GH-114695: Add sys._clear_internal_caches (GH-115152)

Author: brandtbucher

Doc/library/sys.rst

@@ -195,6 +195,17 @@ always available.
 
    This function should be used for internal and specialized purposes only.
 
+   .. deprecated:: 3.13
+      Use the more general :func:`_clear_internal_caches` function instead.
+
+
+.. function:: _clear_internal_caches()
+
+   Clear all internal performance-related caches. Use this function *only* to
+   release unnecessary references and memory blocks when hunting for leaks.
+
+   .. versionadded:: 3.13
+
 
 .. function:: _current_frames()
 
@@ -724,7 +735,7 @@ always available.
    regardless of their size.  This function is mainly useful for tracking
    and debugging memory leaks.  Because of the interpreter's internal
    caches, the result can vary from call to call; you may have to call
-   :func:`_clear_type_cache()` and :func:`gc.collect()` to get more
+   :func:`_clear_internal_caches()` and :func:`gc.collect()` to get more
    predictable results.
 
    If a Python build or implementation cannot reasonably compute this

Include/cpython/optimizer.h

@@ -24,9 +24,10 @@ typedef struct {
     uint8_t opcode;
     uint8_t oparg;
     uint8_t valid;
-    uint8_t linked;
+    int index;           // Index of ENTER_EXECUTOR (if code isn't NULL, below).
     _PyBloomFilter bloom;
     _PyExecutorLinkListNode links;
+    PyCodeObject *code;  // Weak (NULL if no corresponding ENTER_EXECUTOR).
 } _PyVMData;
 
 typedef struct {

Lib/test/libregrtest/refleak.py

@@ -201,8 +201,8 @@ def dash_R_cleanup(fs, ps, pic, zdc, abcs):
     # Clear caches
     clear_caches()
 
-    # Clear type cache at the end: previous function calls can modify types
-    sys._clear_type_cache()
+    # Clear other caches last (previous function calls can re-populate them):
+    sys._clear_internal_caches()
 
 
 def warm_caches():

Lib/test/test_capi/test_opt.py

@@ -1,5 +1,6 @@
 import contextlib
 import opcode
+import sys
 import textwrap
 import unittest
 
@@ -181,6 +182,21 @@ def f():
         _testinternalcapi.invalidate_executors(f.__code__)
         self.assertFalse(exe.is_valid())
 
+    def test_sys__clear_internal_caches(self):
+        def f():
+            for _ in range(1000):
+                pass
+        opt = _testinternalcapi.get_uop_optimizer()
+        with temporary_optimizer(opt):
+            f()
+        exe = get_first_executor(f)
+        self.assertIsNotNone(exe)
+        self.assertTrue(exe.is_valid())
+        sys._clear_internal_caches()
+        self.assertFalse(exe.is_valid())
+        exe = get_first_executor(f)
+        self.assertIsNone(exe)
+
 class TestUops(unittest.TestCase):
 
     def test_basic_loop(self):

Lib/test/test_mailbox.py

@@ -10,6 +10,7 @@
 import tempfile
 from test import support
 from test.support import os_helper
+from test.support import refleak_helper
 from test.support import socket_helper
 import unittest
 import textwrap
@@ -2443,6 +2444,9 @@ def test__all__(self):
 
 def tearDownModule():
     support.reap_children()
+    # reap_children may have re-populated caches:
+    if refleak_helper.hunting_for_refleaks():
+        sys._clear_internal_caches()
 
 
 if __name__ == '__main__':

Misc/NEWS.d/next/Core and Builtins/2024-02-07-18-04-36.gh-issue-114695.o9wP5P.rst

@@ -0,0 +1,3 @@
+Add :func:`sys._clear_internal_caches`, which clears all internal
+performance-related caches (and deprecate the less-general
+:func:`sys._clear_type_cache` function).

Objects/codeobject.c

@@ -1489,27 +1489,19 @@ PyCode_GetFreevars(PyCodeObject *code)
 static void
 clear_executors(PyCodeObject *co)
 {
+    assert(co->co_executors);
     for (int i = 0; i < co->co_executors->size; i++) {
-        Py_CLEAR(co->co_executors->executors[i]);
+        if (co->co_executors->executors[i]) {
+            _Py_ExecutorClear(co->co_executors->executors[i]);
+        }
     }
     PyMem_Free(co->co_executors);
     co->co_executors = NULL;
 }
 
 void
-_PyCode_Clear_Executors(PyCodeObject *code) {
-    int code_len = (int)Py_SIZE(code);
-    for (int i = 0; i < code_len; i += _PyInstruction_GetLength(code, i)) {
-        _Py_CODEUNIT *instr = &_PyCode_CODE(code)[i];
-        uint8_t opcode = instr->op.code;
-        uint8_t oparg = instr->op.arg;
-        if (opcode == ENTER_EXECUTOR) {
-            _PyExecutorObject *exec = code->co_executors->executors[oparg];
-            assert(exec->vm_data.opcode != ENTER_EXECUTOR);
-            instr->op.code = exec->vm_data.opcode;
-            instr->op.arg = exec->vm_data.oparg;
-        }
-    }
+_PyCode_Clear_Executors(PyCodeObject *code)
+{
     clear_executors(code);
 }
 
@@ -2360,10 +2352,10 @@ _PyCode_ConstantKey(PyObject *op)
 void
 _PyStaticCode_Fini(PyCodeObject *co)
 {
-    deopt_code(co, _PyCode_CODE(co));
     if (co->co_executors != NULL) {
         clear_executors(co);
     }
+    deopt_code(co, _PyCode_CODE(co));
     PyMem_Free(co->co_extra);
     if (co->_co_cached != NULL) {
         Py_CLEAR(co->_co_cached->_co_code);

Python/bytecodes.c

@@ -2370,23 +2370,12 @@ dummy_func(
             CHECK_EVAL_BREAKER();
 
             PyCodeObject *code = _PyFrame_GetCode(frame);
-            _PyExecutorObject *executor = code->co_executors->executors[oparg & 255];
-            if (executor->vm_data.valid) {
-                Py_INCREF(executor);
-                current_executor = executor;
-                GOTO_TIER_TWO();
-            }
-            else {
-                /* ENTER_EXECUTOR will be the first code unit of the instruction */
-                assert(oparg < 256);
-                code->co_executors->executors[oparg] = NULL;
-                opcode = this_instr->op.code = executor->vm_data.opcode;
-                this_instr->op.arg = executor->vm_data.oparg;
-                oparg = executor->vm_data.oparg;
-                Py_DECREF(executor);
-                next_instr = this_instr;
-                DISPATCH_GOTO();
-            }
+            current_executor = code->co_executors->executors[oparg & 255];
+            assert(current_executor->vm_data.index == INSTR_OFFSET() - 1);
+            assert(current_executor->vm_data.code == code);
+            assert(current_executor->vm_data.valid);
+            Py_INCREF(current_executor);
+            GOTO_TIER_TWO();
         }
 
         replaced op(_POP_JUMP_IF_FALSE, (cond -- )) {

Python/clinic/sysmodule.c.h

@@ -73,25 +73,21 @@ insert_executor(PyCodeObject *code, _Py_CODEUNIT *instr, int index, _PyExecutorO
     Py_INCREF(executor);
     if (instr->op.code == ENTER_EXECUTOR) {
         assert(index == instr->op.arg);
-        _PyExecutorObject *old = code->co_executors->executors[index];
-        executor->vm_data.opcode = old->vm_data.opcode;
-        executor->vm_data.oparg = old->vm_data.oparg;
-        old->vm_data.opcode = 0;
-        code->co_executors->executors[index] = executor;
-        Py_DECREF(old);
+        _Py_ExecutorClear(code->co_executors->executors[index]);
     }
     else {
         assert(code->co_executors->size == index);
         assert(code->co_executors->capacity > index);
-        executor->vm_data.opcode = instr->op.code;
-        executor->vm_data.oparg = instr->op.arg;
-        code->co_executors->executors[index] = executor;
-        assert(index < MAX_EXECUTORS_SIZE);
-        instr->op.code = ENTER_EXECUTOR;
-        instr->op.arg = index;
         code->co_executors->size++;
     }
-    return;
+    executor->vm_data.opcode = instr->op.code;
+    executor->vm_data.oparg = instr->op.arg;
+    executor->vm_data.code = code;
+    executor->vm_data.index = (int)(instr - _PyCode_CODE(code));
+    code->co_executors->executors[index] = executor;
+    assert(index < MAX_EXECUTORS_SIZE);
+    instr->op.code = ENTER_EXECUTOR;
+    instr->op.arg = index;
 }
 
 int
@@ -1071,15 +1067,15 @@ link_executor(_PyExecutorObject *executor)
         }
         head->vm_data.links.next = executor;
     }
-    executor->vm_data.linked = true;
+    executor->vm_data.valid = true;
     /* executor_list_head must be first in list */
     assert(interp->executor_list_head->vm_data.links.previous == NULL);
 }
 
 static void
 unlink_executor(_PyExecutorObject *executor)
 {
-    if (!executor->vm_data.linked) {
+    if (!executor->vm_data.valid) {
         return;
     }
     _PyExecutorLinkListNode *links = &executor->vm_data.links;
@@ -1097,7 +1093,7 @@ unlink_executor(_PyExecutorObject *executor)
         assert(interp->executor_list_head == executor);
         interp->executor_list_head = next;
     }
-    executor->vm_data.linked = false;
+    executor->vm_data.valid = false;
 }
 
 /* This must be called by optimizers before using the executor */
@@ -1116,12 +1112,24 @@ void
 _Py_ExecutorClear(_PyExecutorObject *executor)
 {
     unlink_executor(executor);
+    PyCodeObject *code = executor->vm_data.code;
+    if (code == NULL) {
+        return;
+    }
+    _Py_CODEUNIT *instruction = &_PyCode_CODE(code)[executor->vm_data.index];
+    assert(instruction->op.code == ENTER_EXECUTOR);
+    int index = instruction->op.arg;
+    assert(code->co_executors->executors[index] == executor);
+    instruction->op.code = executor->vm_data.opcode;
+    instruction->op.arg = executor->vm_data.oparg;
+    executor->vm_data.code = NULL;
+    Py_CLEAR(code->co_executors->executors[index]);
 }
 
 void
 _Py_Executor_DependsOn(_PyExecutorObject *executor, void *obj)
 {
-    assert(executor->vm_data.valid = true);
+    assert(executor->vm_data.valid);
     _Py_BloomFilter_Add(&executor->vm_data.bloom, obj);
 }
 
@@ -1140,8 +1148,7 @@ _Py_Executors_InvalidateDependency(PyInterpreterState *interp, void *obj)
         assert(exec->vm_data.valid);
         _PyExecutorObject *next = exec->vm_data.links.next;
         if (bloom_filter_may_contain(&exec->vm_data.bloom, &obj_filter)) {
-            exec->vm_data.valid = false;
-            unlink_executor(exec);
+            _Py_ExecutorClear(exec);
         }
         exec = next;
     }
@@ -1151,15 +1158,14 @@ _Py_Executors_InvalidateDependency(PyInterpreterState *interp, void *obj)
 void
 _Py_Executors_InvalidateAll(PyInterpreterState *interp)
 {
-    /* Walk the list of executors */
-    for (_PyExecutorObject *exec = interp->executor_list_head; exec != NULL;) {
-        assert(exec->vm_data.valid);
-        _PyExecutorObject *next = exec->vm_data.links.next;
-        exec->vm_data.links.next = NULL;
-        exec->vm_data.links.previous = NULL;
-        exec->vm_data.valid = false;
-        exec->vm_data.linked = false;
-        exec = next;
+    while (interp->executor_list_head) {
+        _PyExecutorObject *executor = interp->executor_list_head;
+        if (executor->vm_data.code) {
+            // Clear the entire code object so its co_executors array be freed:
+            _PyCode_Clear_Executors(executor->vm_data.code);
+        }
+        else {
+            _Py_ExecutorClear(executor);
+        }
     }
-    interp->executor_list_head = NULL;
 }

Python/generated_cases.c.h

@@ -2127,6 +2127,22 @@ sys__clear_type_cache_impl(PyObject *module)
     Py_RETURN_NONE;
 }
 
+/*[clinic input]
+sys._clear_internal_caches
+
+Clear all internal performance-related caches.
+[clinic start generated code]*/
+
+static PyObject *
+sys__clear_internal_caches_impl(PyObject *module)
+/*[clinic end generated code: output=0ee128670a4966d6 input=253e741ca744f6e8]*/
+{
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    _Py_Executors_InvalidateAll(interp);
+    PyType_ClearCache();
+    Py_RETURN_NONE;
+}
+
 /* Note that, for now, we do not have a per-interpreter equivalent
   for sys.is_finalizing(). */
 
@@ -2461,6 +2477,7 @@ static PyMethodDef sys_methods[] = {
     {"audit", _PyCFunction_CAST(sys_audit), METH_FASTCALL, audit_doc },
     {"breakpointhook", _PyCFunction_CAST(sys_breakpointhook),
      METH_FASTCALL | METH_KEYWORDS, breakpointhook_doc},
+    SYS__CLEAR_INTERNAL_CACHES_METHODDEF
     SYS__CLEAR_TYPE_CACHE_METHODDEF
     SYS__CURRENT_FRAMES_METHODDEF
     SYS__CURRENT_EXCEPTIONS_METHODDEF