Make assertions thread-safe

tests/ExtraTests/CMakeLists.txt

@@ -479,6 +479,25 @@ set_tests_properties(
     LABELS "uses-signals"
 )
 
+add_executable(Multithreading ${TESTS_DIR}/X37-Multithreading.cpp)
+target_link_libraries(Multithreading PRIVATE Catch2::Catch2WithMain)
+add_test(
+  NAME Reporters::Multithreading
+  COMMAND ${CMAKE_COMMAND} -E env $<TARGET_FILE:Multithreading>
+)
+set_tests_properties(
+    Reporters::Multithreading
+  PROPERTIES
+    PASS_REGULAR_EXPRESSION "passed"
+    FAIL_REGULAR_EXPRESSION "ThreadSanitizer"
+)
+if (NOT WIN32)
+  target_compile_options( Reporters::Multithreading
+    PUBLIC
+      $<$<OR:$<CXX_COMPILER_ID:Clang>,$<CXX_COMPILER_ID:GNU>,$<CXX_COMPILER_ID:AppleClang>>:-fsanitize=thread>
+  )
+endif()
+
 add_executable(AssertionStartingEventGoesBeforeAssertionIsEvaluated
   X20-AssertionStartingEventGoesBeforeAssertionIsEvaluated.cpp
 )

tests/ExtraTests/X37-Multithreading.cpp

@@ -0,0 +1,34 @@
+//              Copyright Catch2 Authors
+// Distributed under the Boost Software License, Version 1.0.
+//   (See accompanying file LICENSE.txt or copy at
+//        https://www.boost.org/LICENSE_1_0.txt)
+
+// SPDX-License-Identifier: BSL-1.0
+
+#include <catch2/catch_test_macros.hpp>
+#include <catch2/internal/catch_textflow.hpp>
+#include <catch2/benchmark/catch_benchmark.hpp>
+
+#include <thread>
+#include <stop_token>
+
+TEST_CASE( "ThreadAssertionTest",
+           "[Multithreading]" ) {
+    SECTION( "Basic" ) {
+        std::jthread a([] (const std::stop_token& token) {
+            while (!token.stop_requested()) {
+                FAIL_CHECK(false);
+                CHECK(true);
+            }
+        });
+        std::jthread b([] (const std::stop_token& token) {
+            while (!token.stop_requested()) {
+                FAIL_CHECK(false);
+                CHECK(true);
+            }
+        });
+        std::this_thread::sleep_for( std::chrono::milliseconds( 1'000 ) );
+        a.get_stop_source().request_stop();
+        b.get_stop_source().request_stop();
+    }
+}