That's one example of low-hanging fruit. Calling query_info_async is the same thing. Creating a GFileMonitor for a GResourceFile (admittedly nonsense, but arbitrary code that tries to watch any GFile passed into it might hurt) will call query_info_async once every 5 seconds, creating a new thread for each.
If we want to clean this up by playing whack-a-mole and writing a lot of special-case code, we can certainly do that. I'm widely convinced doing so is a waste of time. Another example: for some odd reason, GLocalFileInputStream isn't a pollable output stream, so calling write_async on it spawns a thread, even when it should be using a write poll integrated with the mainloop. Why was this done? I don't know. Should this be fixed? Yes. On Wed, Feb 11, 2015 at 4:10 AM, Philip Withnall <phi...@tecnocode.co.uk> wrote: > On Tue, 2015-02-10 at 10:30 -0800, Jasper St. Pierre wrote: > > One quick example: calling g_file_read_async on a GResourceFile spawns > > a new thread and does a synchronous stream read from a block already > > in memory. > > > > > > It should just be a single g_bytes_ref, but we have three different > > classes created, a thread spawned, and a large amount of locks to do > > the equivalent of memcpy. > > That’s not good at all, and seems like it should be easy to fix by > overriding the read_async vfunc for GResourceFile. Is there a bug filed > about it? > > Philip > > > On Tue, Feb 10, 2015 at 8:49 AM, Jasper St. Pierre > > <jstpie...@mecheye.net> wrote: > > Right now the way g_file_read_async works is by scheduling a > > task on a worker thread, having the worker thread do the async > > read, and then returning a result. > > > > As such, it's impossible to have two async reads done at the > > same time, which is really unfortunate from my understanding. > > If I'm reading a large file, and then a small file, the large > > file needs to fully complete before the small file is > > dispatched from the async queue. > > > > Additionally, when profiling GNOME on ARM, I've been seeing a > > lot of cases of users using g_file_read_async() "just in case" > > for no particular reason, which causes several locks to be > > taken, severely slowing performance. > > > > > > We need to seriously improve our async performance before > > asking people to use it. > > > > > > On Tue, Feb 10, 2015 at 6:48 AM, Lennart Poettering > > <mzta...@0pointer.de> wrote: > > On Tue, 10.02.15 13:59, Philip Withnall > > (phi...@tecnocode.co.uk) wrote: > > > > > > I am pretty sure if you do async IO like gio does > > for every single > > > > file access you'll just complicate your program > > and make it > > > > substantially slower. For small files normal, > > synchronous disk access > > > > is a ton faster than dispatching things to > > background threads, and > > > > back... > > > > > > The problem is that GIO can’t know which accesses > > are to small, local > > > files, and which aren’t. It already optimises reads > > from pollable > > > streams (sockets) by keeping them in the main thread > > and adding them > > > into the main poll() call. > > > > Well, but the developer frequently knows that. He > > knows that the > > config file in ~/.config is not going to be more than > > a few K. And > > that it hence is fine to access it synchronously... > > > > > > Also, glib has wrappers for making mmaping > > available to programs, to > > > > improve seldom-accessed sparse databases > > efficient, do you want to > > > > prohibit that too? > > > > > > No, mmap() is clearly a tool for a different kind of > > problem. If you’re > > > accessing an mmap()ed file, you need to be sure it’s > > local anyway, I > > > think? GMappedFile doesn’t have async versions of > > its methods, > > > presumably for this reason. > > > > mmap() works pretty Ok these days over NFS. Concurrent > > access > > doesn't. But as long as you just want to access > > something, it's > > fine... > > > > That said it's probably not a good idea to use mmap() > > for stuff below > > $HOME... > > > > > As above, how about making that line the distinction > > between calling > > > functions from gstdio.h and using GIO? In the former > > case, you know > > > you’re operating on local files. In the latter, you > > could be operating > > > on files from the moon. > > > > I'd always leave some freedom for the developers. It > > is certainly good > > to document things and push people into the right > > directions, but I > > think there are many cases where the developer should > > have every right > > to prefer sync access for valid reasons, even from the > > main loop... > > > > Lennart > > > > -- > > Lennart Poettering, Red Hat > > _______________________________________________ > > desktop-devel-list mailing list > > desktop-devel-list@gnome.org > > > https://mail.gnome.org/mailman/listinfo/desktop-devel-list > > > > > > > > > > -- > > Jasper > > > > > > > > > > -- > > Jasper > > > > -- Jasper
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