How to make a class object respond to a long stream of event listener callbacks only at the end of the stream of events

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royk 2019-8-13

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回答： royk 2019-8-13

I have an object Obj of a handle class MyClass that listens for "Change" event notifications from other objects.

Obj runs an "update" function when these other objects notify a "Change" event.

Though, when multiple such “Change” events co-occur (namely, appearing in a fast sequence right after the other), then I would like the object to run the "update" function only after the last event (otherwise it is unnecessarily slow).

What would be the recommended way?

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Walter Roberson 2019-8-13

At the time that a particular event is received, how can the code know that it is the last in the series or not?

Matt J 2019-8-13

royk's comment moved here:

I guess that's my question!

I can imagine the last event can be identified by either:

(1) no additional events within a set time frame;

(2) Matlab becomes "not-busy" within a set time frame.

But in any of these options, my problem is that I cannot simply put a "pause" command in the callback function since this will prevent also the continued execution of the calling objects and thereby will delay the upcoming event notifications.

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Answer 1

Guillaume 2019-8-13

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I guess this follows from your previous question.

As there's no matlab not busy kind of notification, I think the only way you could implement this is with a timer. Whenever you receive an update, start or restart a single shot timer and queue whatever needs queing. So it would be something like this:

classdef MasterController < handle
    properties (Access = private)
        updatetimer;
        updatequeue = {};
    end
    %events, etc.
    methods
        %constructor
        function this = MasterController()
            %if MasterController is guaranteed to be a singleton, the timer could be constructed in the property declaration
            %if not, it has to be constructed in the constructor to avoid all instances sharing the same timer
            this.updatetimer = timer('BusyMode', 'queue', 'ExecutionMode', 'singleshot', 'StartDelay', 1, 'TimerFcn', @this.ExecuteQueue);
            %StartDelay specifies how many seconds to wait before executing the queue. If an event occurs within that time, the timer will be reset
        end
        %the update callback
        function CheckIn(this, updatedata)
            %stop timer if running
            if strcmp(this.updatetimer.Running, 'on')
                stop(this.updatetimer);
            end
            this.updatequeue = {this.updatequeue, updatedata};
            %and start timer
            start(this.updatetimer);
        end
    end
    methods (Access = private)
        function ExecuteQueue(this, ~, ~)
            %with matlab being single threaded, we shouldn't have to worry about having items added to the queue while we read the queue
            %nonetheless, we can make a copy of the queue, clear it and work on the copy
            queue = this.updatequeue;
            this.updatequeue = {};
            for queueditem = queue
                %do something with queueditem{1}
            end
        end
    end
end