deadlock when calling rtpbin.emit("get-internal-session", 0) from python

Submitted by Ben

Link to original bug (#762135)

Description

Created attachment 321363
gdb output when the app deadlock

I have a python3 app that push RTP and RTCP packets through appsrc to rtpbin.
When adding and removing rtp sources fast enough, the app deadlock at sending the gst-internal-session.

slomo comment on the irc channel:
it's ssrc_demux_pad_removed, the free_stream() thing there is doing state changes and stuff with the lock held

self.rtpbin.connect("pad-added", self.on_pad_added)

def on_pad_added(self, element, pad):
session = self.rtpbin.emit("get-internal-session", 0)

Attachment 321363, "gdb output when the app deadlock":
gdb.txt

Version: 1.6.0