CODEWITHSUNDEEP
cioposix-select
Miroslav Trninic
Miroslav Trninic

Reputation: 3451

Is C select() function deprecated?

I am reading a book about network progamming in C. It is from 2004. In the example code, author is using select C function to accept multiple connections from the client. Is that function deprecated today?

I see that there are different ways to accept multiplexed I/O like poll and epoll. What are the advantages?

Upvotes: 4

Views: 1188

Answers (3)

Jack O'Connor
Jack O'Connor

Reputation: 10926

It depends on what you mean by "deprecated". The glibc man page for select says the following right at the top:

WARNING: select() can monitor only file descriptors numbers that are less than FD_SETSIZE (1024)—an unreasonably low limit for many modern applications—and this limitation will not change. All modern applications should instead use poll or epoll, which do not suffer this limitation.

When your documentation starts with a warning not to use a certain function, I think it's fair to call that function "deprecated". However, sometimes that term implies that a function is going to be removed in the near future, and select is certainly not going to be removed.

Upvotes: 0

hdante
hdante

Reputation: 8030

It's not deprecated in its behavior, but its design may have performance issues. For example, linux epoll() documentation states:

API can be used either as an edge-triggered or a level-triggered inter‐ face and scales well to large numbers of watched file descriptors.

Since the efficient alternatives are specific to each operating system, an option better than directly using select() is to use a cross platform multiplexing library (which uses the best implementation available), examples being:

If you're developing for a specific operating system, use the recommended implementation for high performance applications.

However, since some people don't like current libraries for I/O multiplexing (due to "being ugly"), select is still a viable alternative.

Upvotes: 4

Karoly Horvath
Karoly Horvath

Reputation: 96286

It's not deprecated, and lots of programs rely on it.

It's just not the best tool as it has some limitations:

  • The number of file descriptors is limited (OS specific, usually possible to increase it with kernel recompiling).
  • Doesn't scale well (with lots of fds): the whole FD set must be maintained, and re-initialized as select manipulates it.

Feel free to use it if these aren't relevant for you. Otherwise use poll/libevent if you're looking for a cross-platform solution, or in some rare-cases epoll/kqueue for platform specific optimized solutions.

Upvotes: 8

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