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>

2 files changed, 30 insertions, 9 deletions

diff --git a/Include/internal/pycore_code.h b/Include/internal/pycore_code.h
index f5127a8..7c66290 100644
--- a/Include/internal/pycore_code.h
+++ b/Include/internal/pycore_code.h
@@ -268,17 +268,17 @@ extern int _PyStaticCode_Init(PyCodeObject *co);
 
 #ifdef Py_STATS
 
-#define STAT_INC(opname, name) do { if (_py_stats) _py_stats->opcode_stats[opname].specialization.name++; } while (0)
-#define STAT_DEC(opname, name) do { if (_py_stats) _py_stats->opcode_stats[opname].specialization.name--; } while (0)
-#define OPCODE_EXE_INC(opname) do { if (_py_stats) _py_stats->opcode_stats[opname].execution_count++; } while (0)
-#define CALL_STAT_INC(name) do { if (_py_stats) _py_stats->call_stats.name++; } while (0)
-#define OBJECT_STAT_INC(name) do { if (_py_stats) _py_stats->object_stats.name++; } while (0)
+#define STAT_INC(opname, name) do { if (_Py_stats) _Py_stats->opcode_stats[opname].specialization.name++; } while (0)
+#define STAT_DEC(opname, name) do { if (_Py_stats) _Py_stats->opcode_stats[opname].specialization.name--; } while (0)
+#define OPCODE_EXE_INC(opname) do { if (_Py_stats) _Py_stats->opcode_stats[opname].execution_count++; } while (0)
+#define CALL_STAT_INC(name) do { if (_Py_stats) _Py_stats->call_stats.name++; } while (0)
+#define OBJECT_STAT_INC(name) do { if (_Py_stats) _Py_stats->object_stats.name++; } while (0)
 #define OBJECT_STAT_INC_COND(name, cond) \
-    do { if (_py_stats && cond) _py_stats->object_stats.name++; } while (0)
-#define EVAL_CALL_STAT_INC(name) do { if (_py_stats) _py_stats->call_stats.eval_calls[name]++; } while (0)
+    do { if (_Py_stats && cond) _Py_stats->object_stats.name++; } while (0)
+#define EVAL_CALL_STAT_INC(name) do { if (_Py_stats) _Py_stats->call_stats.eval_calls[name]++; } while (0)
 #define EVAL_CALL_STAT_INC_IF_FUNCTION(name, callable) \
-    do { if (_py_stats && PyFunction_Check(callable)) _py_stats->call_stats.eval_calls[name]++; } while (0)
-#define GC_STAT_ADD(gen, name, n) do { if (_py_stats) _py_stats->gc_stats[(gen)].name += (n); } while (0)
+    do { if (_Py_stats && PyFunction_Check(callable)) _Py_stats->call_stats.eval_calls[name]++; } while (0)
+#define GC_STAT_ADD(gen, name, n) do { if (_Py_stats) _Py_stats->gc_stats[(gen)].name += (n); } while (0)
 
 // Export for '_opcode' shared extension
 PyAPI_FUNC(PyObject*) _Py_GetSpecializationStats(void);
diff --git a/Include/internal/pycore_pystats.h b/Include/internal/pycore_pystats.h
new file mode 100644
index 0000000..f8af398
--- /dev/null
+++ b/Include/internal/pycore_pystats.h
@@ -0,0 +1,21 @@
+#ifndef Py_INTERNAL_PYSTATS_H
+#define Py_INTERNAL_PYSTATS_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef Py_BUILD_CORE
+#  error "this header requires Py_BUILD_CORE define"
+#endif
+
+#ifdef Py_STATS
+extern void _Py_StatsOn(void);
+extern void _Py_StatsOff(void);
+extern void _Py_StatsClear(void);
+extern int _Py_PrintSpecializationStats(int to_file);
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+#endif  // !Py_INTERNAL_PYSTATS_H