I didn't get Thomas's original mail to the list, just Colin's reply, something wrong there? 2011/8/20 Colin Guthrie <gmane at colin.guthr.ie>: > 'Twas brillig, and Thomas Bushnell, BSG at 19/08/11 19:14 did gyre and > gimble: >> Sorry for breaking the threading, but I only just subscribed to the list >> so I can't reply properly. >> >> I'm the origin of the patch recently posted by David Henningsson which >> alters the way locking works. Maarten Bosmans had some questions I'd >> like to address. >> >> The confusing formatting of the diff in core-util.c is just unidiff >> being clever. Basically I created a new function to wrap around fcntl to >> share the common code between pa_lock_fd and pa_read_lock_fd. >> >> I have no objection of course to simply defining it unconditionally and >> using it always. I do not know Windows, so I was trying to make the >> minimally disruptive change. I didn't know that Windows has read locks. So scrap my earlier suggestion to fall back to pa_lock_fd in pa_read_lock_fd, just put an pa_assert_not_reached at the end of pa_read_lock_fd and I'll fix it for Windows later. >> In Unix, promoting a read lock to a write lock converts the lock--it >> does not add another lock--without releasing the readlock in the middle. Fine, we'll use those semantics and I just have to find a way to implement them on Windows. Could you add a comment to pa_read_lock_fd on how it is supposed to be used? >> I am not wedded at all to the specific details of what the generic >> functions in core-util.c do. >> >> The root issue is as David Henningsson explained. By using an exclusive >> lock, pulseaudio creates an unnecessary contention in reading the >> .pulse-cookie file, and because of the less-than-ideal (but quite >> unchangeable) behavior of NFSv3, this forces a thirty-second delay >> anytime two pulse clients try to read the cookie at the same time. >> Switching to a read lock for the read, and only using an exclusive lock >> when the cookie needs to be written (a much rarer operation), avoids >> this problem entirely. Just a random suggestion: these locks look like they are blocking if the file is already locked. Would returning immediately with an error instead be another solution to the NFS problem? > Thanks for the explanation. > > I'm sure the general principle is a good one and one that we'd like to > adopt. Hopefully Maarten can help you come up with a solution that works > for platform :) Colin, were you thinking pre or post 1.0? Maarten
