[downloader/external] Fix "Resource Warning" in downloader test

* add compat_subprocess_Popen context manager
* apply context manager in FFmpegFD._call_downloader()

youtube_dl/compat.py

@@ -2438,9 +2438,9 @@ compat_html_parser_HTMLParser = compat_HTMLParser
 compat_html_parser_HTMLParseError = compat_HTMLParseError
 
 try:
-    from subprocess import DEVNULL
+    _DEVNULL = subprocess.DEVNULL
-    compat_subprocess_get_DEVNULL = lambda: DEVNULL
+    compat_subprocess_get_DEVNULL = lambda: _DEVNULL
-except ImportError:
+except AttributeError:
     compat_subprocess_get_DEVNULL = lambda: open(os.path.devnull, 'w')
 
 try:
@@ -2958,6 +2958,33 @@ except ImportError:
             return exc_val is not None and isinstance(exc_val, self._exceptions or tuple())
 
 
+# subprocess.Popen context manager
+# avoids leaking handles if .communicate() is not called
+try:
+    _Popen = subprocess.Popen
+    # check for required context manager attributes
+    _Popen.__enter__ and _Popen.__exit__
+    compat_subprocess_Popen = _Popen
+except AttributeError:
+    # not a context manager - make one
+    from contextlib import contextmanager
+
+    @contextmanager
+    def compat_subprocess_Popen(*args, **kwargs):
+        popen = None
+        try:
+            popen = _Popen(*args, **kwargs)
+            yield popen
+        finally:
+            if popen:
+                for f in (popen.stdin, popen.stdout, popen.stderr):
+                    if f:
+                        # repeated .close() is OK, but just in case
+                        with compat_contextlib_suppress(EnvironmentError):
+                            f.close()
+                popen.wait()
+
+
 # Fix https://github.com/ytdl-org/youtube-dl/issues/4223
 # See http://bugs.python.org/issue9161 for what is broken
 def workaround_optparse_bug9161():
@@ -3314,6 +3341,7 @@ __all__ = [
     'compat_struct_pack',
     'compat_struct_unpack',
     'compat_subprocess_get_DEVNULL',
+    'compat_subprocess_Popen',
     'compat_tokenize_tokenize',
     'compat_urllib_error',
     'compat_urllib_parse',

youtube_dl/downloader/external.py

@@ -11,6 +11,7 @@ from .common import FileDownloader
 from ..compat import (
     compat_setenv,
     compat_str,
+    compat_subprocess_Popen,
 )
 from ..postprocessor.ffmpeg import FFmpegPostProcessor, EXT_TO_OUT_FORMATS
 from ..utils import (
@@ -483,7 +484,12 @@ class FFmpegFD(ExternalFD):
 
         self._debug_cmd(args)
 
-        proc = subprocess.Popen(args, stdin=subprocess.PIPE, env=env)
+        # From [1], a PIPE opened in Popen() should be closed, unless
+        # .communicate() is called. Avoid leaking any PIPEs by using Popen
+        # as a context manager (newer Python 3.x and compat)
+        # Fixes "Resource Warning" in test/test_downloader_external.py
+        # [1] https://devpress.csdn.net/python/62fde12d7e66823466192e48.html
+        with compat_subprocess_Popen(args, stdin=subprocess.PIPE, env=env) as proc:
             try:
                 retval = proc.wait()
             except BaseException as e:
@@ -496,7 +502,6 @@ class FFmpegFD(ExternalFD):
                     process_communicate_or_kill(proc, b'q')
                 else:
                     proc.kill()
-                proc.wait()
                 raise
         return retval