* fix ringbuffer thread safety on ARM. fix#715#388
This patch addresses the thread safety problem of `jack_ringbuffer_t`
mentioned in #715 and #388. The overbound read bug caused by this problem
is impossible to reproduce on x86 due to its strong memory ordering, but
it is a problem on ARM and other weakly ordered architectures.
Basically, the main problem is that, on a weakly ordered architecture,
it is possible that the pointer increment after `memcpy` becomes visible
to the other thread before `memcpy` finishes:
memcpy (&(rb->buf[rb->write_ptr]), src, n1);
// vvv can be visible to reading thread before memcpy finishes
rb->write_ptr = (rb->write_ptr + n1) & rb->size_mask;
If this happens, the other thread can read the remaining garbage values
in `rb->buf` due to be overwritten by the unfinished `memcpy`.
To fix this, an explicit pair of release/acquire memory fences [1] is
used to ensure the copy on the other thread *happens after* the `memcpy`
finishes so no garbage values can be read.
[1]: https://preshing.com/20130922/acquire-and-release-fences/
* remove volatile qualifier on ringbuf r/w pointers
The volatile constraints are excess when compiler barriers are present.
It generates unnecessary `mov` instructions when pointers aren't going
to be updated.
* simplify read/write space calculations
This optimization is possible because the buffer size is always a power
of 2. See [1] for details.
[1]: https://github.com/drobilla/zix/pull/1#issuecomment-1212687196
* move acq fences to separate lines
Directories/paths not directly relevant to jackdbus
were intentionally removed from shortlog.
Authorship of the non-jack2dbus code is to be tracked
in jack2 context instead.
This adds a LICENSE file that describes which licenses this project is
licensed under. This is very important, as the project is licensed under
three licenses.
Also added are copyright notices to the wscript files. I added myself as
copyright holder to them, but there are other people who have
contributed to these files which should have their name in the copyright
header. Clearly stating the license of the wscript files should have
been done long ago.
Before this commit the fill_template script used to always
preprocess/install jackd.0 file.
This commit makes preprocessing/installation of jackd.0 man page to
only happen when jackd is configured to be built.
(cherry picked from commit a219673cac80f3f7090abb16ad015e5730587d6b)
luz paz
Daan De Meyer
K
Florian Walpen
Nedko Arnaudov
Karl Linden
Martin Bruset Solberg
Filipe Coelho