Demonstration of pv reference leak

1_pv_leak.py

import epics,gc

name1 = "c1v0:UPTIME"
name2 = "c2v0:UPTIME"
name3 = "c3v0:UPTIME"

def report_usage():
    epics.ca.show_cache()
    # use the gc's debugging features to look for leaked PV objects
    gc.collect()
    print("Live PV object count: %d" % len([o for o in gc.get_objects() if type(o) == epics.PV]))
    print("")

def do_some_stuff():
    p = epics.PV(name1)
    p = epics.PV(name2)
    p = epics.PV(name3)
    p = None
    report_usage()

do_some_stuff()
do_some_stuff()
do_some_stuff()

2 Output from master branch

#  PVName        ChannelID/Context Connected?
#--------------------------------------------
 c2v0:UPTIME     c_long(47668984)/47633616  False
 c1v0:UPTIME     c_long(47668928)/47633616  False
 c3v0:UPTIME     c_long(47669040)/47633616  False
Live PV object count: 3

#  PVName        ChannelID/Context Connected?
#--------------------------------------------
 c2v0:UPTIME     c_long(47668984)/47633616  False
 c1v0:UPTIME     c_long(47668928)/47633616  False
 c3v0:UPTIME     c_long(47669040)/47633616  False
Live PV object count: 6

#  PVName        ChannelID/Context Connected?
#--------------------------------------------
 c2v0:UPTIME     c_long(47668984)/47633616  False
 c1v0:UPTIME     c_long(47668928)/47633616  False
 c3v0:UPTIME     c_long(47669040)/47633616  False
Live PV object count: 9

3 Output from fix branch

#  PVName        ChannelID/Context Connected?
#--------------------------------------------
 c2v0:UPTIME     c_long(31308984)/31271728  False
 c1v0:UPTIME     c_long(31308928)/31271728  False
 c3v0:UPTIME     c_long(31309040)/31271728  False
Live PV object count: 0

#  PVName        ChannelID/Context Connected?
#--------------------------------------------
 c2v0:UPTIME     c_long(31308984)/31271728  False
 c1v0:UPTIME     c_long(31308928)/31271728  False
 c3v0:UPTIME     c_long(31309040)/31271728  False
Live PV object count: 0

#  PVName        ChannelID/Context Connected?
#--------------------------------------------
 c2v0:UPTIME     c_long(31308984)/31271728  False
 c1v0:UPTIME     c_long(31308928)/31271728  False
 c3v0:UPTIME     c_long(31309040)/31271728  False
Live PV object count: 0