This issue comes from sandbox, not from ctypes.

Using sandbox, execv() C function doesn't close files with FD_CLOEXEC flag if the child program is a static program.

test_ctypes hangs on find_library() in subprocess.Popen._execute_child():
 - create a pipe for the child exception (if any)
 - fork
 - the parent reads this pipe
 - the child calls exec()
 - exec() closes the pipe and the parent continues its work
 - etc.

find_library() runs "ldconfig -p" in a subprocess, and so everything hangs on "the parent reads this pipe" because "exec() closes the pipe and the parent continues its work" doesn't occur.