audio_backend: Merge is_realtime() into client_real_time_priority()

The description of is_realtime() did not match its actual use. And
client_real_time_priority() did not have any description. It was
hard to come up with good descriptions of what they actually did.

Most backends returned true from is_realtime(), but every one except
JACK used the default implementation of client_real_time_priority() that
returned 0 ... which is exactly the same as when is_realtime() returns
false. Just merge them and keep it simple.

libs/ardour/ardour/audio_backend.h

@@ -149,15 +149,10 @@ public:
 	 */
 	virtual std::string name () const = 0;
 
-	/** Return true if the callback from the underlying mechanism/API
+	/** Return true if the backend is JACK */
-	 * (CoreAudio, JACK, ASIO etc.) occurs in a thread subject to realtime
-	 * constraints. Return false otherwise.
-	 */
-	virtual bool is_realtime () const = 0;
-
-	/** Return true if the backed is JACK */
 	virtual bool is_jack () const { return false; }
 
+	/** Return the priority to be set with pbd_set_engine_rt_priority. */
 	virtual int client_real_time_priority () { return 0; }
 
 	/* Discovering devices and parameters */

libs/ardour/audioengine.cc

@@ -1067,11 +1067,7 @@ AudioEngine::start (bool for_latency)
 		return -1;
 	}
 
-	if (_backend->is_realtime ()) {
 	pbd_set_engine_rt_priority (_backend->client_real_time_priority ());
-	} else {
-		pbd_set_engine_rt_priority (0);
-	}
 
 	_running = true;
 

libs/backends/alsa/alsa_audiobackend.cc

@@ -99,12 +99,6 @@ AlsaAudioBackend::name () const
 	return X_("ALSA");
 }
 
-bool
-AlsaAudioBackend::is_realtime () const
-{
-	return true;
-}
-
 std::vector<AudioBackend::DeviceStatus>
 AlsaAudioBackend::enumerate_devices () const
 {

libs/backends/alsa/alsa_audiobackend.h

@@ -125,7 +125,6 @@ class AlsaAudioBackend : public AudioBackend, public PortEngineSharedImpl
 		/* AUDIOBACKEND API */
 
 		std::string name () const;
-		bool is_realtime () const;
 
 		bool use_separate_input_and_output_devices () const { return true; }
 		bool match_input_output_devices_or_none () const { return false; }

libs/backends/coreaudio/coreaudio_backend.cc

@@ -149,12 +149,6 @@ CoreAudioBackend::name () const
 	return X_("CoreAudio");
 }
 
-bool
-CoreAudioBackend::is_realtime () const
-{
-	return true;
-}
-
 std::vector<AudioBackend::DeviceStatus>
 CoreAudioBackend::enumerate_devices () const
 {

libs/backends/coreaudio/coreaudio_backend.h

@@ -160,7 +160,6 @@ class CoreAudioBackend : public AudioBackend, public PortEngineSharedImpl {
 	/* AUDIOBACKEND API */
 
 	std::string name () const;
-	bool is_realtime () const;
 
 	bool use_separate_input_and_output_devices () const { return true; }
 	std::vector<DeviceStatus> enumerate_devices () const;

libs/backends/dummy/dummy_audiobackend.cc

@@ -110,12 +110,6 @@ DummyAudioBackend::name () const
 	return X_("Dummy"); // internal name
 }
 
-bool
-DummyAudioBackend::is_realtime () const
-{
-	return false;
-}
-
 std::vector<AudioBackend::DeviceStatus>
 DummyAudioBackend::enumerate_devices () const
 {

libs/backends/dummy/dummy_audiobackend.h

@@ -194,7 +194,6 @@ class DummyAudioBackend : public AudioBackend, public PortEngineSharedImpl
 		/* AUDIOBACKEND API */
 
 		std::string name () const;
-		bool is_realtime () const;
 
 		bool requires_driver_selection() const { return true; }
 		std::string driver_name () const;

libs/backends/jack/jack_audiobackend.cc

@@ -105,13 +105,6 @@ JACKAudioBackend::available() const
 	return (private_handle() != 0);
 }
 
-bool
-JACKAudioBackend::is_realtime () const
-{
-	GET_PRIVATE_JACK_POINTER_RET (_priv_jack,false);
-	return jack_is_realtime (_priv_jack);
-}
-
 bool
 JACKAudioBackend::requires_driver_selection() const
 {
@@ -882,6 +875,8 @@ int
 JACKAudioBackend::client_real_time_priority ()
 {
 	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, 0);
+	if (!jack_is_realtime (_priv_jack))
+		return 0;
 	return jack_client_real_time_priority (_priv_jack);
 }
 

libs/backends/jack/jack_audiobackend.h

@@ -58,7 +58,6 @@ class JACKAudioBackend : public AudioBackend {
 
 	std::string name() const;
 	void* private_handle() const;
-	bool is_realtime () const;
 
 	bool is_jack () const { return true; }
 

libs/backends/portaudio/portaudio_backend.cc

@@ -118,12 +118,6 @@ PortAudioBackend::name () const
 	return X_("PortAudio");
 }
 
-bool
-PortAudioBackend::is_realtime () const
-{
-	return true;
-}
-
 bool
 PortAudioBackend::requires_driver_selection() const
 {

libs/backends/portaudio/portaudio_backend.h

@@ -99,7 +99,6 @@ class PortAudioBackend : public AudioBackend, public PortEngineSharedImpl {
 		/* AUDIOBACKEND API */
 
 		std::string name () const;
-		bool is_realtime () const;
 
 		bool requires_driver_selection() const;
 		std::string driver_name () const;

libs/backends/pulseaudio/pulseaudio_backend.cc

@@ -332,12 +332,6 @@ PulseAudioBackend::name () const
 	return X_("PulseAudio");
 }
 
-bool
-PulseAudioBackend::is_realtime () const
-{
-	return true;
-}
-
 std::vector<AudioBackend::DeviceStatus>
 PulseAudioBackend::enumerate_devices () const
 {

libs/backends/pulseaudio/pulseaudio_backend.h

@@ -102,7 +102,6 @@ public:
 	/* AUDIOBACKEND API */
 
 	std::string name () const;
-	bool is_realtime () const;
 
 	std::vector<DeviceStatus> enumerate_devices () const;
 	std::vector<float> available_sample_rates (const std::string& device) const;