Felipe Magno de Almeida wrote:
On 2/7/06, Giovanni Piero Deretta <gpderetta@gmail.com> wrote:
On 2/7/06, Giovanni P. Deretta <gpderetta@gmail.com> wrote:
Ah, btw, at least on posix systems, file descriptors are guaranteed to be allocated contiguously. So you could create a vector as big as the hightest fd, store the list of operations in it and use the socket_impl as a key for an O(1) lookup in the vector.
This is not true of course... I don't know what i was thinking... Anyway, a file descriptor is *usually* a small integer, so on those systems that keep the set mostly contiguous a vector would work and not waste much space.
Why is not true? I think you were right. Although *all* file descriptors are contiguously, which means that other parts of the program may create "holes" in the vector. But it would work alright (I think ACE does this on Posix systems).
After writing the first email I went and checket the SUSv3. No where it says that when the OS generates a new filedesc it needs to reuse the first number available. In pratice i think that most posix systems do (there are many programs that rely on the set being small, think select() ). But consider dup2(), the user may duplicate a socket fd of value 4 with an fd of value 1234567 or whatever. Yes, this is evil, but might actually happen. -- Giovanni P. Deretta