This is intended to prevent crashes when unregister_port() modifies the contents of these
two members at the same time that something else is iterating over them.
This can help when running with very low latency and the
initial process callback is [indirectly] expensive.
E.g. load a heavy session the a RPi4, initial setup can pull
in a lot of data, which blocks the bus.
In particular with the ALSA backend this can lead to poll timeout
which effectively stops the backend.
When recover() successfully re-initializes the device,
processing can continue just like after an x-run.
This can happen during initial session load of "expensive"
sessions (in particular on slow systems, e.g. Raspberry Pi)
usually with synths. Worker thread pulls in many external
files in the background which blocks the bus for a long time.
resulting in a poll-timeout.
Previously this was inherited via PBD.
On MacOS/X, this adds
"-undefined dynamic_lookup -flat_namespace"
and various "-framework .." options to linkflags
Without this flag, .dylibs fail to link usually because
of missing `-lintl` (Undefined symbols: "_libintl_dgettext")
On other systems this is a NO-OP:
CFLAGS_OSX, CXXFLAGS_OSX and LINKFLAGS_OSX
are only set on the darwin platform.
This produces synchronous events on Audio and MIDI ports.
One rvent per second, exactly at every second since engine-start.
MIDI: C-4 Note-on/off (1 sample long)
Audio: +1/-1 transition:
+1 in sync with Note-on,
-1 in sync with Note-off
gcc can recognize various regexps in comments. Since C++17 provides
[[fallthrough]], using /* fallthrough */ consistently seems
appropriate until we switch to C++17.
see also https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
Theoretically this could be lock-free by using a queue of device
ports to be added/remove in sync in the process-callback, but
realistically adding/removing devices doesn't have to be rt-safe.
* PortEngine::available() implementation
* AudioEngine::connected() wrapper
Eventually we may re-introduce PortEngine::available along
with a libardour internal port-engine.
