raft: refactor election function, separate response parsing

src/raft/RaftCommon.hh

@@ -230,7 +230,6 @@ struct RaftVoteResponse {
 
     return ret;
   }
-
 };
 
 inline size_t calculateQuorumSize(size_t members) {

src/raft/RaftUtils.cc

@@ -32,6 +32,55 @@
 
 namespace quarkdb {
 
+static ElectionSingleTally parseSingleTally(std::future<qclient::redisReplyPtr> &fut, std::chrono::steady_clock::time_point deadline) {
+  ElectionSingleTally singleTally;
+
+  if(fut.wait_until(deadline) != std::future_status::ready) {
+    singleTally.timeout = true;
+    singleTally.error = false;
+    return singleTally;
+  }
+
+  redisReplyPtr reply = fut.get();
+  if(reply == nullptr || !RaftParser::voteResponse(reply, singleTally.resp)) {
+    singleTally.timeout = false;
+    singleTally.error = true;
+    return singleTally;
+  }
+
+  singleTally.timeout = false;
+  singleTally.error = false;
+  return singleTally;
+}
+
+static ElectionTally makeElectionTally(RaftVoteRequest votereq, const std::vector<RaftServer> &nodes, const RaftContactDetails &contactDetails) {
+  qdb_info("Starting election round for term " << votereq.term);
+
+  std::vector<std::unique_ptr<RaftTalker>> talkers;
+  std::map<RaftServer, std::future<redisReplyPtr>> futures;
+
+  for(const RaftServer &node : nodes) {
+    if(node != votereq.candidate) {
+      talkers.emplace_back(new RaftTalker(node, contactDetails, "internal-vote-request"));
+      futures[node] = talkers.back()->requestVote(votereq);
+    }
+  }
+
+  std::chrono::steady_clock::time_point now = std::chrono::steady_clock::now();
+  std::chrono::steady_clock::time_point deadline = now + contactDetails.getRaftTimeouts().getHeartbeatInterval()*2;
+
+  qdb_info("Vote requests have been sent off, will allow a window of "
+    << contactDetails.getRaftTimeouts().getLow().count() << "ms to receive replies.");
+
+  ElectionTally tally;
+  for(auto it = futures.begin(); it != futures.end(); it++) {
+    tally[it->first] = parseSingleTally(it->second, deadline);
+  }
+
+  qdb_info("No longer accepting replies to vote requests, time to make a tally.");
+  return tally;
+}
+
 ElectionOutcome RaftElection::perform(RaftVoteRequest votereq, RaftState &state, RaftLease &lease, const RaftContactDetails &contactDetails) {
   if(!votereq.candidate.empty()) {
     qdb_throw("candidate member of votereq must be empty, it is filled out by this function");
@@ -55,63 +104,40 @@ ElectionOutcome RaftElection::perform(RaftVoteRequest votereq, RaftState &state,
     return ElectionOutcome::kNotElected;
   }
 
-  qdb_info(state.getMyself().toString() << ": Starting election round for term " << votereq.term);
-  std::vector<std::unique_ptr<RaftTalker>> talkers;
 
   std::chrono::steady_clock::time_point broadcastTimepoint = std::chrono::steady_clock::now();
-
-  std::vector<std::future<redisReplyPtr>> futures;
-  for(const RaftServer &node : state.getNodes()) {
-    if(node != state.getMyself()) {
-      talkers.emplace_back(new RaftTalker(node, contactDetails, "internal-vote-request"));
-      futures.push_back(talkers.back()->requestVote(votereq));
-    }
-  }
-
-  std::vector<redisReplyPtr> replies;
-  std::chrono::steady_clock::time_point now = std::chrono::steady_clock::now();
-  std::chrono::steady_clock::time_point deadline = now + contactDetails.getRaftTimeouts().getHeartbeatInterval()*2;
-
-  qdb_info(state.getMyself().toString() <<  ": Vote requests have been sent off, will allow a window of "
-    << contactDetails.getRaftTimeouts().getLow().count() << "ms to receive replies.");
-
-  for(size_t i = 0; i < futures.size(); i++) {
-    if(futures[i].wait_until(deadline) == std::future_status::ready) {
-      redisReplyPtr reply = futures[i].get();
-      if(reply != nullptr) replies.push_back(reply);
-    }
-  }
-
-  qdb_info("No longer accepting replies to vote requests, time to make a tally.");
+  ElectionTally tally = makeElectionTally(votereq, state.getNodes(), contactDetails);
 
   size_t granted = 0;
   size_t refused = 0;
   size_t veto = 0;
+  size_t replies = 0;
 
-  for(size_t i = 0; i < replies.size(); i++) {
-    RaftVoteResponse resp;
-    if(!RaftParser::voteResponse(replies[i], resp)) {
-      qdb_critical("unable to parse a vote response, ignoring");
+  for(auto it = tally.begin(); it != tally.end(); it++) {
+    ElectionSingleTally singleTally = it->second;
+
+    if(singleTally.timeout || singleTally.error) {
+      continue;
+    }
+
+    if(singleTally.resp.vote == RaftVote::GRANTED) {
+      lease.getHandler(it->first).heartbeat(broadcastTimepoint);
+      granted++;
     }
-    else {
-      if(resp.vote == RaftVote::GRANTED) {
-        lease.getHandler(talkers[i]->getServer()).heartbeat(broadcastTimepoint);
-        granted++;
-      }
-      else if(resp.vote == RaftVote::REFUSED) {
-        refused++;
-      }
-      else if(resp.vote == RaftVote::VETO) {
-        veto++;
-      }
-      state.observed(resp.term, {});
+    else if(singleTally.resp.vote == RaftVote::REFUSED) {
+      refused++;
     }
+    else if(singleTally.resp.vote == RaftVote::VETO) {
+      veto++;
+    }
+
+    state.observed(singleTally.resp.term, {});
   }
 
-  talkers.clear();
+  replies = granted + refused + veto;
 
-  std::string description = SSTR("Contacted " << futures.size() << " nodes, received "
-    << replies.size() << " replies with a tally of " << granted << " positive votes, " << refused << " refused votes, and " << veto << " vetoes.");
+  std::string description = SSTR("Contacted " << tally.size() << " nodes, received "
+    << replies << " replies with a tally of " << granted << " positive votes, " << refused << " refused votes, and " << veto << " vetoes.");
 
   if(granted+1 >= (state.getNodes().size() / 2)+1 ) {
     if(veto > 0) {

src/raft/RaftUtils.hh

@@ -55,6 +55,14 @@ enum class ElectionOutcome {
   kVetoed
 };
 
+struct ElectionSingleTally {
+  bool timeout;
+  bool error;
+  RaftVoteResponse resp;
+};
+
+using ElectionTally = std::map<RaftServer, ElectionSingleTally>;
+
 class RaftElection {
 public:
   static ElectionOutcome perform(RaftVoteRequest votereq, RaftState &state, RaftLease &lease, const RaftContactDetails &contactDetails);