WIP: Usubscribe from events in worker thread (PyTango#292)

[reszelaz]

Similarly to #1091, this PR tries to workaround PyTango#292.
This one implements the 3.b option proposed by @schooft in tango-controls/pytango#292 (comment). Thanks!

I tried this PR with sardana-org/sardana#1312 ( which reverts the Sardana workaround and use zombie concept in tests) and it worked for 7 testsuite executions already. Note that the usage of zombie API in tests most probably won't be need if we implement #1092.

[cpascual]

This is making 2 tests to fail:

• test_cleanup_after_polling
• test_cleanup_state_after_polling

[reszelaz]

This is making 2 tests to fail:

• test_cleanup_after_polling
• test_cleanup_state_after_polling

These most probably fail cause I commented the disabling of polling in TangoAttribute._finalUnsubscribeChangeEvents which was not clear to me that it had to be done exactly there. Why not in TangoAttribute.cleanUp?

[reszelaz]

Anyway I have tested it with a typical macro which discovered PyTango#292:

import taurus
from sardana.macroserver.macro import macro


@macro()
def test_dev_gc(self):
    pool = self.door.get_pools()[0]
    moveables = []
    moveables.extend(pool.getElementNamesOfType("motor"))
    moveables.extend(pool.getElementNamesOfType("pseudomotor"))
    channels = []
    channels.extend(pool.getElementNamesOfType("ctexpchannel"))
    channels.extend(pool.getElementNamesOfType("zerodexpchannel"))
    channels.extend(pool.getElementNamesOfType("onedexpchannel"))
    for m in moveables:
        self.print("{}: {}".format(m, taurus.Device(m).getPosition()))
    for ch in channels:
        self.print("{}: {}".format(ch, taurus.Device(ch).getValue()))

And this fails. So 7 consecutive executions of the sardanatestsuite is not an indicator that this workaround works. The above macro is a better way to check it.

So, while executing the macro, the MacroServer hanged with: work_th_bt.txt and work_th_py-bt.txt.

[reszelaz]

The root issue was solved in tango-controls/cppTango#699.
It is available starting from cppTango 9.3.4rc5. Hence I do not foresee to work anymore on this PR.