Hi Erik -- please CC me so I can reply (I don't receive messages from LAU directly). I'm quoting manually here: > > I'm trying to cancel an ongoing sf_* I/O operation (from another > Maybe its a bad idea. :-) I don't think so... Issuing large requests, then cancelling as needed gives a process the lowest possible latency for unpredictable seeks (caused e.g. by user commands), while keeping CPU usage low (by avoiding syscall and context switching overhead) > Reading one frame at a time sounds like a bad idea too. 1 frame at a time was an extreme example. The point was that libsndfile doesn't employ a user-space cache, but direct system calls. Reading 10, 100 or 480 frames at a time will still incur syscall overhead (== CPU usage), and progressively larger cancel latencies. > > libsndfile. It would be nice if libsndfile could allow short reads and > > writes via some sf_command parameter. > It does. You can read any number of frames from 1 through to as many > frames as the file contains. I meant "short reads" in kernel-speak sense: read(2) can return a number of bytes less than the number requested when interrupted by a signal (if SA_RESTART is disabled). My proposal was to add a sf_command() parameter that disables the looping behavior of sf_read() on EINTR, and makes it return exactly as many frames as the first read() call manages to get. On second thought, though, this proposal could not possibly work without a userspace (libsndfile) cache, because read() might return incomplete frames, which would need to be processed in a later call. I discovered the virtual I/O in sndfile, and that seems more appropriate. So I withdraw my proposal. > Basically you could define how fine grained you want you interruption > to be and then only read enough frames so that you can interrupt between That was exactly the strategy I originally described as inadequate, due to syscall overhead (in the absence of userspace caching)... > I just checked, and the address you used to post this email to the LAU > list are not subscribed to the libsndfile-users list. Thats why the list > is rejecting your email. That's exactly the problem: I subscribed about two weeks ago, received a confirmation, and sent a message at that time (which received no bounces, but no replies either). Now, the mailserver somehow forgot about me and is rejecting my messages. Or something... > libsndfile questions here (or better yet, the LAD list since this > is really a development question). You're right -- I've realized right after hitting "Send". Please feel free to respond on LAD (but please CC me). I am replying on LAU this one time to clear up the issues that were already brought up, since my original message seemed confusing. -- Dan _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
