8000 gh-121313: Limit the reading size from pipes to their default buffer size on Unix systems by aplaikner · Pull Request #121315 · python/cpython · GitHub
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gh-121313: Limit the reading size from pipes to their default buffer size on Unix systems #121315

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21 changes: 18 additions & 3 deletions Lib/multiprocessing/connection.py
Original file line number Diff line number Diff line change
Expand Up @@ -11,13 +11,14 @@

import errno
import io
import itertools
import os
import stat
import sys
import socket
import struct
import time
import tempfile
import itertools
import time


from . import util
Expand Down Expand Up @@ -360,6 +361,11 @@ def _get_more_data(self, ov, maxsize):
f.write(ov.getbuffer())
return f

"""
The default size of a pipe on Linux systems is 16 times the base page size:
https://man7.org/linux/man-pages/man7/pipe.7.html
"""
PAGES_PER_PIPE = 16

class Connection(_ConnectionBase):
"""
Expand All @@ -372,11 +378,14 @@ def _close(self, _close=_multiprocessing.closesocket):
_close(self._handle)
_write = _multiprocessing.send
_read = _multiprocessing.recv
_default_pipe_size = 0
else:
def _close(self, _close=os.close):
_close(self._handle)
_write = os.write
_read = os.read
_base_page_size = os.sysconf(os.sysconf_names['SC_PAGESIZE'])
_default_pipe_size = _base_page_size * PAGES_PER_PIPE

def _send(self, buf, write=_write):
remaining = len(buf)
Expand All @@ -391,8 +400,14 @@ def _recv(self, size, read=_read):
buf = io.BytesIO()
handle = self._handle
remaining = size
is_pipe = False
if size > self._default_pipe_size > 0:
mode = os.fstat(handle).st_mode
is_pipe = stat.S_ISFIFO(mode)
limit = self._default_pipe_size if is_pipe else remaining
while remaining > 0:
chunk = read(handle, remaining)
to_read = min(limit, remaining)
chunk = read(handle, to_read)
n = len(chunk)
if n == 0:
if remaining == size:
Expand Down
Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Limit reading size in multiprocessing connection._recv for pipes to default pipe size of 16 times base page size, in order to avoid memory overallocation and unnecessary memory management system calls.
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