occasional segfault when reinitializing channel that is subscribed to class member function

[bsobhani]

In the following script, when I set use_class_cb to 1, the script segfaults, but when I set use_class_cb to 0 it does not segfault:

import pvaccess
import time


def func_cb(rec):
        monitor.class_cb(rec)
        return


class Monitor:
        def __init__(self):
                self.channel = None
        def class_cb(self, rec):
                return

monitor = Monitor()
use_class_cb = 1
pvname = "nes:neutrons"
while True:
        if monitor.channel is not None:
                monitor.channel.stopMonitor()
        monitor.channel = pvaccess.Channel(pvname)
        if use_class_cb == 1:
                # segfaults sometimes
                monitor.channel.subscribe("monitor_cb", monitor.class_cb)
        else:
                # does not segfault
                monitor.channel.subscribe("monitor_cb", func_cb)
        monitor.channel.startMonitor()
        time.sleep(1)

Note: On my setup, nes:neutrons is a PV that updates frequently (multiple times per second). If I point to this PV it crashes within a few seconds. I tried pointing it to a PV that updates less frequently (once per second), and it took longer to crash (a little less than an hour).

[sveseli]

I was finally able to reproduce this issue (sorry for the long time to respond). The problem is related to the fact that the above code continuously creates new channel instance which in turn destroys the old one.

If you were to take channel creation and subscription outside of the loop. the problem goes away, e.g.:

monitor.channel = pvaccess.Channel(pvname)
monitor.channel.subscribe("monitor_cb", monitor.class_cb)
while True:
...

I'll fix this in the next release.