Remove g_parallel_script_checks global variable

This variable is not really used by our codebase -- we always use the
CCheckQueue, even if no parallel threads are specified (in that case we
use it with the foreground thread).  So this variable had no meaning in
our codebase.

This undoes some of the core backport #17342

src/bench/checkqueue.cpp

@@ -41,7 +41,7 @@ static void CCheckQueueSpeedPrevectorJob(benchmark::State &state) {
         void swap(PrevectorJob &x) { p.swap(x.p); };
     };
     CCheckQueue<PrevectorJob> queue{QUEUE_BATCH_SIZE};
-    queue.StartWorkerThreads(std::max(MIN_CORES, GetNumCores()));
+    queue.StartWorkerThreads(std::max(MIN_CORES, GetNumCores()) - 1);
     while (state.KeepRunning()) {
         // Make insecure_rand here so that each iteration is identical.
         FastRandomContext insecure_rand(true);

src/init.cpp

@@ -2105,7 +2105,6 @@ bool AppInitMain(Config &config, RPCServer &rpcServer,
 
     LogPrintf("Script verification uses %d additional threads\n", script_threads);
     if (script_threads >= 1) {
-        g_parallel_script_checks = true;
         StartScriptCheckWorkerThreads(script_threads);
     }
 

src/test/setup_common.cpp

@@ -122,10 +122,9 @@ TestingSetup::TestingSetup(const std::string &chainName)
         }
     }
 
-    // Start script-checking threads. Set g_parallel_script_checks to true so they are used.
+    // Start script-checking threads
     constexpr int script_check_threads = 2;
     StartScriptCheckWorkerThreads(script_check_threads);
-    g_parallel_script_checks = true;
 
     g_banman =
         std::make_unique<BanMan>(GetDataDir() / "banlist.dat", chainparams,

src/validation.cpp

@@ -260,7 +260,6 @@ CBlockIndex *pindexBestHeader = nullptr;
 Mutex g_best_block_mutex;
 std::condition_variable g_best_block_cv;
 uint256 g_best_block;
-bool g_parallel_script_checks{false};
 std::atomic_bool fImporting(false);
 std::atomic_bool fReindex(false);
 bool fHavePruned = false;
@@ -1892,7 +1891,7 @@ bool CChainState::ConnectBlock(const CBlock &block, CValidationState &state,
     CBlockUndo blockundo;
     blockundo.vtxundo.resize(block.vtx.size() - 1);
 
-    CCheckQueueControl<CScriptCheck> control(fScriptChecks && g_parallel_script_checks ? &scriptcheckqueue : nullptr);
+    CCheckQueueControl<CScriptCheck> control(fScriptChecks ? &scriptcheckqueue : nullptr);
 
     // Add all outputs
     try {

src/validation.h

@@ -207,10 +207,6 @@ extern uint256 g_best_block;
 extern std::atomic_bool fImporting;
 extern std::atomic_bool fReindex;
 extern bool fIsBareMultisigStd;
-/** Whether there are dedicated script-checking threads running.
- * False indicates all script checking is done on the main threadMessageHandler thread.
- */
-extern bool g_parallel_script_checks;
 extern bool fRequireStandard;
 extern bool fCheckBlockIndex;
 extern bool fCheckpointsEnabled;