bpo-30805: Avoid race condition with debug logging (GH-7545)

Supersedes https://github.com/python/cpython/pull/2490
(cherry picked from commit 12f482e0ae)

Co-authored-by: Yury Selivanov <yury@magic.io>

Lib/asyncio/base_events.py

@@ -1476,6 +1476,7 @@ class BaseEventLoop(events.AbstractEventLoop):
         if bufsize != 0:
             raise ValueError("bufsize must be 0")
         protocol = protocol_factory()
+        debug_log = None
         if self._debug:
             # don't log parameters: they may contain sensitive information
             # (password) and may be too long
@@ -1483,7 +1484,7 @@ class BaseEventLoop(events.AbstractEventLoop):
             self._log_subprocess(debug_log, stdin, stdout, stderr)
         transport = await self._make_subprocess_transport(
             protocol, cmd, True, stdin, stdout, stderr, bufsize, **kwargs)
-        if self._debug:
+        if self._debug and debug_log is not None:
             logger.info('%s: %r', debug_log, transport)
         return transport, protocol
 
@@ -1504,6 +1505,7 @@ class BaseEventLoop(events.AbstractEventLoop):
                     f"program arguments must be a bytes or text string, "
                     f"not {type(arg).__name__}")
         protocol = protocol_factory()
+        debug_log = None
         if self._debug:
             # don't log parameters: they may contain sensitive information
             # (password) and may be too long
@@ -1512,7 +1514,7 @@ class BaseEventLoop(events.AbstractEventLoop):
         transport = await self._make_subprocess_transport(
             protocol, popen_args, False, stdin, stdout, stderr,
             bufsize, **kwargs)
-        if self._debug:
+        if self._debug and debug_log is not None:
             logger.info('%s: %r', debug_log, transport)
         return transport, protocol
 

Misc/NEWS.d/next/Library/2018-06-08-17-34-16.bpo-30805.3qCWa0.rst

@@ -0,0 +1 @@
+Avoid race condition with debug logging