Activity Manager changes the scheduling group of processes.

The algorithm for this is currently very simple: all persistent processes are
always in the normal scheduling group, all other processes are normal if their
oom_adj is as good or better than VISIBLE, otherwise they are in the background
group.

Note that this currently results in a fair number of log messages about not
being able to change the group, since the system process does not have
permission to do so.  Once a kernel fix is in, these will go away and the code
will start working.

core/java/android/app/ActivityThread.java

@@ -1513,6 +1513,18 @@ public final class ActivityThread {
             queueOrSendMessage(H.PROFILER_CONTROL, path, start ? 1 : 0);
         }
 
+        public void setSchedulingGroup(int group) {
+            // Note: do this immediately, since going into the foreground
+            // should happen regardless of what pending work we have to do
+            // and the activity manager will wait for us to report back that
+            // we are done before sending us to the background.
+            try {
+                Process.setProcessGroup(Process.myPid(), group);
+            } catch (Exception e) {
+                Log.w(TAG, "Failed setting process group to " + group, e);
+            }
+        }
+        
         @Override
         protected void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
             long nativeMax = Debug.getNativeHeapSize() / 1024;

core/java/android/app/ApplicationThreadNative.java

@@ -331,6 +331,14 @@ public abstract class ApplicationThreadNative extends Binder
             profilerControl(start, path);
             return true;
         }
+        
+        case SET_SCHEDULING_GROUP_TRANSACTION:
+        {
+            data.enforceInterface(IApplicationThread.descriptor);
+            int group = data.readInt();
+            setSchedulingGroup(group);
+            return true;
+        }
         }
 
         return super.onTransact(code, data, reply, flags);
@@ -672,5 +680,14 @@ class ApplicationThreadProxy implements IApplicationThread {
                 IBinder.FLAG_ONEWAY);
         data.recycle();
     }
+    
+    public void setSchedulingGroup(int group) throws RemoteException {
+        Parcel data = Parcel.obtain();
+        data.writeInterfaceToken(IApplicationThread.descriptor);
+        data.writeInt(group);
+        mRemote.transact(SET_SCHEDULING_GROUP_TRANSACTION, data, null,
+                IBinder.FLAG_ONEWAY);
+        data.recycle();
+    }
 }
 

core/java/android/app/IApplicationThread.java

@@ -87,7 +87,8 @@ public interface IApplicationThread extends IInterface {
     void scheduleActivityConfigurationChanged(IBinder token) throws RemoteException;
     void requestPss() throws RemoteException;
     void profilerControl(boolean start, String path) throws RemoteException;
-
+    void setSchedulingGroup(int group) throws RemoteException;
+    
     String descriptor = "android.app.IApplicationThread";
 
     int SCHEDULE_PAUSE_ACTIVITY_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION;
@@ -117,4 +118,5 @@ public interface IApplicationThread extends IInterface {
     int SCHEDULE_RELAUNCH_ACTIVITY_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION+25;
     int REQUEST_PSS_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION+26;
     int PROFILER_CONTROL_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION+27;
+    int SET_SCHEDULING_GROUP_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION+28;
 }