Allow SendMessages to run partially without cs_main

SendMessages() tries to acquire a cs_main lock now, but this isn't nessecary
for much of its functionality. Move those parts out of the locked section,
so they can always be performed, and we hold cs_main for a shorter time.

src/main.cpp

@@ -4134,8 +4134,7 @@ bool ProcessMessages(CNode* pfrom)
 
 bool SendMessages(CNode* pto, bool fSendTrickle)
 {
-    TRY_LOCK(cs_main, lockMain);
+    {
-    if (lockMain) {
         // Don't send anything until we get their version message
         if (pto->nVersion == 0)
             return true;
@@ -4170,20 +4169,6 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
             }
         }
 
-        // Start block sync
-        if (pto->fStartSync && !fImporting && !fReindex) {
-            pto->fStartSync = false;
-            PushGetBlocks(pto, chainActive.Tip(), uint256(0));
-        }
-
-        // Resend wallet transactions that haven't gotten in a block yet
-        // Except during reindex, importing and IBD, when old wallet
-        // transactions become unconfirmed and spams other nodes.
-        if (!fReindex && !fImporting && !IsInitialBlockDownload())
-        {
-            ResendWalletTransactions();
-        }
-
         // Address refresh broadcast
         static int64 nLastRebroadcast;
         if (!IsInitialBlockDownload() && (GetTime() - nLastRebroadcast > 24 * 60 * 60))
@@ -4234,6 +4219,23 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
                 pto->PushMessage("addr", vAddr);
         }
 
+        TRY_LOCK(cs_main, lockMain);
+        if (!lockMain)
+            return true;
+
+        // Start block sync
+        if (pto->fStartSync && !fImporting && !fReindex) {
+            pto->fStartSync = false;
+            PushGetBlocks(pto, chainActive.Tip(), uint256(0));
+        }
+
+        // Resend wallet transactions that haven't gotten in a block yet
+        // Except during reindex, importing and IBD, when old wallet
+        // transactions become unconfirmed and spams other nodes.
+        if (!fReindex && !fImporting && !IsInitialBlockDownload())
+        {
+            ResendWalletTransactions();
+        }
 
         //
         // Message: inventory