allow header sync from more than one peer during IBD

src/chain/chainman.cpp

@@ -474,7 +474,6 @@ void CChainManager::UnloadBlockIndex()
     pindexBestInvalid = nullptr;
     pindexBestHeader = nullptr;
     mempool.clear();
-    nSyncStarted = 0;
     mapBlocksUnlinked.clear();
     vinfoBlockFile.clear();
     nLastBlockFile = 0;

src/main.cpp

@@ -116,9 +116,6 @@ CBlockIndex *pindexBestInvalid;
  */
 std::set<CBlockIndex *, CBlockIndexWorkComparator> setBlockIndexCandidates;
 
-/** Number of nodes with fSyncStarted. */
-int nSyncStarted = 0;
-
 /** All pairs A->B, where A (or one of its ancestors) misses transactions, but B has transactions.
  * Pruned nodes may have entries where B is missing data.
  */

src/main.h

@@ -259,7 +259,6 @@ enum FlushStateMode
 };
 bool FlushStateToDisk(CValidationState &state, FlushStateMode mode);
 extern int nPreferredDownload;
-extern int nSyncStarted;
 extern int64_t nTimeBestReceived;
 extern int nPeersWithValidatedDownloads;
 

src/net/messages.cpp

@@ -140,11 +140,6 @@ void FinalizeNode(NodeId nodeid, bool &fUpdateConnectionTime)
     fUpdateConnectionTime = false;
     CNodeStateAccessor state(nodestateman, nodeid);
 
-    if (state->fSyncStarted)
-    {
-        nSyncStarted--;
-    }
-
     if (state->nMisbehavior == 0 && state->fCurrentlyConnected)
     {
         fUpdateConnectionTime = true;
@@ -2391,13 +2386,9 @@ bool SendMessages(CNode *pto, CConnman &connman)
 
     if (!nodestate->fSyncStarted && !pto->fClient && !fImporting && !fReindex)
     {
-        // Only actively request headers from a single peer, unless we're close
-        // to today.
-        if ((nSyncStarted == 0 && fFetch) ||
-            pnetMan->getChainActive()->pindexBestHeader->GetBlockTime() > GetAdjustedTime() - 24 * 60 * 60)
+        if (fFetch || pnetMan->getChainActive()->pindexBestHeader->GetBlockTime() > GetAdjustedTime() - 24 * 60 * 60)
         {
             nodestate->fSyncStarted = true;
-            nSyncStarted++;
             const CBlockIndex *pindexStart = pnetMan->getChainActive()->pindexBestHeader;
             /**
              * If possible, start at the block preceding the currently best