Fixes issue with AppNap causing stuttering/silence in background

Adds a mac only Activity class that controls the NSProccessInfo
Activity options. This exposes a C++ interface for the
Objective C calls and handles the Activity Id lifecycle. Currently
sets the Activity to background, latency critical, sleep disabled.

Added the Activity calls to main.cpp, starting it in the same
location that Windows priority is set, and ending it right before
the app exits.

Updated Jamulus.pro to add the new files and required lib.

Jamulus.pro

@@ -91,6 +91,8 @@ win32 {
     QT += macextras
     HEADERS += mac/sound.h
     SOURCES += mac/sound.cpp
+    HEADERS += mac/activity.h
+    OBJECTIVE_SOURCES += mac/activity.mm
     RC_FILE = mac/mainicon.icns
     CONFIG += x86
     QMAKE_TARGET_BUNDLE_PREFIX = net.sourceforge.llcon
@@ -107,7 +109,8 @@ win32 {
         -framework CoreAudio \
         -framework CoreMIDI \
         -framework AudioToolbox \
-        -framework AudioUnit
+        -framework AudioUnit \
+        -framework Foundation
 
     # replace coreaudio with jack if requested
     contains(CONFIG, "jackonmac") {

mac/activity.h

@@ -0,0 +1,46 @@
+/******************************************************************************\
+ * Copyright (c) 2004-2020
+ *
+ * Author(s):
+ *  Volker Fischer
+ *
+ ******************************************************************************
+ *
+ * This program is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 2 of the License, or (at your option) any later
+ * version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc.,
+ * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ *
+\******************************************************************************/
+#pragma once
+
+// Forward Delcaration to pointer that holds the activity id
+class CActivityId;
+
+// Reperesents an OSX specific activity. See Managing Activities
+// https://developer.apple.com/documentation/foundation/nsprocessinfo?language=objc
+// This essentially lets us start and stop an Activity frame where we tell the OS
+// that we are Latency Critical and are not performing background tasks.
+class CActivity
+{
+private:
+    CActivityId *pActivity;
+    
+public:
+    CActivity();
+    
+    ~CActivity();
+    
+    void BeginActivity();
+
+    void EndActivity();
+};

mac/activity.mm

@@ -0,0 +1,53 @@
+/******************************************************************************\
+ * Copyright (c) 2004-2020
+ *
+ * Author(s):
+ *  Volker Fischer
+ *
+ ******************************************************************************
+ *
+ * This program is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 2 of the License, or (at your option) any later
+ * version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc.,
+ * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ *
+\******************************************************************************/
+
+#include "activity.h"
+#include <Foundation/Foundation.h>
+
+class CActivityId
+{
+public:
+    id<NSObject> activityId;
+};
+
+CActivity::CActivity() : pActivity(new CActivityId()) {}
+
+CActivity::~CActivity()
+{
+    delete pActivity;
+}
+
+void CActivity::BeginActivity()
+{
+    NSActivityOptions options = NSActivityBackground | NSActivityIdleSystemSleepDisabled | NSActivityLatencyCritical;
+    
+    pActivity->activityId = [[NSProcessInfo processInfo] beginActivityWithOptions: options reason:@"Jamulus provides low latency audio processing and should not be inturrupted by system throttling."];
+}
+
+void CActivity::EndActivity()
+{
+    [[NSProcessInfo processInfo] endActivity: pActivity->activityId];
+    
+    pActivity->activityId = nil;
+}

src/main.cpp

@@ -37,6 +37,9 @@
 #ifdef ANDROID
 # include <QtAndroidExtras/QtAndroid>
 #endif
+#if defined ( __APPLE__ ) || defined ( __MACOSX )
+# include "mac/activity.h"
+#endif
 
 
 // Implementation **************************************************************
@@ -518,7 +521,6 @@ int main ( int argc, char** argv )
         tsConsole << "Qt5 requires a windowing system to paint a JPEG image; image will use SVG" << endl;
     }
     
-
     // Application/GUI setup ---------------------------------------------------
     // Application object
     QCoreApplication* pApp = bUseGUI
@@ -551,6 +553,14 @@ int main ( int argc, char** argv )
     pApp->addLibraryPath ( QString ( ApplDir.absolutePath() ) );
 #endif
     
+#if defined ( __APPLE__ ) || defined ( __MACOSX )
+    // On OSX we need to declare an activity to ensure the process doesn't get
+    // throttled by OS level Nap, Sleep, and Thread Priority systems.
+    CActivity activity;
+
+    activity.BeginActivity();
+#endif
+
     // init resources
     Q_INIT_RESOURCE(resources);
 
@@ -689,6 +699,10 @@ int main ( int argc, char** argv )
         }
     }
     
+    #if defined ( __APPLE__ ) || defined ( __MACOSX )
+        activity.EndActivity();
+    #endif
+
     return 0;
 }