Messages in this thread | | | Date | Sat, 2 Sep 2000 05:25:12 -0700 (PDT) | From | dean gaudet <> | Subject | Re: thread rant |
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On Sat, 2 Sep 2000, Ingo Molnar wrote:
> i dont understand why this is such an important category. If the sharing > is very high between the threads then it makes sense to use 'shared-all > threads'. But frequently the example given are webservers, which often do > not have alot of cross-request shared state.
web *applications* are loaded with cross-request state. there's only so much you can stuff in a cookie, and what application servers typically do is stuff only a session id into the cookie and keep the rest of the application state in memory or on disk. a good example would be a web-based email gateway to an IMAP mail-store. (i.e. think about how to write yahoo mail or hotmail)
web content is easy compared to web applications...
> > file descriptors -- yeesh these are hard, you want some sharing and > > some not sharing. [...] > > well (in Linux) you can specify it on a per-filedescriptor level wether to > share or not to share, and you can pass a filedescriptor to another > process and you can establish it there. Is there any API missing in this > area?
so even if CLONE_FILES is set i can specify i don't want files to be shared? how does that work?
an example of brokenness in the traditional fd API is close-on-exec -- there's a race between open()/socket()/pipe() and fcntl(FD_CLOEXEC) during which if another thread does a fork() it's possible the child will inherit an fd it shouldn't... working around it is painful. the model which NT/OS2 use for creating a new process scales better in the 99.99% case of stdin/out/err -- you only specify those fds you want to keep in the new process.
i know you've done a kick-ass job of making fd allocation not collide a hell of a lot, but it's another synchronization that's unnecessary really.
> > other than TLB/page-table changes is there anything else i'm missing > > which makes SMP and threading "slow"? > > it's not slow, it's 'slower' in the 'common memory allocation' case.
yeah malloc generally sucks because it puts synchronization in when and the avg programmer doesn't realise it. http://www.hoard.org/ is pretty interesting research in this area though.
-dean
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