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This is an early C prototype for python/cpython#159207, based on aab474a35b7d47aa3404db0fd5cb2c0314090941. The patch replaces the sample writer and reader. It uses column blocks, exact timestamp residuals, stack reuse, packed flags, and frame byte planes. Shared string and frame tables keep their current representation. The prototype uses format version 2 and reads its own files only.

Both variants use the same Python executable, GCC 15.2 with -O3, and zstd 1.5.7 at level 5. The main comparison uses seven pairs, with the order reversed on each repeat. Each action runs in a fresh process on CPU 2. This was a busy shared Linux host with an AMD Ryzen AI Max+ 395. Treat small timing differences as inconclusive.

Write time covers writer creation, prepared samples, and finalization. Replay time covers reader creation, replay to a counter, and reader close. These measurements exclude remote stack capture and report export. File sizes include all metadata. Peak RSS includes Python and the shared tables. Files use

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-> Running: ./a.sh
-> Attaching to process 22778...
-> [startup pid=22778] waiting for initial TRACEME stop
-> [startup pid=22778] initial trace stop observed with signal SIGTRAP
-> [startup pid=22778] startup ptrace guard attached
-> [startup pid=22778] startup probe loop begins
-> [startup pid=22778] acquiring task port (context=runtime-detection)
-> [startup pid=22778] runtime-detection skipped (no task port)
-> [startup pid=22778] python_image_active=false
-> [startup pid=22778] ptrace::cont(signal=None)

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file,import_line,import_api,variable,attr_access_api,attr_access_line,import_code,attr_access_code
Modules/_asynciomodule.c,4264,PyImport_ImportModule,asyncio_mod,NONE DETECTED,,"state->asyncio_mod = PyImport_ImportModule(""asyncio"");",
Modules/_asynciomodule.c,4281,PyImport_ImportModule,module,PyObject_GetAttrString,4287,module = PyImport_ImportModule(NAME); \,"VAR = PyObject_GetAttrString(module, NAME); \"
Modules/_ctypes/callbacks.c,474,PyImport_ImportModuleAttrString,func,NONE DETECTED,,"func = PyImport_ImportModuleAttrString(""ctypes"", ""DllGetClassObject"");",
Modules/_ctypes/callbacks.c,543,PyImport_ImportModuleAttrString,func,NONE DETECTED,,"PyObject *func = PyImport_ImportModuleAttrString(""ctypes"",",
Modules/_ctypes/stgdict.c,272,PyImport_ImportModuleAttrString,layout_func,NONE DETECTED,,"layout_func = PyImport_ImportModuleAttrString(""ctypes._layout"", ""get_layout"");",
Modules/_cursesmodule.c,328,PyImport_ImportModuleAttrString,exc,NONE DETECTED,,"PyObject *exc = PyImport_ImportModuleAttrStrin

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how do you feel about these stacks?
Traceback for thread 2896 (python) [Garbage collecting] (most recent call last):
    (C) File "???", line 0, in _start (/home/mwoznisk/3ps/cpython/python)
    (C) File "../csu/libc-start.c", line 302, in __libc_start_main (/usr/lib64/libc-2.28.so)
    (C) File "Modules/main.c", line 829, in Py_BytesMain (/home/mwoznisk/3ps/cpython/python)
    (C) File "Modules/main.c", line 805, in pymain_main (inlined) (/home/mwoznisk/3ps/cpython/python)
    (C) File "Modules/main.c", line 777, in Py_RunMain (inlined) (/home/mwoznisk/3ps/cpython/python)
    (C) File "Python/gc_free_threading.c", line 2608, in PyGC_Collect (/home/mwoznisk/3ps/cpython/python)
    (C) File "Python/gc_free_threading.c", line 2314, in gc_collect_main.constprop.0 (/home/mwoznisk/3ps/cpython/python)
    (C) File "Python/gc_free_threading.c", line 2144, in gc_collect_internal (inlined) (/home/mwoznisk/3ps/cpython/python)

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#1  _PyCode_GetTLBCArray (co=0x0) at ./Include/internal/pycore_code.h:529
529         return _Py_STATIC_CAST(_PyCodeArray *,
(gdb) up
#2  _PyFrame_GetBytecode (f=0x727f2e2331a8) at ./Include/internal/pycore_interpframe.h:32
32          _PyCodeArray *tlbc = _PyCode_GetTLBCArray(co);
(gdb) up
#3  PyUnstable_InterpreterFrame_GetLine (frame=0x727f2e2331a8) at Python/frame.c:149
149         int addr = _PyInterpreterFrame_LASTI(frame) * sizeof(_Py_CODEUNIT);
(gdb) p *frame
$1 = {f_executable = 0x0, previous = 0x727f2e233128, f_funcobj = 0x0,

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#1  _PyCode_GetTLBCArray (co=0x0) at ./Include/internal/pycore_code.h:529
529         return _Py_STATIC_CAST(_PyCodeArray *,
(gdb) up
#2  _PyFrame_GetBytecode (f=0x727f2e2331a8) at ./Include/internal/pycore_interpframe.h:32
32          _PyCodeArray *tlbc = _PyCode_GetTLBCArray(co);
(gdb) up
#3  PyUnstable_InterpreterFrame_GetLine (frame=0x727f2e2331a8) at Python/frame.c:149
149         int addr = _PyInterpreterFrame_LASTI(frame) * sizeof(_Py_CODEUNIT);
(gdb) p *frame
$1 = {f_executable = 0x0, previous = 0x727f2e233128, f_funcobj = 0x0,

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import sys
import threading
import time

from memray._test import MemoryAllocator


def background_attacher():
    time.sleep(1)
    import memray

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import argparse
import _remote_debugging
import time
import signal
from collections import defaultdict

class SamplingProfiler:
    def __init__(self):
        self.function_stats = defaultdict(lambda: {'ncalls': 0, 'tottime': 0.0})
        self.total_samples = 0

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import tokenize
from io import BytesIO
from typing import List, Tuple, Optional, Dict, Any
import keyword
from codeop import compile_command
from _suggestions import _generate_suggestions
from textwrap import dedent

class StatementFinder:
    """Finds the smallest surrounding statement given a line number and Python source."""