Merge bitcoin/bitcoin#23880: p2p: Serialize cmpctblock at most once in NewPoWValidBlock

fa61dd4 p2p: Serialize cmpctblock at most once in NewPoWValidBlock (MarcoFalke)

Pull request description:

  Instead of serializing for each peer, serialize at most once and copy the raw data for each peer.

ACKs for top commit:
  shaavan:
    reACK fa61dd4
  theStack:
    Code-review ACK fa61dd4

Tree-SHA512: ed029aeaea67fdac8ddb865069f8166bc0dd8480418c405628e3e1a43b61161584a09a1814668bcd220602e8732e188be2bfed9242aa81bdbd92c64c702ed138

Author: MarcoFalke

src/net_processing.cpp

@@ -41,6 +41,7 @@
 #include <algorithm>
 #include <atomic>
 #include <chrono>
+#include <future>
 #include <memory>
 #include <optional>
 #include <typeinfo>
@@ -1596,6 +1597,8 @@ void PeerManagerImpl::NewPoWValidBlock(const CBlockIndex *pindex, const std::sha
 
     bool fWitnessEnabled = DeploymentActiveAt(*pindex, m_chainparams.GetConsensus(), Consensus::DEPLOYMENT_SEGWIT);
     uint256 hashBlock(pblock->GetHash());
+    const std::shared_future<CSerializedNetMsg> lazy_ser{
+        std::async(std::launch::deferred, [&] { return msgMaker.Make(NetMsgType::CMPCTBLOCK, *pcmpctblock); })};
 
     {
         LOCK(cs_most_recent_block);
@@ -1605,10 +1608,9 @@ void PeerManagerImpl::NewPoWValidBlock(const CBlockIndex *pindex, const std::sha
         fWitnessesPresentInMostRecentCompactBlock = fWitnessEnabled;
     }
 
-    m_connman.ForEachNode([this, &pcmpctblock, pindex, &msgMaker, fWitnessEnabled, &hashBlock](CNode* pnode) EXCLUSIVE_LOCKS_REQUIRED(::cs_main) {
+    m_connman.ForEachNode([this, pindex, fWitnessEnabled, &lazy_ser, &hashBlock](CNode* pnode) EXCLUSIVE_LOCKS_REQUIRED(::cs_main) {
         AssertLockHeld(::cs_main);
 
-        // TODO: Avoid the repeated-serialization here
         if (pnode->GetCommonVersion() < INVALID_CB_NO_BAN_VERSION || pnode->fDisconnect)
             return;
         ProcessBlockAvailability(pnode->GetId());
@@ -1620,7 +1622,9 @@ void PeerManagerImpl::NewPoWValidBlock(const CBlockIndex *pindex, const std::sha
 
             LogPrint(BCLog::NET, "%s sending header-and-ids %s to peer=%d\n", "PeerManager::NewPoWValidBlock",
                     hashBlock.ToString(), pnode->GetId());
-            m_connman.PushMessage(pnode, msgMaker.Make(NetMsgType::CMPCTBLOCK, *pcmpctblock));
+
+            const CSerializedNetMsg& ser_cmpctblock{lazy_ser.get()};
+            m_connman.PushMessage(pnode, CSerializedNetMsg{ser_cmpctblock.data, ser_cmpctblock.m_type});
             state.pindexBestHeaderSent = pindex;
         }
     });