVote;
@@ -248,7 +254,7 @@ private boolean isFinalizable() {
      *
      * @return if the current round is completable
      */
-    private boolean isCompletable() {
+    public boolean checkIfCompletable() {
 
         Map<Vote, Long> votes = getDirectVotes(SubRound.PRE_COMMIT);
         long votesCount = votes.values().stream()
@@ -350,7 +356,7 @@ private BlockHeader findBestFinalCandidate() {
      *
      * @return GRANDPA GHOST block as a vote
      */
-    private BlockHeader findGrandpaGhost() {
+    public BlockHeader findGrandpaGhost() {
 
         if (roundNumber.equals(BigInteger.ZERO)) {
             return lastFinalizedBlock;
@@ -362,10 +368,11 @@ private BlockHeader findGrandpaGhost() {
             throw new GhostExecutionException("GHOST not found");
         }
 
-        BlockHeader grandpaGhost = selectBlockWithMostVotes(blocks, getPrevBestFinalCandidate());
-        this.grandpaGhost = grandpaGhost;
+        BlockHeader result = selectBlockWithMostVotes(blocks, getPrevBestFinalCandidate());
+        this.grandpaGhost = result;
+        this.isCompletable = checkIfCompletable();
 
-        return grandpaGhost;
+        return result;
     }
 
     /**
@@ -650,4 +657,11 @@ public void broadcastCommitMessage() {
 
         peerMessageCoordinator.sendCommitMessageToPeers(commitMessage);
     }
+
+    public void clearOnStageTimerHandler() {
+        if (onStageTimerHandler != null && onStageTimerHandler.isShutdown()) {
+            onStageTimerHandler.shutdown();
+            onStageTimerHandler = null;
+        }
+    }
 }

src/main/java/com/limechain/grandpa/round/PreCommitStage.java

@@ -1,13 +1,51 @@
 package com.limechain.grandpa.round;
 
+import com.limechain.exception.grandpa.GrandpaGenericException;
+import com.limechain.grandpa.vote.SubRound;
+import com.limechain.grandpa.vote.Vote;
+import lombok.extern.java.Log;
+
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
+@Log
 public class PreCommitStage implements StageState {
 
     @Override
     public void start(GrandpaRound round) {
+        log.fine(String.format("Round %d started pre-commit stage.", round.getRoundNumber()));
+
+        if (round.isCompletable()) {
+            end(round);
+            return;
+        }
+
+        long timeElapsed = System.currentTimeMillis() - round.getStartTime().toEpochMilli();
+        long timeRemaining = (4 * GrandpaRound.DURATION) - timeElapsed;
+
+        round.setOnStageTimerHandler(Executors.newScheduledThreadPool(1));
+        round.getOnStageTimerHandler().schedule(() -> {
+            log.fine(String.format("Round %d timer triggered.", round.getRoundNumber()));
+            end(round);
+        }, timeRemaining, TimeUnit.MILLISECONDS);
     }
 
     @Override
     public void end(GrandpaRound round) {
-    }
-}
 
+        round.clearOnStageTimerHandler();
+
+        try {
+
+            Vote grandpaGhost = Vote.fromBlockHeader(round.getGrandpaGhost());
+            log.fine(String.format("Round %d ended pre-commit stage.", round.getRoundNumber()));
+
+            round.broadcastVoteMessage(grandpaGhost, SubRound.PRE_COMMIT);
+            round.setState(new FinalizeStage());
+            round.getState().start(round);
+
+        } catch (GrandpaGenericException e) {
+            log.fine(String.format("Round %d cannot end now: %s", round.getRoundNumber(), e.getMessage()));
+        }
+    }
+}