The SharedSingleProducerCircularQueue used here has dubious value, This
queue is used to pass commands to the audio thread, such as play/pause/
seek/volume change/etc. We can make do with a simple locked vector, as
we were blocking to enqueue tasks anyways. We can also use an atomic
bool to tell the audio thread when it needs to take a lock on the task
queue, to keep the thread lock-free most of the time.
This commit removes the -Wno-unusued-private-field flag, thus
reenabling the warning. Unused field were either removed or marked
[[maybe_unused]] when unsure.
This avoids static builds putting the "no-op" implementation of
PlaybackStream::create() in the static archive before the strong
implementation later. On ELF (and probably PE/COFF too), a weak
definition in a static archive is chosen and locked-in as the
definition before a strong definition later in the archive.
Before this change, static builds would have no audio support
at all.
The goal here is to ensure we check for audio backends in a way that
makes sense. On macOS, let's just always use Audio Unit (and thus avoid
any checks for Pulse, to reduce needless/confusing build log noise). We
will also only use the Qt audio backend if no other backend was found,
rather than only checking for Pulse.
Instead of having to duplicate the audio stream backend conditions, just
define PlaybackStream::create in each audio backend implementation file.
We provide a weak definition in PlaybackStream.cpp as the fallback.
