Closing POSIX.FILE.popen
Files create using posix popen must be closed with pclose rather than fclose - see POPEN(3) manual (http://man7.org/linux/man-pages/man3/popen.3.html).
However, from vala posix.vapi fclose is used:
[CCode (cname = "FILE", free_function = "fclose", cheader_filename = "stdio.h")]
Using fclose instead of pclose means that the process at the other end of the pipe doesn't get reaped, so it stays zombied - source: https://cboard.cprogramming.com/cplusplus-programming/97147-pclose-vs-fclose.html