Typhos Suite Segfault on close

[ZLLentz]

Expected Behavior

No segfaults

Current Behavior

If I open a positioner row widget's expert screen (non-row widget), then close this screen, then close the whole GUI, I get a segfault on the pv cleanup steps.

GDB excerpt when looking at the core dump:

Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00005633876f5470 in ?? ()
[Current thread is 1 (Thread 0x7f9470233740 (LWP 16795))]
(gdb)
(gdb) py-bt
Traceback (most recent call first):
  File "/cds/group/pcds/pyps/conda/py39/envs/pcds-5.8.4/lib/python3.9/site-packages/epics/ca.py", line 1896, in clear_subscription
    return libca.ca_clear_subscription(event_id)
  File "/cds/group/pcds/pyps/conda/py39/envs/pcds-5.8.4/lib/python3.9/site-packages/epics/ca.py", line 670, in wrapper
    status = fcn(*args, **kwds)
  File "/cds/group/pcds/pyps/conda/py39/envs/pcds-5.8.4/lib/python3.9/site-packages/epics/ca.py", line 546, in wrapper
    return fcn(*args, **kwds)
  File "/cds/group/pcds/pyps/conda/py39/envs/pcds-5.8.4/lib/python3.9/site-packages/epics/pv.py", line 353, in _clear_auto_monitor_subscription
    ca.clear_subscription(evid)
  File "/cds/group/pcds/pyps/conda/py39/envs/pcds-5.8.4/lib/python3.9/site-packages/epics/pv.py", line 46, in wrapped
    return func(self, *args, **kwargs)
  File "/cds/group/pcds/pyps/conda/py39/envs/pcds-5.8.4/lib/python3.9/site-packages/epics/pv.py", line 1152, in disconnect
    self._clear_auto_monitor_subscription()
  File "/cds/group/pcds/pyps/conda/py39/envs/pcds-5.8.4/lib/python3.9/site-packages/epics/pv.py", line 46, in wrapped
    return func(self, *args, **kwargs)
  File "/cds/group/pcds/pyps/conda/py39/envs/pcds-5.8.4/lib/python3.9/site-packages/pydm/data_plugins/epics_plugins/pyepics_plugin_component.py", line 248, in                                                                                                                                 close
    self.pv.disconnect()
  File "/cds/group/pcds/pyps/conda/py39/envs/pcds-5.8.4/lib/python3.9/site-packages/pydm/data_plugins/plugin.py", line 218, in remove_listener
    self.close()
  File "/cds/group/pcds/pyps/conda/py39/envs/pcds-5.8.4/lib/python3.9/site-packages/pydm/data_plugins/plugin.py", line 317, in remove_connection
    self.connections[connection_id].remove_listener(channel, destroying=destroying)
  File "/cds/group/pcds/pyps/conda/py39/envs/pcds-5.8.4/lib/python3.9/site-packages/pydm/widgets/channel.py", line 164, in disconnect
    plugin.remove_connection(self, destroying=destroying)
  File "/cds/group/pcds/pyps/conda/py39/envs/pcds-5.8.4/lib/python3.9/site-packages/pydm/widgets/base.py", line 103, in widget_destroyed
    ch.disconnect(destroying=True)
  <built-in function _qtcore_cleanup>
(gdb) bt
#0  0x00005633876f5470 in ?? ()
#1  0x00007f9459ba11c0 in ca_client_context::eliminateExcessiveSendBacklog (this=0x5633858569e0, guard=..., chan=...) at ../ca_client_context.cpp:795
#2  0x00007f9459ba12e3 in oldChannelNotify::eliminateExcessiveSendBacklog (guard=..., this=0x5633876d6460) at ../oldAccess.h:483
#3  ca_clear_subscription (pMon=0x7f9400002b80) at ../ca_client_context.cpp:765
#4  0x00007f946885da4a in ffi_call_unix64 () from /cds/group/pcds/pyps/conda/py39/envs/pcds-5.8.4/lib/python3.9/lib-dynload/../../libffi.so.8
#5  0x00007f946885cfea in ffi_call_int () from /cds/group/pcds/pyps/conda/py39/envs/pcds-5.8.4/lib/python3.9/lib-dynload/../../libffi.so.8
#6  0x00007f946886bf59 in _call_function_pointer (argtypecount=<optimized out>, argcount=1, resmem=0x7fff3fda9440, restype=<optimized out>, atypes=<optimized out>, avalues=<optimized out>, pProc=0x7f9459ba12a0 <ca_clear_subscription(evid)>, flags=4353)
    at /usr/local/src/conda/python-3.9.18/Modules/_ctypes/callproc.c:920

Possible Solution

• Figure out if/why the pydm channels get deallocated an extra time

Steps to Reproduce (for bugs)

1. Open a screen with a positioner row widget
2. Click expert screen
3. Close expert screen
4. Close main screen

Context

• Low impact, just annoying and scary to see a segfault message in your python code
• I'm testing some other fixes and stumbled upon this one and decided to briefly investigate

Your Environment

pcds-5.8.2

[tangkong]

I assume this is due to pydm trying to remove a connection from a widget that no longer exists? Presumably the one that you closed manually?

This is what the core dump kinda looks like to me but these things are always kinda sneaky

[ZLLentz]

I think so, but I suspect there is something we can do here so that pydm knows not to do this.