Hi, On Thursday 17 May 2007 19:03, Alan Stern wrote: > On Thu, 17 May 2007, Hans Petter Selasky wrote: > > > In Linux, the USB callbacks are generally atomic. Does that answer > > > your question? > > > > Yes. So you protect the callback with a lock to make it atomic? > > No, you don't understand. The callback is atomic because it is not > allowed to sleep. That's what "atomic" means. It has nothing to do > with locking or protection.
And it cannot be interrupted either? > > > > > b) You don't pre-allocate transfers, resulting in > > > > synchronous/blocking calls everywhere, and no-one thinks about what > > > > can happen then :-) > > > > > > Your reasoning is illogical. Why does allocation have to be blocking? > > > > Memory allocation is blocking in that way it might have to flush out > > memory pages to a harddisk, before those pages can be allocated by > > something in the kernel. Of course there exists no-wait options that you > > can pass to "malloc", but I wouldn't rely too much on those flags > > You _can_ rely on the "no-wait" option to prevent the allocation from > sleeping or flushing pages to a disk... > > > unless you are allocating from a > > pre-defined memory pool, where you know that there is memory reserved for > > you. > > ... and you can't rely on "no-wait" to succeed unless, as you say, you > already know there is memory available. But that's also true for > early, blocking allocations; there's nothing special about late, > non-blocking malloc. > > With pre-allocation you might fail at the beginning, and with late > allocation you might fail in the middle. Either way, you fail. So > what's the big deal? There is a greater chance of successing with pre-allocation if you use the wait flag when you malloc? Right? --HPS ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
