Add Runner.is_worker() helper

doc/api.rst

@@ -692,6 +692,23 @@ Runner class
 
       Return the :attr:`args` attribute.
 
+   .. method:: is_worker()
+
+      Return ``True`` in a benchmark worker process, or ``False`` in the
+      main process. Parse command line arguments if they have not been parsed
+      yet.
+
+      Worker processes re-execute the benchmark script and may skip benchmarks,
+      returning ``None``. Run all benchmarks in both the main process and
+      workers, and use this method to guard code that processes their results::
+
+         runner = pyperf.Runner()
+         benchmarks = [runner.bench_func("first", first_func),
+                       runner.bench_func("second", second_func)]
+         if not runner.is_worker():
+             suite = pyperf.BenchmarkSuite(benchmarks)
+             suite.dump("benchmarks.json")
+
    Attributes:
 
    .. attribute:: args

pyperf/_runner.py

@@ -392,6 +392,10 @@ def parse_args(self, args=None):
         self._set_args(args)
         return args
 
+    def is_worker(self):
+        """Return whether this process is a benchmark worker."""
+        return self.parse_args().worker
+
     def _cpu_affinity(self):
         cpus = self.args.affinity
         if not cpus:

pyperf/tests/test_runner.py

@@ -484,6 +484,41 @@ def test_parse_args_twice_error(self):
         with self.assertRaises(RuntimeError):
             runner.parse_args(args)
 
+    def test_is_worker(self):
+        for args, expected in (([], False), (['--worker', '-l1', '-w0'], True)):
+            for parsed in (False, True):
+                with self.subTest(args=args, parsed=parsed):
+                    pyperf.Runner._created.clear()
+                    runner = pyperf.Runner()
+                    if parsed:
+                        runner.parse_args(args)
+                    with mock.patch.object(sys, 'argv', ['benchmark.py'] + args):
+                        self.assertIs(runner.is_worker(), expected)
+                        namespace = runner.args
+                        self.assertIs(runner.is_worker(), expected)
+                        self.assertIs(runner.args, namespace)
+
+    def test_is_worker_guards_benchmark_suite(self):
+        source = textwrap.dedent('''
+            import pyperf
+
+            def noop():
+                pass
+
+            runner = pyperf.Runner(values=1, processes=1, loops=1, warmups=0)
+            benchmarks = [runner.bench_func('first', noop),
+                          runner.bench_func('second', noop)]
+            if not runner.is_worker():
+                suite = pyperf.BenchmarkSuite(benchmarks)
+                print('suite: ' + ', '.join(suite.get_benchmark_names()))
+        ''')
+        with tests.temporary_file(suffix='.py') as filename:
+            with open(filename, 'w', encoding='utf-8') as script:
+                script.write(source)
+            result = tests.get_output([sys.executable, filename, '--quiet'])
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(result.stdout.count('suite: first, second'), 1)
+
     def test_duplicated_named(self):
         def time_func(loops):
             return 1.0