default to 1 interactive thread, or 0 if generating output

Author: IanButterworth

src/jloptions.c

@@ -623,8 +623,13 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
             break;
         case 't': // threads
             errno = 0;
-            jl_options.nthreadpools = 1;
-            long nthreads = -1, nthreadsi = 0;
+            jl_options.nthreadpools = 2;
+            // 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;
                 if (optarg[4] == ',') {
@@ -633,10 +638,9 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
                     else {
                         errno = 0;
                         nthreadsi = strtol(&optarg[5], &endptr, 10);
-                        if (errno != 0 || endptr == &optarg[5] || *endptr != 0 || nthreadsi < 1 || nthreadsi >= INT16_MAX)
-                            jl_errorf("julia: -t,--threads=auto,<m>; m must be an integer >= 1");
+                        if (errno != 0 || endptr == &optarg[5] || *endptr != 0 || nthreadsi < 0 || nthreadsi >= INT16_MAX)
+                            jl_errorf("julia: -t,--threads=auto,<m>; m must be an integer >= 0");
                     }
-                    jl_options.nthreadpools++;
                 }
             }
             else {
@@ -650,17 +654,18 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
                         errno = 0;
                         char *endptri;
                         nthreadsi = strtol(&endptr[1], &endptri, 10);
-                        if (errno != 0 || endptri == &endptr[1] || *endptri != 0 || nthreadsi < 1 || nthreadsi >= INT16_MAX)
-                            jl_errorf("julia: -t,--threads=<n>,<m>; n and m must be integers >= 1");
+                        // Allow 0 for interactive
+                        if (errno != 0 || endptri == &endptr[1] || *endptri != 0 || nthreadsi < 0 || nthreadsi >= INT16_MAX)
+                            jl_errorf("julia: -t,--threads=<n>,<m>; m must be an integer ≥ 0");
+                        if (nthreadsi == 0)
+                            jl_options.nthreadpools = 1;
                     }
-                    jl_options.nthreadpools++;
                 }
                 jl_options.nthreads = nthreads + nthreadsi;
             }
             int16_t *ntpp = (int16_t *)malloc_s(jl_options.nthreadpools * sizeof(int16_t));
             ntpp[0] = (int16_t)nthreads;
-            if (jl_options.nthreadpools == 2)
-                ntpp[1] = (int16_t)nthreadsi;
+            ntpp[1] = (int16_t)nthreadsi;
             jl_options.nthreads_per_pool = ntpp;
             break;
         case 'p': // procs

src/threading.c

@@ -698,15 +698,15 @@ void jl_init_threading(void)
     // and `jl_n_threads_per_pool`.
     jl_n_threadpools = 2;
     int16_t nthreads = JULIA_NUM_THREADS;
-    int16_t nthreadsi = 0;
+    // 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
         nthreads = jl_options.nthreads_per_pool[0];
         if (nthreads < 0)
             nthreads = jl_effective_threads();
-        if (jl_options.nthreadpools == 2)
-            nthreadsi = jl_options.nthreads_per_pool[1];
+        nthreadsi = (jl_options.nthreadpools == 1) ? 0 : jl_options.nthreads_per_pool[1];
     }
     else if ((cp = getenv(NUM_THREADS_NAME))) { // ENV[NUM_THREADS_NAME] specified
         if (!strncmp(cp, "auto", 4)) {
@@ -722,13 +722,16 @@ void jl_init_threading(void)
         }
         if (*cp == ',') {
             cp++;
-            if (!strncmp(cp, "auto", 4))
+            if (!strncmp(cp, "auto", 4)) {
                 nthreadsi = 1;
+                cp += 4;
+            }
             else {
                 errno = 0;
                 nthreadsi = strtol(cp, &endptri, 10);
                 if (errno != 0 || endptri == cp || nthreadsi < 0)
-                    nthreadsi = 0;
+                    nthreadsi = 1;
+                cp = endptri;
             }
         }
     }