“Bad file descriptor” when reading from pipe in the fork process in python3.4

Question

I use python3.4's os.pipe to do IPC bettwen father process and child process, passing the pipe args by os.execlp args

  self.child_pipe_read=int(sys.argv[2])
  self.child_pipe_write=int(sys.argv[3])

...

  os.execlp('python3','python3','child_test.py',str(pid),str(self.child_pipe_read) ,str(self.child_pipe_write))

however,when I use this:

msg=os.read(self.child_pipe_read,32)

throw Error OSError: [Errno 9] Bad file descriptor

and then I try to write to the pipe:

 os.write(self.parent_pipe_write,(msg+'\n').encode())

BrokenPipeError: [Errno 32] Broken pipe

I saw the python3.4's doc,find this:

"Changed in version 3.4: The new file descriptors are now non-inheritable" but I don't know What's the meaning of it? How can I IPC with pipe?

Answer 1

It is considered a security vulnerability to allow FDs to be inherited by default, hence the change for Python 3.4. You must explicitly mark the FD as inheritable by calling os.set_inheritable(fd, True) . Note that this function is new in Python 3.4.