Python issue #23347: Refactor creation of subprocess transports

Changes on BaseSubprocessTransport:

* Add a wait() method to wait until the child process exit
* The constructor now accepts an optional waiter parameter. The _post_init()
  coroutine must not be called explicitly anymore. It makes subprocess
  transports closer to other transports, and it gives more freedom if we want
  later to change completly how subprocess transports are created.
* close() now kills the process instead of kindly terminate it: the child
  process may ignore SIGTERM and continue to run. Call explicitly terminate()
  and wait() if you want to kindly terminate the child process.
* close() now logs a warning in debug mode if the process is still running and
  needs to be killed
* _make_subprocess_transport() is now fully asynchronous again: if the creation
  of the transport failed, wait asynchronously for the process eixt. Before the
  wait was synchronous. This change requires close() to *kill*, and not
  terminate, the child process.
* Remove the _kill_wait() method, replaced with a more agressive close()
  method. It fixes _make_subprocess_transport() on error.
  BaseSubprocessTransport.close() calls the close() method of pipe transports,
  whereas _kill_wait() closed directly pipes of the subprocess.Popen object
  without unregistering file descriptors from the selector (which caused severe
  bugs).

These changes simplifies the code of subprocess.py.

5 files changed, 92 insertions, 97 deletions

diff --git a/asyncio/base_subprocess.py b/asyncio/base_subprocess.py
index 651a9a2..afeda13 100644
--- a/asyncio/base_subprocess.py
+++ b/asyncio/base_subprocess.py
@@ -3,6 +3,7 @@ import subprocess
 import sys
 import warnings
 
+from . import futures
 from . import protocols
 from . import transports
 from .coroutines import coroutine
@@ -13,27 +14,32 @@ class BaseSubprocessTransport(transports.SubprocessTransport):
 
     def __init__(self, loop, protocol, args, shell,
                  stdin, stdout, stderr, bufsize,
-                 extra=None, **kwargs):
+                 waiter=None, extra=None, **kwargs):
         super().__init__(extra)
         self._closed = False
         self._protocol = protocol
         self._loop = loop
+        self._proc = None
         self._pid = None
-
+        self._returncode = None
+        self._exit_waiters = []
+        self._pending_calls = collections.deque()
         self._pipes = {}
+        self._finished = False
+
         if stdin == subprocess.PIPE:
             self._pipes[0] = None
         if stdout == subprocess.PIPE:
             self._pipes[1] = None
         if stderr == subprocess.PIPE:
             self._pipes[2] = None
-        self._pending_calls = collections.deque()
-        self._finished = False
-        self._returncode = None
+
+        # Create the child process: set the _proc attribute
         self._start(args=args, shell=shell, stdin=stdin, stdout=stdout,
                     stderr=stderr, bufsize=bufsize, **kwargs)
         self._pid = self._proc.pid
         self._extra['subprocess'] = self._proc
+
         if self._loop.get_debug():
             if isinstance(args, (bytes, str)):
                 program = args
@@ -42,6 +48,8 @@ class BaseSubprocessTransport(transports.SubprocessTransport):
             logger.debug('process %r created: pid %s',
                          program, self._pid)
 
+        self._loop.create_task(self._connect_pipes(waiter))
+
     def __repr__(self):
         info = [self.__class__.__name__]
         if self._closed:
@@ -77,12 +85,23 @@ class BaseSubprocessTransport(transports.SubprocessTransport):
 
     def close(self):
         self._closed = True
+
         for proto in self._pipes.values():
             if proto is None:
                 continue
             proto.pipe.close()
-        if self._returncode is None:
-            self.terminate()
+
+        if self._proc is not None and self._returncode is None:
+            if self._loop.get_debug():
+                logger.warning('Close running child process: kill %r', self)
+
+            try:
+                self._proc.kill()
+            except ProcessLookupError:
+                pass
+
+            # Don't clear the _proc reference yet because _post_init() may
+            # still run
 
     # On Python 3.3 and older, objects with a destructor part of a reference
     # cycle are never destroyed. It's not more the case on Python 3.4 thanks
@@ -114,50 +133,24 @@ class BaseSubprocessTransport(transports.SubprocessTransport):
     def kill(self):
         self._proc.kill()
 
-    def _kill_wait(self):
-        """Close pipes, kill the subprocess and read its return status.
-
-        Function called when an exception is raised during the creation
-        of a subprocess.
-        """
-        self._closed = True
-        if self._loop.get_debug():
-            logger.warning('Exception during subprocess creation, '
-                           'kill the subprocess %r',
-                           self,
-                           exc_info=True)
-
-        proc = self._proc
-        if proc.stdout:
-            proc.stdout.close()
-        if proc.stderr:
-            proc.stderr.close()
-        if proc.stdin:
-            proc.stdin.close()
-
-        try:
-            proc.kill()
-        except ProcessLookupError:
-            pass
-        self._returncode = proc.wait()
-
-        self.close()
-
     @coroutine
-    def _post_init(self):
+    def _connect_pipes(self, waiter):
         try:
             proc = self._proc
             loop = self._loop
+
             if proc.stdin is not None:
                 _, pipe = yield from loop.connect_write_pipe(
                     lambda: WriteSubprocessPipeProto(self, 0),
                     proc.stdin)
                 self._pipes[0] = pipe
+
             if proc.stdout is not None:
                 _, pipe = yield from loop.connect_read_pipe(
                     lambda: ReadSubprocessPipeProto(self, 1),
                     proc.stdout)
                 self._pipes[1] = pipe
+
             if proc.stderr is not None:
                 _, pipe = yield from loop.connect_read_pipe(
                     lambda: ReadSubprocessPipeProto(self, 2),
@@ -166,13 +159,16 @@ class BaseSubprocessTransport(transports.SubprocessTransport):
 
             assert self._pending_calls is not None
 
-            self._loop.call_soon(self._protocol.connection_made, self)
+            loop.call_soon(self._protocol.connection_made, self)
             for callback, data in self._pending_calls:
-                self._loop.call_soon(callback, *data)
+                loop.call_soon(callback, *data)
             self._pending_calls = None
-        except:
-            self._kill_wait()
-            raise
+        except Exception as exc:
+            if waiter is not None and not waiter.cancelled():
+                waiter.set_exception(exc)
+        else:
+            if waiter is not None and not waiter.cancelled():
+                waiter.set_result(None)
 
     def _call(self, cb, *data):
         if self._pending_calls is not None:
@@ -197,6 +193,23 @@ class BaseSubprocessTransport(transports.SubprocessTransport):
         self._call(self._protocol.process_exited)
         self._try_finish()
 
+        # wake up futures waiting for wait()
+        for waiter in self._exit_waiters:
+            if not waiter.cancelled():
+                waiter.set_result(returncode)
+        self._exit_waiters = None
+
+    def wait(self):
+        """Wait until the process exit and return the process return code.
+
+        This method is a coroutine."""
+        if self._returncode is not None:
+            return self._returncode
+
+        waiter = futures.Future(loop=self._loop)
+        self._exit_waiters.append(waiter)
+        return (yield from waiter)
+
     def _try_finish(self):
         assert not self._finished
         if self._returncode is None:
@@ -210,9 +223,9 @@ class BaseSubprocessTransport(transports.SubprocessTransport):
         try:
             self._protocol.connection_lost(exc)
         finally:
+            self._loop = None
             self._proc = None
             self._protocol = None
-            self._loop = None
 
 
 class WriteSubprocessPipeProto(protocols.BaseProtocol):
diff --git a/asyncio/subprocess.py b/asyncio/subprocess.py
index c848a21..49b2d7c 100644
--- a/asyncio/subprocess.py
+++ b/asyncio/subprocess.py
@@ -25,8 +25,6 @@ class SubprocessStreamProtocol(streams.FlowControlMixin,
         super().__init__(loop=loop)
         self._limit = limit
         self.stdin = self.stdout = self.stderr = None
-        self.waiter = futures.Future(loop=loop)
-        self._waiters = collections.deque()
         self._transport = None
 
     def __repr__(self):
@@ -61,9 +59,6 @@ class SubprocessStreamProtocol(streams.FlowControlMixin,
                                               reader=None,
                                               loop=self._loop)
 
-        if not self.waiter.cancelled():
-            self.waiter.set_result(None)
-
     def pipe_data_received(self, fd, data):
         if fd == 1:
             reader = self.stdout
@@ -94,16 +89,9 @@ class SubprocessStreamProtocol(streams.FlowControlMixin,
                 reader.set_exception(exc)
 
     def process_exited(self):
-        returncode = self._transport.get_returncode()
         self._transport.close()
         self._transport = None
 
-        # wake up futures waiting for wait()
-        while self._waiters:
-            waiter = self._waiters.popleft()
-            if not waiter.cancelled():
-                waiter.set_result(returncode)
-
 
 class Process:
     def __init__(self, transport, protocol, loop):
@@ -124,15 +112,10 @@ class Process:
 
     @coroutine
     def wait(self):
-        """Wait until the process exit and return the process return code."""
-        returncode = self._transport.get_returncode()
-        if returncode is not None:
-            return returncode
+        """Wait until the process exit and return the process return code.
 
-        waiter = futures.Future(loop=self._loop)
-        self._protocol._waiters.append(waiter)
-        yield from waiter
-        return waiter.result()
+        This method is a coroutine."""
+        return (yield from self._transport.wait())
 
     def _check_alive(self):
         if self._transport.get_returncode() is not None:
@@ -221,11 +204,6 @@ def create_subprocess_shell(cmd, stdin=None, stdout=None, stderr=None,
                                             protocol_factory,
                                             cmd, stdin=stdin, stdout=stdout,
                                             stderr=stderr, **kwds)
-    try:
-        yield from protocol.waiter
-    except:
-        transport._kill_wait()
-        raise
     return Process(transport, protocol, loop)
 
 @coroutine
@@ -241,9 +219,4 @@ def create_subprocess_exec(program, *args, stdin=None, stdout=None,
                                             program, *args,
                                             stdin=stdin, stdout=stdout,
                                             stderr=stderr, **kwds)
-    try:
-        yield from protocol.waiter
-    except:
-        transport._kill_wait()
-        raise
     return Process(transport, protocol, loop)
diff --git a/asyncio/unix_events.py b/asyncio/unix_events.py
index b06f1b2..3ecdfd2 100644
--- a/asyncio/unix_events.py
+++ b/asyncio/unix_events.py
@@ -16,6 +16,7 @@ from . import base_subprocess
 from . import constants
 from . import coroutines
 from . import events
+from . import futures
 from . import selector_events
 from . import selectors
 from . import transports
@@ -175,16 +176,20 @@ class _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
                                    stdin, stdout, stderr, bufsize,
                                    extra=None, **kwargs):
         with events.get_child_watcher() as watcher:
+            waiter = futures.Future(loop=self)
             transp = _UnixSubprocessTransport(self, protocol, args, shell,
                                               stdin, stdout, stderr, bufsize,
-                                              extra=extra, **kwargs)
+                                              waiter=waiter, extra=extra,
+                                              **kwargs)
+
+            watcher.add_child_handler(transp.get_pid(),
+                                      self._child_watcher_callback, transp)
             try:
-                yield from transp._post_init()
+                yield from waiter
             except:
                 transp.close()
+                yield from transp.wait()
                 raise
-            watcher.add_child_handler(transp.get_pid(),
-                                      self._child_watcher_callback, transp)
 
         return transp
 
@@ -774,7 +779,7 @@ class SafeChildWatcher(BaseChildWatcher):
         pass
 
     def add_child_handler(self, pid, callback, *args):
-        self._callbacks[pid] = callback, args
+        self._callbacks[pid] = (callback, args)
 
         # Prevent a race condition in case the child is already terminated.
         self._do_waitpid(pid)
diff --git a/asyncio/windows_events.py b/asyncio/windows_events.py
index 94aafb6..437eb0a 100644
--- a/asyncio/windows_events.py
+++ b/asyncio/windows_events.py
@@ -366,13 +366,16 @@ class ProactorEventLoop(proactor_events.BaseProactorEventLoop):
     def _make_subprocess_transport(self, protocol, args, shell,
                                    stdin, stdout, stderr, bufsize,
                                    extra=None, **kwargs):
+        waiter = futures.Future(loop=self)
         transp = _WindowsSubprocessTransport(self, protocol, args, shell,
                                              stdin, stdout, stderr, bufsize,
-                                             extra=extra, **kwargs)
+                                             waiter=waiter, extra=extra,
+                                             **kwargs)
         try:
-            yield from transp._post_init()
+            yield from waiter
         except:
             transp.close()
+            yield from transp.wait()
             raise
 
         return transp
diff --git a/tests/test_events.py b/tests/test_events.py
index 12af62b..4b957d8 100644
--- a/tests/test_events.py
+++ b/tests/test_events.py
@@ -1551,9 +1551,10 @@ class SubprocessTestsMixin:
         stdin = transp.get_pipe_transport(0)
         stdin.write(b'Python The Winner')
         self.loop.run_until_complete(proto.got_data[1].wait())
-        transp.close()
+        with test_utils.disable_logger():
+            transp.close()
         self.loop.run_until_complete(proto.completed)
-        self.check_terminated(proto.returncode)
+        self.check_killed(proto.returncode)
         self.assertEqual(b'Python The Winner', proto.data[1])
 
     def test_subprocess_interactive(self):
@@ -1567,21 +1568,20 @@ class SubprocessTestsMixin:
         self.loop.run_until_complete(proto.connected)
         self.assertEqual('CONNECTED', proto.state)
 
-        try:
-            stdin = transp.get_pipe_transport(0)
-            stdin.write(b'Python ')
-            self.loop.run_until_complete(proto.got_data[1].wait())
-            proto.got_data[1].clear()
-            self.assertEqual(b'Python ', proto.data[1])
-
-            stdin.write(b'The Winner')
-            self.loop.run_until_complete(proto.got_data[1].wait())
-            self.assertEqual(b'Python The Winner', proto.data[1])
-        finally:
-            transp.close()
+        stdin = transp.get_pipe_transport(0)
+        stdin.write(b'Python ')
+        self.loop.run_until_complete(proto.got_data[1].wait())
+        proto.got_data[1].clear()
+        self.assertEqual(b'Python ', proto.data[1])
 
+        stdin.write(b'The Winner')
+        self.loop.run_until_complete(proto.got_data[1].wait())
+        self.assertEqual(b'Python The Winner', proto.data[1])
+
+        with test_utils.disable_logger():
+            transp.close()
         self.loop.run_until_complete(proto.completed)
-        self.check_terminated(proto.returncode)
+        self.check_killed(proto.returncode)
 
     def test_subprocess_shell(self):
         connect = self.loop.subprocess_shell(
@@ -1739,9 +1739,10 @@ class SubprocessTestsMixin:
             # GetLastError()==ERROR_INVALID_NAME on Windows!?!  (Using
             # WriteFile() we get ERROR_BROKEN_PIPE as expected.)
             self.assertEqual(b'ERR:OSError', proto.data[2])
-        transp.close()
+        with test_utils.disable_logger():
+            transp.close()
         self.loop.run_until_complete(proto.completed)
-        self.check_terminated(proto.returncode)
+        self.check_killed(proto.returncode)
 
     def test_subprocess_wait_no_same_group(self):
         # start the new process in a new session