gh-150107: Fix asyncio sendfile fallback ignoring non-zero offset

The fallback paths in BaseEventLoop._sock_sendfile_fallback and
_sendfile_fallback only seeked the file when offset was truthy, so an
offset of 0 was respected but later non-zero offsets were dropped when
the file lacked seek tracking. Seek whenever the file supports seek().
Also seek the CRT file pointer on Windows TransmitFile, which ignores
OVERLAPPED.Offset for handles not opened with FILE_FLAG_OVERLAPPED.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: 2 people

Lib/asyncio/base_events.py

@@ -969,7 +969,7 @@ async def _sock_sendfile_native(self, sock, file, offset, count):
             f"and file {file!r} combination")
 
     async def _sock_sendfile_fallback(self, sock, file, offset, count):
-        if offset:
+        if hasattr(file, 'seek'):
             file.seek(offset)
         blocksize = (
             min(count, constants.SENDFILE_FALLBACK_READBUFFER_SIZE)
@@ -1286,7 +1286,6 @@ async def sendfile(self, transport, file, offset=0, count=None,
             raise RuntimeError(
                 f"fallback is disabled and native sendfile is not "
                 f"supported for transport {transport!r}")
-
         return await self._sendfile_fallback(transport, file,
                                              offset, count)
 
@@ -1295,7 +1294,7 @@ async def _sendfile_native(self, transp, file, offset, count):
             "sendfile syscall is not supported")
 
     async def _sendfile_fallback(self, transp, file, offset, count):
-        if offset:
+        if hasattr(file, 'seek'):
             file.seek(offset)
         blocksize = min(count, 16384) if count else 16384
         buf = bytearray(blocksize)

Lib/asyncio/windows_events.py

@@ -610,6 +610,9 @@ def sendfile(self, sock, file, offset, count):
         ov = _overlapped.Overlapped(NULL)
         offset_low = offset & 0xffff_ffff
         offset_high = (offset >> 32) & 0xffff_ffff
+        # TransmitFile ignores OVERLAPPED.Offset for handles not opened with
+        # FILE_FLAG_OVERLAPPED, so seek the CRT file pointer to match.
+        file.seek(offset)
         ov.TransmitFile(sock.fileno(),
                         msvcrt.get_osfhandle(file.fileno()),
                         offset_low, offset_high,

Lib/test/libregrtest/logger.py

@@ -1,5 +1,6 @@
 import os
 import time
+from typing import Callable
 
 from test.support import MS_WINDOWS
 from .results import TestResults
@@ -19,16 +20,27 @@ def __init__(self, results: TestResults, quiet: bool, pgo: bool):
         self._results: TestResults = results
         self._quiet: bool = quiet
         self._pgo: bool = pgo
+        self.get_mem_usage: Callable[[], int | None] | None = None
 
     def log(self, line: str = '') -> None:
         empty = not line
 
-        # add the system load prefix: "load avg: 1.80 "
+        # Add the memory usage: "mem: 1 GiB "
+        if self.get_mem_usage is not None:
+            mem = self.get_mem_usage()
+            if mem:
+                mib = mem / (1024*1024)
+                if mib >= 1024:
+                    line = f"mem: {mib / 1024:.1f} GiB {line}"
+                else:
+                    line = f"mem: {mib:.1f} MiB {line}"
+
+        # Add the system load prefix: "load avg: 1.80 "
         load_avg = self.get_load_avg()
         if load_avg is not None:
             line = f"load avg: {load_avg:.2f} {line}"
 
-        # add the timestamp prefix:  "0:01:05 "
+        # Add the timestamp prefix:  "0:01:05 "
         log_time = time.perf_counter() - self.start_time
 
         mins, secs = divmod(int(log_time), 60)

Lib/test/libregrtest/run_workers.py

@@ -22,7 +22,7 @@
 from .single import PROGRESS_MIN_TIME
 from .utils import (
     StrPath, TestName,
-    format_duration, print_warning, count, plural)
+    format_duration, print_warning, count, plural, get_process_memory_usage)
 from .worker import create_worker_process, USE_PROCESS_GROUP
 
 if MS_WINDOWS:
@@ -452,6 +452,12 @@ def wait_stopped(self, start_time: float) -> None:
                 print_warning(f"Failed to join {self} in {format_duration(dt)}")
                 break
 
+    def get_mem_usage(self):
+        popen = self._popen
+        if popen is None:
+            return
+        return get_process_memory_usage(popen.pid)
+
 
 def get_running(workers: list[WorkerThread]) -> str | None:
     running: list[str] = []
@@ -473,6 +479,7 @@ def __init__(self, num_workers: int, runtests: RunTests,
                  logger: Logger, results: TestResults) -> None:
         self.num_workers = num_workers
         self.runtests = runtests
+        self.logger = logger
         self.log = logger.log
         self.display_progress = logger.display_progress
         self.results: TestResults = results
@@ -598,9 +605,21 @@ def _process_result(self, item: QueueOutput) -> TestResult:
 
         return result
 
+    def get_mem_usage(self):
+        usage = 0
+        main_mem = get_process_memory_usage(os.getpid())
+        if main_mem:
+            usage += main_mem
+        for worker in self.workers:
+            worker_mem = worker.get_mem_usage()
+            if worker_mem:
+                usage += worker_mem
+        return usage
+
     def run(self) -> None:
         fail_fast = self.runtests.fail_fast
         fail_env_changed = self.runtests.fail_env_changed
+        self.logger.get_mem_usage = self.get_mem_usage
 
         self.start_workers()
 
@@ -625,3 +644,4 @@ def run(self) -> None:
             # worker when we exit this function
             self.pending.stop()
             self.stop_workers()
+            self.logger.get_mem_usage = None

Lib/test/libregrtest/utils.py

@@ -752,3 +752,26 @@ def display_title(title):
     print(title)
     print("#" * len(title))
     print(flush=True)
+
+
+def get_process_memory_usage(pid: int) -> int | None:
+    """
+    Read the private memory in bytes from /proc/pid/smaps.
+    """
+    try:
+        fp = open(f"/proc/{pid}/smaps", "rb")
+    except OSError:
+        return None
+
+    try:
+        total = 0
+        with fp:
+            for line in fp:
+                # Include both Private_Clean and Private_Dirty sections.
+                line = line.rstrip()
+                if line.startswith(b"Private_") and line.endswith(b'kB'):
+                    parts = line.split()
+                    total += int(parts[1]) * 1024
+        return total
+    except ProcessLookupError:
+        return None

Lib/test/test_asyncio/test_sendfile.py

@@ -228,6 +228,32 @@ def test_sock_sendfile_zero_size(self):
         self.assertEqual(ret, 0)
         self.assertEqual(self.file.tell(), 0)
 
+    def check_sock_sendfile_offset(self, data, offset, force_fallback=False):
+        sock, proto = self.prepare_socksendfile()
+        with tempfile.TemporaryFile() as f:
+            f.write(data)
+            f.flush()
+            self.assertEqual(f.tell(), len(data))
+
+            if force_fallback:
+                async def _sock_sendfile_fail(sock, file, offset, count):
+                    raise asyncio.exceptions.SendfileNotAvailableError()
+                with support.swap_attr(self.loop, '_sock_sendfile_native', _sock_sendfile_fail):
+                    ret = self.run_loop(self.loop.sock_sendfile(sock, f, offset, None))
+            else:
+                ret = self.run_loop(self.loop.sock_sendfile(sock, f, offset, None))
+            self.assertEqual(f.tell(), len(data))
+            sock.close()
+            self.run_loop(proto.wait_closed())
+            self.assertEqual(ret, len(data) - offset)
+
+    def test_sock_sendfile_offset(self):
+        data = b'abcdef'
+        for offset in (0, len(data) // 2, len(data)):
+            for force_fallback in (False, True):
+                with self.subTest(offset=offset, force_fallback=force_fallback):
+                    self.check_sock_sendfile_offset(data, offset, force_fallback)
+
     def test_sock_sendfile_mix_with_regular_send(self):
         buf = b"mix_regular_send" * (4 * 1024)  # 64 KiB
         sock, proto = self.prepare_socksendfile()

Lib/test/test_regrtest.py

@@ -41,7 +41,11 @@
 
 ROOT_DIR = os.path.join(os.path.dirname(__file__), '..', '..')
 ROOT_DIR = os.path.abspath(os.path.normpath(ROOT_DIR))
-LOG_PREFIX = r'[0-9]+:[0-9]+:[0-9]+ (?:load avg: [0-9]+\.[0-9]{2} )?'
+LOG_PREFIX = (
+    r'[0-9]+:[0-9]+:[0-9]+ '
+    r'(?:load avg: [0-9]+\.[0-9]{2} )?'
+    r'(?:mem: [0-9]+\.[0-9] (?:MiB|GiB) )?'
+)
 RESULT_REGEX = (
     'passed',
     'failed',

Misc/NEWS.d/next/Core_and_Builtins/2026-05-22-17-09-28.gh-issue-150107.GD72-D.rst

@@ -0,0 +1,3 @@
+:mod:`asyncio`: ``sendfile()`` and ``sock_sendfile()`` event loop methods
+now call ``file.seek(offset)`` if *file* has a ``seek()`` method,
+even if *offset* is ``0`` (default value).

Misc/NEWS.d/next/Tests/2026-05-22-16-41-45.gh-issue-150114.UdMikH.rst

@@ -0,0 +1,2 @@
+On Linux, regrtest now logs the total memory usage of all Python processes.
+Read the private memory in ``/proc/pid/smaps``. Patch by Victor Stinner.