tests: allow disabling threading when debugging tests

with `-threads 1`

common/threads.cc

@@ -13,6 +13,13 @@ static std::unique_ptr<tbb::global_control> tbbGlobalControl;
 
 void configureTBB(int maxthreads, bool lowPriority)
 {
+    if (tbbGlobalControl) {
+        logging::print("ignoring multiple configureTBB calls\n");
+        // only allow calling once per process, so we can disable threading in test_main.cc
+        // and further attempts to re-enable it will be ignored
+        return;
+    }
+
     tbbGlobalControl = std::unique_ptr<tbb::global_control>();
 
     if (maxthreads > 0) {

tests/test_main.cc

@@ -2,6 +2,7 @@
 #include <doctest/doctest.h>
 
 #include <common/log.hh>
+#include <common/threads.hh>
 
 int main(int argc, char **argv)
 {
@@ -10,6 +11,14 @@ int main(int argc, char **argv)
     // writing console colors within test case output breaks doctest/CLion integration
     logging::enable_color_codes = false;
 
+    // parse "-threads 1"
+    for (int i = 1; i < argc - 1; ++i) {
+        if (!strcmp("-threads", argv[i])) {
+            configureTBB(atoi(argv[i + 1]), false);
+            break;
+        }
+    }
+
     doctest::Context context;
 
     context.applyCommandLine(argc, argv);