Tensorflow: Session got stuck after fork

Version: nightly prebuilt for Python2 w/ GPU (just now)

I'm expecting the following code to print "10.0" 3 times, but session.run got stuck in all forked processes.

import tensorflow as tf
import multiprocessing as mp
import os

class Worker(mp.Process):
    def __init__(self, gid):
        self.gid = gid
        super(Worker, self).__init__()

    def run(self):
        G = tf.Graph()
        with G.as_default():
            x = tf.placeholder(tf.float32, shape=[])
            y = x * 2
            sess = tf.Session()
            print sess.run(y, feed_dict={x: 5})

G = tf.Graph()
with G.as_default():
    sess = tf.Session()
    with sess.as_default():
        x = tf.placeholder(tf.float32, shape=[])
        y = x * 2
        print sess.run(y, feed_dict={x: 5})

procs = [Worker(k) for k in range(2)]
for p in procs: p.start()
for p in procs: p.join()

Removing the graph/session in master process will solve the problem. So it seems like once there is a session, we cannot use fork?
The problem exists with and without GPU.

NOTE: this code doesn't terminate normally. You'll probably need to manually kill the forked processes after the master exited.