[get_exe_version] Do version probes with <&-

When doing version probes for ffmpeg, do the
equivalent of calling it as:

    ffmpeg -version <&-

Where <&- is shell syntax for closing stdin before calling the
program. This is roughly equivalent to </dev/null without actually
opening /dev/null.

This prevents ffmpeg -version from hanging when run in the background.
Fixes #955.

The reason is that ffmpeg tries to manipulate stdin to set up terminal
characteristic, and that causes the kernel to suspend the parent
process (youtube-dl).

Note that closing stdin is achieved by calling subprocess.Popen() with
stdin set to subprocess.PIPE and without passing any input to
Popen.communicate(). This is somewhat subtle.
pull/8/head
John Hawkinson 8 years ago
parent 69c2d42bd7
commit 00ca755231

@ -1820,6 +1820,7 @@ def get_exe_version(exe, args=['--version'],
try:
out, _ = subprocess.Popen(
[encodeArgument(exe)] + args,
stdin=subprocess.PIPE,
stdout=subprocess.PIPE, stderr=subprocess.STDOUT).communicate()
except OSError:
return False

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