CODEWITHSUNDEEP
c#iosunity-game-enginegarbage-collection.net-3.5
Nic Foster
Nic Foster

Reputation: 2894

C# .NET 3.5: Memory Pool, know when object is released?

I'm in a situation where I'm having to create thousands of objects at once, and the cost of instantiating the objects and garbage collecting them is impacting the performance of the application, and the impact of the garbage collector running hurts the performance more since this is on older hardware, so I'm mostly trying to prevent the creation of garbage. I believe a memory pool would solve my issue but I'm not sure how the memory pool would know when a resource in the pool was freed up for re-use. The tricky part is that receiver of objects from the pool end up passing that object around throughout the program and it would be very difficult to know when it could be manually freed up. I'd like it to be like a WeakReference, where I could know when nobody was using it anymore. But my understanding is that if I use a WeakReference in the memory pool then it would eventually get garbage collected from the pool itself and I need these objects to remain pretty much forever so they'll continue to get recycled. Sometimes the program can go for awhile without needing the objects so I imagine the garbage collector would collect them before the next time when they were needed and that would then trigger another performance hit as another thousand of these objects were made.

Is there a way I can make sure these objects are never collected, but know when there are no references to them aside from the memory pool itself? Do I need to implement reference counting for these objects somehow?

I've been googling for a couple of hours now and have seen no implementation of a Memory Pool that doesn't require the user to let the memory pool know when they're done with it. I find it hard to believe there is no way to do this in C#.

Upvotes: 1

Views: 794

Answers (1)

Jakub Lortz
Jakub Lortz

Reputation: 14894

Is there a way I can make sure these objects are never collected, but know when there are no references to them aside from the memory pool itself?

Usually an object pool only holds references to available objects (you can check ObjectPool implementation in Roslyn). With that in mind, you can use the finalizer to resurrect the object and return it to the pool when it is unreachable.

However, I don't think it will improve performance. The whole pool will very soon reach generation 2, so the unreachable objects will need a full garbage collection to be returned to the pool. Depending on the memory usage pattern in your program, it might not happen very often. You can GC.Collect() and GC.WaitForPendingFinalizers() of course, but it will also hurt performance. You can try it out and check if it helps.

Another problem is the design - your objects are coupled to the pool.

I'd rather try to return the objects to the pool explicitly. Remember that not all objects have to be returned. If there are no more available objects, the pool can create new ones. The ones that were not returned will just be garbage collected. Check if there are some code paths where you are sure the objects are not needed anymore. If you can't find any, try to refactor your code.

Upvotes: 2

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