> but couldn't MoI use one thread per object when doing such operation ?
Hi Erwan - well the way joining works is not so much on a per-object basis as it is a processing of all the open edges.
The tricky part is that also some edges may be modified during the join process, for example when 2 are glued together, or when an edge is split into multiple edges.
Algorithms that do modifications in the middle of them tend to be more difficult to break apart into parallel tasks that can be handled by multiple threads.
The other thing is that something like "one thread per entity" really doesn't work very well, because that actually creates too many threads to be optimal - to make best use of resources there shouldn't be more threads than CPUs. So the way it usually needs to work is to maintain a kind of queue of work items and parcel those work items out to be processed on different threads.
It is not typically a very easy task to take a chunk of existing code that is not built with this in mind and then change it to do that... It tends to require a significant rewrite of the code, not just a minor modification.
- Michael
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