fix: honour JULIA_NUM_THREADS

Author: Dani Pinyol

pysrc/juliacall/__init__.py

@@ -173,7 +173,8 @@ def args_from_config(config):
     CONFIG['opt_optimize'] = choice('optimize', ['0', '1', '2', '3'])[0]
     CONFIG['opt_procs'] = int_option('procs', accept_auto=True)[0]
     CONFIG['opt_sysimage'] = sysimg = path_option('sysimage', check_exists=True)[0]
-    CONFIG['opt_threads'] = option('threads', default='1')[0]
+    env_threads=os.getenv('JULIA_NUM_THREADS','1')
+    CONFIG['opt_threads'] = option('threads', default=env_threads)[0]
     CONFIG['opt_warn_overwrite'] = choice('warn_overwrite', ['yes', 'no'])[0]
     CONFIG['opt_handle_signals'] = choice('handle_signals', ['yes', 'no'])[0]
     CONFIG['opt_startup_file'] = choice('startup_file', ['yes', 'no'])[0]