gh-108753: Enhance pystats (#108754)

Statistics gathering is now off by default. Use the "-X pystats"
command line option or set the new PYTHONSTATS environment variable
to 1 to turn statistics gathering on at Python startup.

Statistics are no longer dumped at exit if statistics gathering was
off or statistics have been cleared.

Changes:

* Add PYTHONSTATS environment variable.
* sys._stats_dump() now returns False if statistics are not dumped
  because they are all equal to zero.
* Add PyConfig._pystats member.
* Add tests on sys functions and on setting PyConfig._pystats to 1.
* Add Include/cpython/pystats.h and Include/internal/pycore_pystats.h
  header files.
* Rename '_py_stats' variable to '_Py_stats'.
* Exclude Include/cpython/pystats.h from the Py_LIMITED_API.
* Move pystats.h include from object.h to Python.h.
* Add _Py_StatsOn() and _Py_StatsOff() functions. Remove
  '_py_stats_struct' variable from the API: make it static in
  specialize.c.
* Document API in Include/pystats.h and Include/cpython/pystats.h.
* Complete pystats documentation in Doc/using/configure.rst.
* Don't write "all zeros" stats: if _stats_off() and _stats_clear()
  or _stats_dump() were called.
* _PyEval_Fini() now always call _Py_PrintSpecializationStats() which
  does nothing if stats are all zeros.

Co-authored-by: Michael Droettboom <mdboom@gmail.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/Lib/test/test_embed.py b/Lib/test/test_embed.py
index 50c9f61..7f1a4e6 100644
--- a/Lib/test/test_embed.py
+++ b/Lib/test/test_embed.py
@@ -26,6 +26,7 @@ MACOS = (sys.platform == 'darwin')
 PYMEM_ALLOCATOR_NOT_SET = 0
 PYMEM_ALLOCATOR_DEBUG = 2
 PYMEM_ALLOCATOR_MALLOC = 3
+Py_STATS = hasattr(sys, '_stats_on')
 
 # _PyCoreConfig_InitCompatConfig()
 API_COMPAT = 1
@@ -512,6 +513,8 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
         'safe_path': 0,
         '_is_python_build': IGNORE_CONFIG,
     }
+    if Py_STATS:
+        CONFIG_COMPAT['_pystats'] = 0
     if MS_WINDOWS:
         CONFIG_COMPAT.update({
             'legacy_windows_stdio': 0,
@@ -895,6 +898,8 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'check_hash_pycs_mode': 'always',
             'pathconfig_warnings': 0,
         }
+        if Py_STATS:
+            config['_pystats'] = 1
         self.check_all_configs("test_init_from_config", config, preconfig,
                                api=API_COMPAT)
 
@@ -927,6 +932,8 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'safe_path': 1,
             'int_max_str_digits': 4567,
         }
+        if Py_STATS:
+            config['_pystats'] = 1
         self.check_all_configs("test_init_compat_env", config, preconfig,
                                api=API_COMPAT)
 
@@ -960,6 +967,8 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'safe_path': 1,
             'int_max_str_digits': 4567,
         }
+        if Py_STATS:
+            config['_pystats'] = 1
         self.check_all_configs("test_init_python_env", config, preconfig,
                                api=API_PYTHON)