Try to avoid being marked as a bad quorum member when we sleep for too long in SleepBeforePhase (#3245)

* Do not sleep at the last block of the phase, it's not safe

* Refactor it a bit to make it clearer what's going on here

* Stop sleeping if blocks came faster than we expected

src/llmq/quorums_dkgsessionhandler.cpp

@@ -115,6 +115,7 @@ void CDKGSessionHandler::UpdatedBlockTip(const CBlockIndex* pindexNew)
     int quorumStageInt = pindexNew->nHeight % params.dkgInterval;
     const CBlockIndex* pindexQuorum = pindexNew->GetAncestor(pindexNew->nHeight - quorumStageInt);
 
+    currentHeight = pindexNew->nHeight;
     quorumHeight = pindexQuorum->nHeight;
     quorumHash = pindexQuorum->GetBlockHash();
 
@@ -236,23 +237,44 @@ void CDKGSessionHandler::SleepBeforePhase(QuorumPhase curPhase,
         return;
     }
 
-    // expected time for a full phase
-    double phaseTime = params.dkgPhaseBlocks * Params().GetConsensus().nPowTargetSpacing * 1000;
-    // expected time per member
-    phaseTime = phaseTime / params.size;
+    // Two blocks can come very close to each other, this happens pretty regularly. We don't want to be
+    // left behind and marked as a bad member. This means that we should not count the last block of the
+    // phase as a safe one to keep sleeping, that's why we calculate the phase sleep time as a time of
+    // the full phase minus one block here.
+    double phaseSleepTime = (params.dkgPhaseBlocks - 1) * Params().GetConsensus().nPowTargetSpacing * 1000;
+    // Expected phase sleep time per member
+    double phaseSleepTimePerMember = phaseSleepTime / params.size;
     // Don't expect perfect block times and thus reduce the phase time to be on the secure side (caller chooses factor)
-    phaseTime *= randomSleepFactor;
+    double adjustedPhaseSleepTimePerMember = phaseSleepTimePerMember * randomSleepFactor;
 
-    int64_t sleepTime = (int64_t)(phaseTime * curSession->GetMyMemberIndex());
+    int64_t sleepTime = (int64_t)(adjustedPhaseSleepTimePerMember * curSession->GetMyMemberIndex());
     int64_t endTime = GetTimeMillis() + sleepTime;
+    int heightTmp{-1};
+    int heightStart{-1};
+    {
+        LOCK(cs);
+        heightTmp = heightStart = currentHeight;
+    }
     while (GetTimeMillis() < endTime) {
         if (stopRequested || ShutdownRequested()) {
             throw AbortPhaseException();
         }
-        auto p = GetPhaseAndQuorumHash();
-        if (p.first != curPhase || p.second != expectedQuorumHash) {
+        {
+            LOCK(cs);
+            if (currentHeight > heightTmp) {
+                // New block(s) just came in
+                int64_t expectedBlockTime = (currentHeight - heightStart) * Params().GetConsensus().nPowTargetSpacing * 1000;
+                if (expectedBlockTime > sleepTime) {
+                    // Blocks came faster than we expected, jump into the phase func asap
+                    break;
+                }
+                heightTmp = currentHeight;
+            }
+            if (phase != curPhase || quorumHash != expectedQuorumHash) {
+                // Smth went wrong and/or we missed quite a few blocks and it's just too late now
                 throw AbortPhaseException();
             }
+        }
         if (!runWhileWaiting()) {
             MilliSleep(100);
         }

src/llmq/quorums_dkgsessionhandler.h

@@ -107,6 +107,7 @@ private:
     CDKGSessionManager& dkgManager;
 
     QuorumPhase phase{QuorumPhase_Idle};
+    int currentHeight{-1};
     int quorumHeight{-1};
     uint256 quorumHash;
     std::shared_ptr<CDKGSession> curSession;