30 Nov
2015
30 Nov
'15
7:30 a.m.
On 11/30/2015 03:00 PM, Xavier Mendez wrote:
How can you know that no other process is using the same file?
I have not checked the underlying implementation, but I can easily
imagine that there are locks in the kernel.
Keep jack freewheeling in mind. When freewheeling the process callback
needs to wait for i/o to complete.
"worker thread" sounds like LV2. In this case you're good already since
the LV2 worker takes care of this.
On a different note: check async i/o performance first. Paul may chime
in later, I recall that he benchmarked single-threaded, thread-polls and
async i/o for Ardour at some point and opted for the first.
El 30/11/15 a les 14:27, Robin Gareus ha escrit:
I'm pretty sure they do in the current Linux kernel. There'll be an IRQ
once the read is complete.
On 11/30/2015 12:11 PM, Xavier Mendez wrote:
This is going to run on UNIX-like systems, mostly Linux, and I'm
programming in C/C++.
Hello,
I'm wondering whether it's safe to do non-blocking reads or writes from
inside the process callback.
From what I've seen, non-blocking I/O doesn't cause the process to go
into blocked state, and the realtime scheduler should not switch to
another process. But the documentation doesn't seem to allow them:
On which platform? [...] it cannot call functions that might block
for a long time. This
includes all I/O functions (disk, TTY, network), [...]
So, is it safe to use non-blocking I/O in the process callback?
The short answer is:
"If you don’t know how long it will take, don't do it." [1]
All i/o involve syscalls, and then it depends what the kernel does for
the specific system call(s). Asynchronous I/O usually involves signals
at some point which makes it not safe to use.
I wasn't very specific, let me clarify: I'm only going to do some
read(2) or write(2) syscalls on an FD which has O_NONBLOCK set.
AFAIK these don't involve signals... Some
implementation also
involve mutexes to avoid resource conflicts. You'll have to check the
standard-lib and kernel source for the system that you target.
Hmm... Are mutexes a problem if the FD is used exclusively from the
process callback? All moot
anyway. Proper software needs to do error-handling and doing
that in a rt-callback is out of the question. So you need a non-realtime
thread anyway and if you have that you can directly do i/o there.
Error handling is not a problem here, if those syscalls fail I'll simply
deactivate the JACK client.
anyway, using a ringbuffer to decouple i/o is
trivial: e.g.
https://github.com/jackaudio/example-clients/blob/master/capture_client.c
Thanks for the advice, I'm currently using ringbuffers + worker threads
but being able to do this I/O directly in process() would simplify the
code considerably. I'll consider it, though. Thank you for your help,
Xavi
> best,
> robin
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> [1]
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http://www.rossbencina.com/code/real-time-audio-programming-101-time-waits-…
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