Revert "bpo-33929: multiprocessing: fix handle leak on race condition (GH-7921)" (GH-7963)

This reverts commit 8b1ebcd7.

Lib/multiprocessing/popen_spawn_win32.py

@@ -18,12 +18,6 @@ TERMINATE = 0x10000
 WINEXE = (sys.platform == 'win32' and getattr(sys, 'frozen', False))
 WINSERVICE = sys.executable.lower().endswith("pythonservice.exe")
 
-
-def _close_handles(*handles):
-    for handle in handles:
-        _winapi.CloseHandle(handle)
-
-
 #
 # We define a Popen class similar to the one from subprocess, but
 # whose constructor takes a process object as its argument.
@@ -38,12 +32,8 @@ class Popen(object):
     def __init__(self, process_obj):
         prep_data = spawn.get_preparation_data(process_obj._name)
 
-        # read end of pipe will be duplicated by the child process
+        # read end of pipe will be "stolen" by the child process
         # -- see spawn_main() in spawn.py.
-        #
-        # bpo-33929: Previously, the read end of pipe was "stolen" by the child
-        # process, but it leaked a handle if the child process had been
-        # terminated before it could steal the handle from the parent process.
         rhandle, whandle = _winapi.CreatePipe(None, 0)
         wfd = msvcrt.open_osfhandle(whandle, 0)
         cmd = spawn.get_command_line(parent_pid=os.getpid(),
@@ -66,8 +56,7 @@ class Popen(object):
             self.returncode = None
             self._handle = hp
             self.sentinel = int(hp)
-            self.finalizer = util.Finalize(self, _close_handles,
-                                           (self.sentinel, int(rhandle)))
+            self.finalizer = util.Finalize(self, _winapi.CloseHandle, (self.sentinel,))
 
             # send information to child
             set_spawning_popen(self)

Lib/multiprocessing/reduction.py

@@ -68,16 +68,12 @@ if sys.platform == 'win32':
     __all__ += ['DupHandle', 'duplicate', 'steal_handle']
     import _winapi
 
-    def duplicate(handle, target_process=None, inheritable=False,
-                  *, source_process=None):
+    def duplicate(handle, target_process=None, inheritable=False):
         '''Duplicate a handle.  (target_process is a handle not a pid!)'''
-        current_process = _winapi.GetCurrentProcess()
-        if source_process is None:
-            source_process = current_process
         if target_process is None:
-            target_process = current_process
+            target_process = _winapi.GetCurrentProcess()
         return _winapi.DuplicateHandle(
-            source_process, handle, target_process,
+            _winapi.GetCurrentProcess(), handle, target_process,
             0, inheritable, _winapi.DUPLICATE_SAME_ACCESS)
 
     def steal_handle(source_pid, handle):

Lib/multiprocessing/spawn.py

@@ -96,15 +96,7 @@ def spawn_main(pipe_handle, parent_pid=None, tracker_fd=None):
     assert is_forking(sys.argv), "Not forking"
     if sys.platform == 'win32':
         import msvcrt
-        import _winapi
-
-        if parent_pid is not None:
-            source_process = _winapi.OpenProcess(
-                _winapi.PROCESS_DUP_HANDLE, False, parent_pid)
-        else:
-            source_process = None
-        new_handle = reduction.duplicate(pipe_handle,
-                                         source_process=source_process)
+        new_handle = reduction.steal_handle(parent_pid, pipe_handle)
         fd = msvcrt.open_osfhandle(new_handle, os.O_RDONLY)
     else:
         from . import semaphore_tracker

Misc/NEWS.d/next/Library/2018-06-26-02-09-18.bpo-33929.OcCLah.rst

-multiprocessing: Fix a race condition in Popen of
-multiprocessing.popen_spawn_win32. The child process now duplicates the read
-end of pipe instead of "stealing" it. Previously, the read end of pipe was
-"stolen" by the child process, but it leaked a handle if the child process had
-been terminated before it could steal the handle from the parent process.