On Sun, Dec 4, 2016 at 6:50 PM, Emil Dotchevski
I disagree with this design style, which is to say I also disagree with the existing slot/signal style.
As an example, what if we had a system with hundreds of thousands of numerics... each with a particular name. Then imagine a rule set that had to maintain integrity as any particular numeric were to be changed. With slots or synapses, you're forced to search for the object each time before applying the rules. This would bog down quickly as the number of updates per second increased (imagine 100k objects and 2-10k entwined rules being updated 2k times per second. That's a real world scenario)
The search is the price one has to pay for the non-intrusive nature of Synapse. Obviously, when this isn't necessary (and the overhead of the search is significant, as in the real world use case you're referring to) then you can use a different approach.
Why pay the price at all if there is no need? Why use an inefficient algorithm when a more direct approach is available? Additionally, you can achieve algorithmic capabilities otherwise unobtainable using an observer pattern as I've described. For example, a painter's algorithm for updating screen components. Using slots, the manager may be notified to re-paint the window, but the manager would have to maintain some understanding of the paint order to render it properly. Using a map< int, Observer* > where the int is the painting level, observers can hook into the appropriate level and be called in order by simply traversing the map in-order.
That said, in my own use cases the overhead of Synapse has never been significant in comparison to the time it takes to execute the actual connected functions. Note that the search is limited only to connections of the same signal type, and that it can be implemented as a hash, O(1).
Objects should have events they can trigger or subjects they contain/manage which would trigger given a certain situation (value changes, particular event arrives, flag flips, whatever) and the observer(s), being unknown to the original object, would observe the event via a loose coupling mechanism.
This allows for a system to have hundreds or thousands of objects all trigging events at random but only notifying the particular observers that are interested in that instance's event.
This allows for a more flexible system while promoting dependency driven updates... which would result in the best performance for an event notification system.
I've been using such a design since 1990 and posted a rendition of it to this group 3 months ago:
You should request a formal review, if the Boost community finds your
With a small test case, you would rarely see any performance issues. Only at scale would the inefficiencies start to become apparent. In my example (stock feed), if one stock were to change (ie: MSFT), you would be forced to traverse all 5-10k portfolios then search each to see if they own any MSFT to be updated. Assuming less than 100 positions in each portfolio, O(100) is still 6 comparisons for each one. Assuming only 5k portfolios, where 1k actually have a MSFT position, that's still 30,000 searches to find all 1k portfolios. With the subject/observer approach, no search would be required... just directly to the business rule on each object. 30,000 searches from a single tick. Now imagine 2,000 ticks/sec. That's the issue. Of course, after updating the portfolio, you'd have to remember to trigger any associated agents the user has assigned to watch his investments. Which in turn would trigger other actions. This series of events can be easily obtained using a proper subject/observer pattern. library
useful it'll be accepted.
I offered it up along with any nuggets I may have gleaned long the 25+ yrs of experience utilizing such a design across multiple types of projects. If the community has any questions, I'd imagine they'd ask.