Special, for-tests-only, mode with atomics emulated by a mutex-locked variable - useful for finding atomics congestions

configure.ac

@@ -132,6 +132,27 @@ AS_IF([test "$enable_fuzzing" = "afl"],
 			 [AC_MSG_ERROR([set CC=afl-<gcc|clang> when --enable-fuzzing=afl is used])])
       ])
 
+AC_ARG_ENABLE(mutex_atomics,
+	      AS_HELP_STRING([--enable-mutex-atomics],
+		             [emulate atomics by mutex-locked variables, useful for debugging
+				[default=no]]),
+	      [],
+	      [enable_mutex_atomics=no])
+
+AC_MSG_CHECKING([whether to emulate atomics with mutexes])
+case "$enable_mutex_atomics" in
+yes)
+        AC_MSG_RESULT(yes)
+        AC_DEFINE(ISC_MUTEX_ATOMICS, 1, [Define to emulate atomic variables with mutexes.])
+        ;;
+no)
+        AC_MSG_RESULT(no)
+        ;;
+*)
+        AC_MSG_ERROR("--enable-mutex-atomics requires yes or no")
+        ;;
+esac
+
 #
 # Make very sure that these are the first files processed by
 # config.status, since we use the processed output as the input for