Let's dive into what the problem is here.
First a description of what happens to a task that
is to be executed in a external (but local) process
via the process executor mechanism.
When a task is about to be sent to execute in the
external (but local) process its first cloned, this
is mainly done so that its notification callbacks can
be altered in a safe manner (ie not altering the
original task object to do this) and that clone has
its notifier emptied out.
What replaces the clone's notifier callbacks though
is a new object (that has a __call__ method so it
looks like just another callback) that will send
messages to the parent process (the one that has
the engine in it) over a secure(ish) channel whenever
the local task triggers its notifier notify() method.
This allows for callbacks in the parent process to
get triggered because once the messages recieved the
original tasks notifier object has its notify() method
called (therefore those callbacks do not really know
the task they are getting messages from is executing out
of process).
The issue though is that if the ANY(*) event type is registered
due to how it works in the notifier is that if the child/cloned
notifier has the ANY event type registered and the cloned task
calls notify() with a specific event this will cause the ANY
callback (in the clone) to transmit a message *and* it will
cause the *specific* event callback to also transmit a message
back to the parent process.
On the engine process side it will get 2 messages and trigger
the callbacks 3 times (twice for the specific event callback
because how the local notifier has the ANY callback registered
and one more time when the local process also sends the same
event based on its registration of the ANY event in the child
process).
This is not what is expected (the message rcved on the engine
process should only trigger one callback to get triggered
if the engine process task has no ANY callback registered or two
engine process callbacks to get triggered if the engine process
task has the ANY callback registered).
Closes-Bug: #1537948
Change-Id: I271bf1f23ad73df6c177cf00fd902c4881ba44ae
84c7a7b2c7