CODEWITHSUNDEEP
c++linux
Translucent Pain
Translucent Pain

Reputation: 1551

Is this an appropriate use for shared_ptr?

Project: typical chat program. Server must receive text from multiple clients and fan each input out to all clients.

In the server I want to have each client to have a struct containing the socket fd and a std::queue. Each structure will be on a std::list.

As input is received from a client socket I want to iterate over the list of structs and put new input into each client struct's queue. A string is new[ed] because I don't want copies of the string multiplied over all the clients. But I also want to avoid the headache of have multiple pointers to the string spread out and deciding when it is time to finally delete the string.

Is this an appropriate occassion for a shared pointer? If so, is the shared_ptr incremented each time I push them into the queue and decremented when I pop them from the queue?

Thanks for any help.

Upvotes: 0

Views: 301

Answers (2)

Ben Voigt
Ben Voigt

Reputation: 283733

This is a case where a pseudo-garbage collector system will work much better than reference counting.

You need only one list of strings, because you "fan every input out to all clients". Because you will add to one end and remove from the other, a deque is an appropriate data structure.

Now, each connection needs only to keep track of the index of the last string it sent. Periodically (every 1000th message received, or every 4MB received, or something like that), you find the minimum of this index across all clients, and delete strings up to that point. This periodic check is also an opportunity to detect clients which have fallen far behind (possible broken connection) and recover. Without this check, a single stuck client will cause your program to leak memory (even under the reference counting scheme).

This scheme is several times less data than reference counting, and also removes one of the major points of cache contention (reference counts must be written from multiple threads, so they ruin performance). If you aren't using threads, it'll still be faster.

Upvotes: 4

David Schwartz
David Schwartz

Reputation: 182819

That is an appropriate use of a shared_ptr. And yes, the use count will be increment because a new shared_ptr will be create to push.

Upvotes: 2

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