Add workaround for send_handle bug on Windows

See python/cpython#82369

Author: marcelm

src/cutadapt/_handles.py

@@ -0,0 +1,78 @@
+"""
+Wrappers around multiprocessing.reduction.send_handle/recv_handle
+that
+- fix a bug in CPython’s standard library preventing send_handle from
+working on Windows
+- and translate between Windows handles and Unix file descriptors as necessary.
+"""
+
+import multiprocessing
+import os
+
+try:
+    import msvcrt
+except ImportError:
+    msvcrt = None
+try:
+    import _winapi
+except ImportError:
+    _winapi = None
+
+
+class _PatchedDupHandle:
+    """Used by _patched_send_handle"""
+
+    def __init__(self, handle, access, pid=None, options=0):
+        if pid is None:
+            pid = os.getpid()
+        proc = _winapi.OpenProcess(_winapi.PROCESS_DUP_HANDLE, False, pid)
+        try:
+            self._handle = _winapi.DuplicateHandle(
+                _winapi.GetCurrentProcess(), handle, proc, access, False, options
+            )
+        finally:
+            _winapi.CloseHandle(proc)
+        self._access = access
+        self._pid = pid
+
+    def detach(self):
+        if self._pid == os.getpid():
+            return self._handle
+        proc = _winapi.OpenProcess(_winapi.PROCESS_DUP_HANDLE, False, self._pid)
+        try:
+            return _winapi.DuplicateHandle(
+                proc,
+                self._handle,
+                _winapi.GetCurrentProcess(),
+                self._access,
+                False,
+                _winapi.DUPLICATE_CLOSE_SOURCE,
+            )
+        finally:
+            _winapi.CloseHandle(proc)
+
+
+def _patched_send_handle(conn, handle, destination_pid):
+    """
+    A patched version of multiprocessing.reduction.send_handle that works around
+    bug https://github.com/python/cpython/issues/82369
+    Adapted from code posted by Cameron Kennedy (m3rc1fulcameron) in that issue.
+    """
+    dh = _PatchedDupHandle(handle, 0, destination_pid, _winapi.DUPLICATE_SAME_ACCESS)
+    conn.send(dh)
+
+
+def send_handle(conn, fd, destination_pid):
+    if _winapi is None:
+        return multiprocessing.reduction.send_handle(conn, fd, destination_pid)
+    else:
+        handle = msvcrt.get_osfhandle(fd)
+        return _patched_send_handle(conn, handle, destination_pid)
+
+
+def recv_handle(conn):
+    handle = multiprocessing.reduction.recv_handle(conn)
+    if msvcrt:
+        return msvcrt.open_osfhandle(handle, os.O_RDONLY | os.O_BINARY)
+    else:
+        return handle

src/cutadapt/runners.py

@@ -11,6 +11,7 @@
 
 import dnaio
 
+from ._handles import recv_handle, send_handle
 from cutadapt.files import (
     InputFiles,
     OutputFiles,
@@ -85,8 +86,7 @@ def run(self):
             with ExitStack() as stack:
                 try:
                     fds = [
-                        multiprocessing.reduction.recv_handle(self._input_fds_pipe)
-                        for _ in range(self._n_files)
+                        recv_handle(self._input_fds_pipe) for _ in range(self._n_files)
                     ]
                     self._input_fds_pipe.close()
                     raw_files = [
@@ -326,9 +326,7 @@ def __init__(
                 )
             else:
                 with open(path, "rb") as f:
-                    multiprocessing.reduction.send_handle(
-                        input_fds_pipe_w, f.fileno(), pid
-                    )
+                    send_handle(input_fds_pipe_w, f.fileno(), pid)
         input_fds_pipe_w.close()
 
         file_format: Optional[FileFormat] = self._try_receive(file_format_connection_r)