diff --git a/contributors.txt b/contributors.txt
index 8ffda95f7b..ac8c193d94 100644
--- a/contributors.txt
+++ b/contributors.txt
@@ -317,4 +317,4 @@ YYYY/MM/DD, github id, Full name, email
 2021/09/08, jmcken8, Joel McKenzie, joel.b.mckenzie@gmail.com
 2021/09/23, skalt, Steven Kalt, kalt.steven@gmail.com
 2021/10/10, tools4origins, Erwan Guyomarc'h, contact@erwan-guyomarch.fr
-2021/10/25, jcking, Justin King, jcking@google.com
\ No newline at end of file
+2021/10/19, jcking, Justin King, jcking@google.com
\ No newline at end of file
diff --git a/runtime/Cpp/runtime/src/atn/ATNDeserializationOptions.cpp b/runtime/Cpp/runtime/src/atn/ATNDeserializationOptions.cpp
index a406c4e135..d070cd9d61 100755
--- a/runtime/Cpp/runtime/src/atn/ATNDeserializationOptions.cpp
+++ b/runtime/Cpp/runtime/src/atn/ATNDeserializationOptions.cpp
@@ -7,7 +7,7 @@
 
 using namespace antlr4::atn;
 
-ATNDeserializationOptions ATNDeserializationOptions::defaultOptions;
+const ATNDeserializationOptions ATNDeserializationOptions::defaultOptions;
 
 ATNDeserializationOptions::ATNDeserializationOptions() {
   InitializeInstanceFields();
diff --git a/runtime/Cpp/runtime/src/atn/ATNDeserializationOptions.h b/runtime/Cpp/runtime/src/atn/ATNDeserializationOptions.h
index 66aa37da5f..f03bdb39ad 100755
--- a/runtime/Cpp/runtime/src/atn/ATNDeserializationOptions.h
+++ b/runtime/Cpp/runtime/src/atn/ATNDeserializationOptions.h
@@ -12,7 +12,7 @@ namespace atn {
 
   class ANTLR4CPP_PUBLIC ATNDeserializationOptions {
   private:
-    static ATNDeserializationOptions defaultOptions;
+    static const ATNDeserializationOptions defaultOptions;
 
     bool readOnly;
     bool verifyATN;
diff --git a/runtime/Cpp/runtime/src/atn/LexerATNSimulator.cpp b/runtime/Cpp/runtime/src/atn/LexerATNSimulator.cpp
index 827c3d59f1..381351a95a 100755
--- a/runtime/Cpp/runtime/src/atn/LexerATNSimulator.cpp
+++ b/runtime/Cpp/runtime/src/atn/LexerATNSimulator.cpp
@@ -47,7 +47,7 @@ void LexerATNSimulator::SimState::InitializeInstanceFields() {
   charPos = INVALID_INDEX;
 }
 
-int LexerATNSimulator::match_calls = 0;
+std::atomic<int> LexerATNSimulator::match_calls(0);
 
 
 LexerATNSimulator::LexerATNSimulator(const ATN &atn, std::vector<dfa::DFA> &decisionToDFA,
@@ -69,7 +69,7 @@ void LexerATNSimulator::copyState(LexerATNSimulator *simulator) {
 }
 
 size_t LexerATNSimulator::match(CharStream *input, size_t mode) {
-  match_calls++;
+  match_calls.fetch_add(1, std::memory_order_relaxed);
   _mode = mode;
   ssize_t mark = input->mark();
 
diff --git a/runtime/Cpp/runtime/src/atn/LexerATNSimulator.h b/runtime/Cpp/runtime/src/atn/LexerATNSimulator.h
index c050d516c0..cfe2d913be 100755
--- a/runtime/Cpp/runtime/src/atn/LexerATNSimulator.h
+++ b/runtime/Cpp/runtime/src/atn/LexerATNSimulator.h
@@ -5,6 +5,8 @@
 
 #pragma once
 
+#include <atomic>
+
 #include "atn/ATNSimulator.h"
 #include "atn/LexerATNConfig.h"
 #include "atn/ATNConfigSet.h"
@@ -89,7 +91,7 @@ namespace atn {
     SimState _prevAccept;
 
   public:
-    static int match_calls;
+    static std::atomic<int> match_calls;
 
     LexerATNSimulator(const ATN &atn, std::vector<dfa::DFA> &decisionToDFA, PredictionContextCache &sharedContextCache);
     LexerATNSimulator(Lexer *recog, const ATN &atn, std::vector<dfa::DFA> &decisionToDFA, PredictionContextCache &sharedContextCache);
diff --git a/runtime/Cpp/runtime/src/atn/PredictionContext.cpp b/runtime/Cpp/runtime/src/atn/PredictionContext.cpp
index 860a18056d..126d403fe4 100755
--- a/runtime/Cpp/runtime/src/atn/PredictionContext.cpp
+++ b/runtime/Cpp/runtime/src/atn/PredictionContext.cpp
@@ -20,12 +20,12 @@ using namespace antlr4::atn;
 
 using namespace antlrcpp;
 
-size_t PredictionContext::globalNodeCount = 0;
+std::atomic<size_t> PredictionContext::globalNodeCount(0);
 const Ref<PredictionContext> PredictionContext::EMPTY = std::make_shared<EmptyPredictionContext>();
 
 //----------------- PredictionContext ----------------------------------------------------------------------------------
 
-PredictionContext::PredictionContext(size_t cachedHashCode) : id(globalNodeCount++), cachedHashCode(cachedHashCode)  {
+PredictionContext::PredictionContext(size_t cachedHashCode) : id(globalNodeCount.fetch_add(1, std::memory_order_relaxed)), cachedHashCode(cachedHashCode)  {
 }
 
 PredictionContext::~PredictionContext() {
diff --git a/runtime/Cpp/runtime/src/atn/PredictionContext.h b/runtime/Cpp/runtime/src/atn/PredictionContext.h
index e8dfc23f77..887c53ba50 100755
--- a/runtime/Cpp/runtime/src/atn/PredictionContext.h
+++ b/runtime/Cpp/runtime/src/atn/PredictionContext.h
@@ -5,6 +5,8 @@
 
 #pragma once
 
+#include <atomic>
+
 #include "Recognizer.h"
 #include "atn/ATN.h"
 #include "atn/ATNState.h"
@@ -48,7 +50,7 @@ namespace atn {
 #endif
 
   public:
-    static size_t globalNodeCount;
+    static std::atomic<size_t> globalNodeCount;
     const size_t id;
 
     /// <summary>