changes per code review

Author: mitzimorris

cmdstanpy/model.py

@@ -949,21 +949,33 @@ def sample(
             if (
                 force_one_process_per_chain is None
                 and not cmdstan_version_before(2, 28, info_dict)
+                and stan_threads is not None
                 and stan_threads == 'true'
             ):
                 one_process_per_chain = False
                 num_threads = parallel_chains * num_threads
                 parallel_procs = 1
-            elif (
-                force_one_process_per_chain is False
-                and cmdstan_version_before(2, 28, info_dict)
-            ):
-                get_logger().warning(
-                    'Installed version of CmdStan cannot multi-process chains, '
-                    'will run %d processes. '
-                    'Run "install_cmdstan" to upgrade to latest version.',
-                    chains,
-                )
+            if force_one_process_per_chain is False:
+                if cmdstan_version_before(2, 28, info_dict):
+                    get_logger().warning(
+                        'Installed version of CmdStan cannot multi-process '
+                        'chains, will run %d processes. '
+                        'Run "install_cmdstan" to upgrade to latest version.',
+                        chains,
+                    )
+                elif stan_threads is None or stan_threads == 'false':
+                    get_logger().warning(
+                        'Stan program not compiled for threading, '
+                        'will run %d processes. '
+                        'Recompile model and specify argument '
+                        '"cpp_options={\'STAN_THREADS\':\'TRUE\'}.',
+                        chains,
+                    )
+                else:
+                    one_process_per_chain = False
+                    num_threads = parallel_chains * num_threads
+                    parallel_procs = 1
+
             os.environ['STAN_NUM_THREADS'] = str(num_threads)
 
             if show_console: