validation: only create a CCheckQueueControl if it's actually going to be used

This will allow CCheckQueueControl to require a CCheckQueue.

Author: theuni

src/validation.cpp

@@ -2611,7 +2611,9 @@ bool Chainstate::ConnectBlock(const CBlock& block, BlockValidationState& state,
     // in multiple threads). Preallocate the vector size so a new allocation
     // doesn't invalidate pointers into the vector, and keep txsdata in scope
     // for as long as `control`.
-    CCheckQueueControl<CScriptCheck> control(fScriptChecks && parallel_script_checks ? &m_chainman.GetCheckQueue() : nullptr);
+    std::optional<CCheckQueueControl<CScriptCheck>> control;
+    if (fScriptChecks && parallel_script_checks) control.emplace(&m_chainman.GetCheckQueue());
+
     std::vector<PrecomputedTransactionData> txsdata(block.vtx.size());
 
     std::vector<int> prevheights;
@@ -2680,7 +2682,7 @@ bool Chainstate::ConnectBlock(const CBlock& block, BlockValidationState& state,
                               tx_state.GetRejectReason(), tx_state.GetDebugMessage());
                 break;
             }
-            control.Add(std::move(vChecks));
+            if (control) control->Add(std::move(vChecks));
         }
 
         CTxUndo undoDummy;
@@ -2702,10 +2704,11 @@ bool Chainstate::ConnectBlock(const CBlock& block, BlockValidationState& state,
         state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, "bad-cb-amount",
                       strprintf("coinbase pays too much (actual=%d vs limit=%d)", block.vtx[0]->GetValueOut(), blockReward));
     }
-
-    auto parallel_result = control.Complete();
-    if (parallel_result.has_value() && state.IsValid()) {
-        state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, strprintf("mandatory-script-verify-flag-failed (%s)", ScriptErrorString(parallel_result->first)), parallel_result->second);
+    if (control) {
+        auto parallel_result = control->Complete();
+        if (parallel_result.has_value() && state.IsValid()) {
+            state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, strprintf("mandatory-script-verify-flag-failed (%s)", ScriptErrorString(parallel_result->first)), parallel_result->second);
+        }
     }
     if (!state.IsValid()) {
         LogInfo("Block validation error: %s", state.ToString());