default to 0 if generating output

Author: IanButterworth

src/jloptions.c

@@ -624,8 +624,11 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
         case 't': // threads
             errno = 0;
             jl_options.nthreadpools = 2;
-            // By default, main threads = -1 (== "auto"), interactive = 1
-            long nthreads = -1, nthreadsi = 1;
+            // By default:
+            // default threads = -1 (== "auto")
+            long nthreads = -1;
+            // interactive threads = 1, or 0 if generating output
+            long nthreadsi jl_generating_output() ? 0 : 1;
 
             if (!strncmp(optarg, "auto", 4)) {
                 jl_options.nthreads = -1;

src/threading.c

@@ -698,7 +698,8 @@ void jl_init_threading(void)
     // and `jl_n_threads_per_pool`.
     jl_n_threadpools = 2;
     int16_t nthreads = JULIA_NUM_THREADS;
-    int16_t nthreadsi = 1;
+    // if generating output default to 0 interactive threads, otherwise default to 1
+    int16_t nthreadsi = jl_generating_output() ? 0 : 1;
     char *endptr, *endptri;
 
     if (jl_options.nthreads != 0) { // --threads specified