gh-119727: Add --single-process option to regrtest

Lib/test/libregrtest/cmdline.py

@@ -174,6 +174,7 @@ def __init__(self, **kwargs) -> None:
         self.tempdir = None
         self._add_python_opts = True
         self.xmlpath = None
+        self.sequentially = False
 
         super().__init__(**kwargs)
 
@@ -307,6 +308,10 @@ def _create_parser():
     group.add_argument('-j', '--multiprocess', metavar='PROCESSES',
                        dest='use_mp', type=int,
                        help='run PROCESSES processes at once')
+    group.add_argument('--sequentially', action='store_true',
+                       help='always run all tests sequentially, '
+                            'ignore -jN option, '
+                            'and failed tests are also rerun sequentially')
     group.add_argument('-T', '--coverage', action='store_true',
                        dest='trace',
                        help='turn on code coverage tracing using the trace '

Lib/test/libregrtest/main.py

@@ -89,7 +89,10 @@ def __init__(self, ns: Namespace, _add_python_opts: bool = False):
         self.cmdline_args: TestList = ns.args
 
         # Workers
-        if ns.use_mp is None:
+        self.sequentially: bool = ns.sequentially
+        if self.sequentially:
+            num_workers = 0  # run sequentially
+        elif ns.use_mp is None:
             num_workers = 0  # run sequentially
         elif ns.use_mp <= 0:
             num_workers = -1  # use the number of CPUs
@@ -236,7 +239,7 @@ def list_tests(tests: TestTuple):
 
     def _rerun_failed_tests(self, runtests: RunTests):
         # Configure the runner to re-run tests
-        if self.num_workers == 0:
+        if self.num_workers == 0 and not self.sequentially:
             # Always run tests in fresh processes to have more deterministic
             # initial state. Don't re-run tests in parallel but limit to a
             # single worker process to have side effects (on the system load
@@ -246,7 +249,6 @@ def _rerun_failed_tests(self, runtests: RunTests):
         tests, match_tests_dict = self.results.prepare_rerun()
 
         # Re-run failed tests
-        self.log(f"Re-running {len(tests)} failed tests in verbose mode in subprocesses")
         runtests = runtests.copy(
             tests=tests,
             rerun=True,
@@ -256,7 +258,15 @@ def _rerun_failed_tests(self, runtests: RunTests):
             match_tests_dict=match_tests_dict,
             output_on_failure=False)
         self.logger.set_tests(runtests)
-        self._run_tests_mp(runtests, self.num_workers)
+
+        msg = f"Re-running {len(tests)} failed tests in verbose mode"
+        if not self.sequentially:
+            msg = f"{msg} in subprocesses"
+            self.log(msg)
+            self._run_tests_mp(runtests, self.num_workers)
+        else:
+            self.log(msg)
+            self.run_tests_sequentially(runtests)
         return runtests
 
     def rerun_failed_tests(self, runtests: RunTests):
@@ -599,7 +609,7 @@ def _add_cross_compile_opts(self, regrtest_opts):
             keep_environ = True
 
         if cross_compile and hostrunner:
-            if self.num_workers == 0:
+            if self.num_workers == 0 and not self.sequentially:
                 # For now use only two cores for cross-compiled builds;
                 # hostrunner can be expensive.
                 regrtest_opts.extend(['-j', '2'])

Lib/test/libregrtest/worker.py

@@ -14,9 +14,9 @@
 
 
 USE_PROCESS_GROUP = (hasattr(os, "setsid") and hasattr(os, "killpg"))
-NEED_TTY = set('''
-    test_ioctl
-'''.split())
+NEED_TTY = {
+    'test_ioctl',
+}
 
 
 def create_worker_process(runtests: WorkerRunTests, output_fd: int,

Lib/test/test_regrtest.py

@@ -473,6 +473,13 @@ def test_verbose3_huntrleaks(self):
         self.assertEqual(regrtest.hunt_refleak.runs, 10)
         self.assertFalse(regrtest.output_on_failure)
 
+    def test_sequentially(self):
+        args = ['-j2', '--sequentially']
+        with support.captured_stderr():
+            regrtest = self.create_regrtest(args)
+        self.assertEqual(regrtest.num_workers, 0)
+        self.assertTrue(regrtest.sequentially)
+
 
 @dataclasses.dataclass(slots=True)
 class Rerun:

Misc/NEWS.d/next/Tests/2024-05-29-15-28-08.gh-issue-119727.dVkaZM.rst

@@ -0,0 +1,2 @@
+Add ``--sequentially`` command line option to Python test runner (regrtest).
+Patch by Victor Stinner.