[openbeos] Re: Threading and File Descriptors
- From: "Michael Phipps" <mphipps1@xxxxxxxxxxxxxxxx>
- To: openbeos@xxxxxxxxxxxxx
- Date: Sun, 18 Aug 2002 23:00:30 -0400
>would it be so complex ?
>what about having the first part of the array static, and only add parts
>if we really need to ?
>struct desc {
>long count;
>struct desc *next;
>foobar descs[0];
>}
>
>with the first would be inlined in process descriptors or such, and a FOREACH
>macro would do
>
>
>({
>foobar *fd;
>struct desc *current = &proc[i].fd;
>while (current) {
>int i;
>for (i=0; i < current->count; i++) {
>if (compare(current->descs[i], d))
> goto found;
>}
>current = current->next;
>}
>NULL;
>
>found:
>
>current->descs[i];
>})
>
>Of course that's not even quite O(1), and hashing would be harder...
>but in the usual case we would not need anny malloc() since the first block
>is inlined, and the overhead isn't big.
I have seen this before. The problem is deciding what count should be.
Pretend that you are the kernel for a minute. We allocate (say) 5 file
descriptors
in that first block (that is inline). You get a request for another one (#6).
Obviously you have to make a new block. How many should you allocate?
Truth is, we don't know. It could be an app that uses 6. Or 600. There is no
real way to know.
>What about using fixed size arrays, with sizes tweakable at boot
>(in ~/config/settings/kernel/drivers/kernel) ?
>would be as fast, just need a malloc(), still simple code...
>and in case we want to run IceCast for 10000 users just change the MAX_FD
>in the kernel prefs and reboot :)
Very Linux. :-/ Probably better than the way that Be had it (you get N of them,
period),
but still not the way that I would like to do it.
>Or we could as well be able to change some (MAX_FD) at runtime, so increasing
>it just before running critical progs (there is a defined interface for this,
>called ulimit()).
This is more tempting.
>Of course it's not as good as if the system would deal itself with this...
>We must keep in mind we are building a desktop OS, not a server :^)
Yes. But sometimes users want to do these things, too. And for the system to
fail
(as R5 will, I think) on too many is far from ideal.
>Also remember MAX_FD is defined in POSIX headers, so dynamic growing is maybe
>not worth it.
But what if someone uses the Storage Kit?
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