13 messages in com.selenic.mercurial-devel"Instantaneous Notification" on OS X| From | Sent On | Attachments |
|---|---|---|
| Anant Narayanan | Mar 17, 2008 8:22 pm | |
| Aleix Conchillo Flaqué | Mar 18, 2008 1:00 am | |
| Aleix Conchillo Flaqué | Mar 18, 2008 1:00 am | |
| TK Soh | Mar 18, 2008 1:28 am | |
| Peter Arrenbrecht | Mar 18, 2008 1:39 am | |
| Patrick Mézard | Mar 18, 2008 1:42 am | |
| Dirkjan Ochtman | Mar 18, 2008 5:16 am | |
| Vladimir Marek | Mar 18, 2008 6:20 am | |
| Matt Mackall | Mar 18, 2008 7:50 am | |
| Matt Mackall | Mar 18, 2008 7:57 am | |
| Bryan O'Sullivan | Mar 18, 2008 8:32 am | |
| Dirkjan Ochtman | Mar 18, 2008 9:39 am | |
| Anant Narayanan | Mar 18, 2008 12:02 pm |
| Subject: | "Instantaneous Notification" on OS X | |
|---|---|---|
| From: | Dirkjan Ochtman (dirk...@ochtman.nl) | |
| Date: | Mar 18, 2008 5:16:15 am | |
| List: | com.selenic.mercurial-devel | |
Hi,
Anant Narayanan <anant <at> kix.in> writes:
I'm interested in applying for the "Instantaneous Notification" GSoC project idea as listed on your Wiki [1]. I hope this is the right place to discuss SoC project ideas!
Yes, it sure is. Thanks for your interest!
While I'm not familiar with how notifications work in Windows, I have some idea of how things are laid out in the Mac. In OS X 10.4, there is no public API for filesystem changes; although /dev/fsevents is available (which is what Spotlight uses). However, using the fsevents file has several drawbacks (the API is private for a reason) - one badly behaved client is sufficient to spoil it for everyone. The kernel holds all events written to the file in a buffer until all interested applications have been notified. When heavy filesystem activity occurs (eg. when a huge tarball is unpacked or a large application is installed), it is possible that the buffer fills up and events are dropped. This method also requires us to run a daemon that continuously monitors the file, lest we miss certain changes, although this requirement can be overcome with 3rd party wrappers over the fsevents file, like fslogger [2].
In OS X 10.5 (Leopard) however, a public API for filesystem changes called FSEvents [3] has appeared. The kernel does the job of continuously monitoring the fsevents file and writing them to a log, so our application can start at any time and say "What's changed since the last time I asked?". Also, since the API is public (i.e. meant to be used), this seems like the the ideal way to go. There is no chance of us missing events.
I concur.
Using the FSEvents API has one disadvantage when compared to probing / dev/fsvents, it notifies us of directory changes only (much like the older dnotify system in Linux). We still have to scan the directories FSEvents returns and compare them to our cached versions to tell the difference. Hence, the speedup may not be as significant as that gained by inotify on Linux.
On the other hand, we don't have to run our own daemon, which is something of an advantage and makes a lot of things easier.
To sum up, is an FSEvents based (hence 10.5 only) solution appear to something that would interest the Mercurial project? Thanks in advance for your comments :)
I think it's a good idea, certainly. On the other hand, given that, as was pointed out earlier in this thread, some Python API for the FSEvents is already available, I wonder if making inotify work on OS X 10.5 wouldn't be to little work to do in a whole summer (we should make your project worth Google's money). But I like that you've already done some research and seem somewhat familiar with the topic at hand! Maybe adding 10.4 support after all would improve the scope, or maybe the inotify extension could use some spit and polish that you could work on. But I'd like it if Bryan O'Sullivan (who first wrote the inotify extension) could weigh in on these things.
Again, thanks for your interest!
Cheers,
Dirkjan