CODEWITHSUNDEEP
cposix-select
ijw
ijw

Reputation: 4526

select() in C: the Rosetta stone?

Mostly select() is straightforward in terms of what flags get set:

But there are plenty of exceptions (or, perhaps, nontrivial extensions) to this rule: 'w' is set for a nonblocking connect that's completed, 'r' is set for a listen() with a pending accept(), and so on.

Has anyone found a straightforward list of what flags get set in what circumstances?

Upvotes: 2

Views: 166

Answers (2)

Sumit Kumar
Sumit Kumar

Reputation: 160

reference for select, which provide suggestion for usage of select

http://man7.org/linux/man-pages/man2/select_tut.2.html

Upvotes: 0

Some programmer dude
Some programmer dude

Reputation: 409422

From this reference page:

A descriptor shall be considered ready for reading when a call to an input function with O_NONBLOCK clear would not block, whether or not the function would transfer data successfully. (The function might return data, an end-of-file indication, or an error other than one indicating that it is blocked, and in each of these cases the descriptor shall be considered ready for reading.)

A descriptor shall be considered ready for writing when a call to an output function with O_NONBLOCK clear would not block, whether or not the function would transfer data successfully.

If a socket has a pending error, it shall be considered to have an exceptional condition pending. Otherwise, what constitutes an exceptional condition is file type-specific.

Except for descriptors in the exceptional set, it's pretty clear. If a blocking descriptor (no matter if it's a file, a socket, or some other descriptor) will not block, then it's marked as ready in its respective set. Accepting and receiving are "read" operations, while connection and writing are "write" operations.

The only problematic thing are the exceptional states, which depends on the type of descriptor you pass in the set.

Upvotes: 2

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