Add new OOM adjustment for the "previous" process.

This is the process that you had previously been interacting with
in the UI before the current one.  Treating it specially should
allow us to improve the scenario of switching back and forth
between two apps.

Also add API constent for ICS MR1.

Change-Id: Ib3fe4df36b270be11dfd6b7e8d107c9994058a4d

5 files changed, 55 insertions, 7 deletions

diff --git a/api/current.txt b/api/current.txt
index 9d3856698d88..b180f7d56fa8 100644
--- a/api/current.txt
+++ b/api/current.txt
@@ -14399,6 +14399,7 @@ package android.os {
     field public static final int HONEYCOMB_MR1 = 12; // 0xc
     field public static final int HONEYCOMB_MR2 = 13; // 0xd
     field public static final int ICE_CREAM_SANDWICH = 14; // 0xe
+    field public static final int ICE_CREAM_SANDWICH_MR1 = 15; // 0xf
   }
 
   public final class Bundle implements java.lang.Cloneable android.os.Parcelable {
diff --git a/core/java/android/os/Build.java b/core/java/android/os/Build.java
index 17a882de1a8c..7d034940fda2 100644
--- a/core/java/android/os/Build.java
+++ b/core/java/android/os/Build.java
@@ -277,7 +277,7 @@ public class Build {
         public static final int HONEYCOMB_MR2 = 13;
 
         /**
-         * Android 4.0.
+         * October 2011: Android 4.0.
          *
          * <p>Applications targeting this or a later release will get these
          * new changes in behavior:</p>
@@ -309,6 +309,11 @@ public class Build {
          * </ul>
          */
         public static final int ICE_CREAM_SANDWICH = 14;
+
+        /**
+         * Android 4.1.
+         */
+        public static final int ICE_CREAM_SANDWICH_MR1 = 15;
     }
     
     /** The type of build, like "user" or "eng". */
diff --git a/services/java/com/android/server/am/ActivityManagerService.java b/services/java/com/android/server/am/ActivityManagerService.java
index f8a7d6a491e3..310ace0764a6 100644
--- a/services/java/com/android/server/am/ActivityManagerService.java
+++ b/services/java/com/android/server/am/ActivityManagerService.java
@@ -408,6 +408,12 @@ public final class ActivityManagerService extends ActivityManagerNative
     ProcessRecord mHomeProcess;
     
     /**
+     * This is the process holding the activity the user last visited that
+     * is in a different process from the one they are currently in.
+     */
+    ProcessRecord mPreviousProcess;
+    
+    /**
      * Packages that the user has asked to have run in screen size
      * compatibility mode instead of filling the screen.
      */
@@ -8114,6 +8120,7 @@ public final class ActivityManagerService extends ActivityManagerNative
 
         pw.println();
         pw.println("  mHomeProcess: " + mHomeProcess);
+        pw.println("  mPreviousProcess: " + mPreviousProcess);
         if (mHeavyWeightProcess != null) {
             pw.println("  mHeavyWeightProcess: " + mHeavyWeightProcess);
         }
@@ -8212,6 +8219,7 @@ public final class ActivityManagerService extends ActivityManagerNative
             pw.print("    BACKUP_APP_ADJ: "); pw.println(ProcessList.BACKUP_APP_ADJ);
             pw.print("    SERVICE_ADJ: "); pw.println(ProcessList.SERVICE_ADJ);
             pw.print("    HOME_APP_ADJ: "); pw.println(ProcessList.HOME_APP_ADJ);
+            pw.print("    PREVIOUS_APP_ADJ: "); pw.println(ProcessList.PREVIOUS_APP_ADJ);
             pw.print("    SERVICE_B_ADJ: "); pw.println(ProcessList.SERVICE_B_ADJ);
             pw.print("    HIDDEN_APP_MIN_ADJ: "); pw.println(ProcessList.HIDDEN_APP_MIN_ADJ);
             pw.print("    HIDDEN_APP_MAX_ADJ: "); pw.println(ProcessList.HIDDEN_APP_MAX_ADJ);
@@ -8228,6 +8236,7 @@ public final class ActivityManagerService extends ActivityManagerNative
 
         pw.println();
         pw.println("  mHomeProcess: " + mHomeProcess);
+        pw.println("  mPreviousProcess: " + mPreviousProcess);
         if (mHeavyWeightProcess != null) {
             pw.println("  mHeavyWeightProcess: " + mHeavyWeightProcess);
         }
@@ -9009,6 +9018,8 @@ public final class ActivityManagerService extends ActivityManagerNative
                 oomAdj = buildOomTag("bak", "  ", r.setAdj, ProcessList.HIDDEN_APP_MIN_ADJ);
             } else if (r.setAdj >= ProcessList.SERVICE_B_ADJ) {
                 oomAdj = buildOomTag("svcb ", null, r.setAdj, ProcessList.SERVICE_B_ADJ);
+            } else if (r.setAdj >= ProcessList.PREVIOUS_APP_ADJ) {
+                oomAdj = buildOomTag("prev ", null, r.setAdj, ProcessList.PREVIOUS_APP_ADJ);
             } else if (r.setAdj >= ProcessList.HOME_APP_ADJ) {
                 oomAdj = buildOomTag("home ", null, r.setAdj, ProcessList.HOME_APP_ADJ);
             } else if (r.setAdj >= ProcessList.SERVICE_ADJ) {
@@ -9287,12 +9298,13 @@ public final class ActivityManagerService extends ActivityManagerNative
             ProcessList.SYSTEM_ADJ, ProcessList.PERSISTENT_PROC_ADJ, ProcessList.FOREGROUND_APP_ADJ,
             ProcessList.VISIBLE_APP_ADJ, ProcessList.PERCEPTIBLE_APP_ADJ, ProcessList.HEAVY_WEIGHT_APP_ADJ,
             ProcessList.BACKUP_APP_ADJ, ProcessList.SERVICE_ADJ, ProcessList.HOME_APP_ADJ,
-            ProcessList.SERVICE_B_ADJ, ProcessList.HIDDEN_APP_MAX_ADJ
+            ProcessList.PREVIOUS_APP_ADJ, ProcessList.SERVICE_B_ADJ, ProcessList.HIDDEN_APP_MAX_ADJ
         };
         final String[] oomLabel = new String[] {
                 "System", "Persistent", "Foreground",
                 "Visible", "Perceptible", "Heavy Weight",
-                "Backup", "A Services", "Home", "B Services", "Background"
+                "Backup", "A Services", "Home", "Previous",
+                "B Services", "Background"
         };
         long oomPss[] = new long[oomLabel.length];
         ArrayList<MemItem>[] oomProcs = (ArrayList<MemItem>[])new ArrayList[oomLabel.length];
@@ -9714,7 +9726,10 @@ public final class ActivityManagerService extends ActivityManagerNative
         if (app == mHomeProcess) {
             mHomeProcess = null;
         }
-        
+        if (app == mPreviousProcess) {
+            mPreviousProcess = null;
+        }
+
         if (restart) {
             // We have components that still need to be running in the
             // process, so re-launch it.
@@ -13112,6 +13127,17 @@ public final class ActivityManagerService extends ActivityManagerNative
             app.adjType = "home";
         }
 
+        if (adj > ProcessList.PREVIOUS_APP_ADJ && app == mPreviousProcess
+                && app.activities.size() > 0) {
+            // This was the previous process that showed UI to the user.
+            // We want to try to keep it around more aggressively, to give
+            // a good experience around switching between two apps.
+            adj = ProcessList.PREVIOUS_APP_ADJ;
+            schedGroup = Process.THREAD_GROUP_BG_NONINTERACTIVE;
+            app.hidden = false;
+            app.adjType = "previous";
+        }
+
         if (false) Slog.i(TAG, "OOM " + app + ": initial adj=" + adj
                 + " reason=" + app.adjType);
 
@@ -13841,7 +13867,8 @@ public final class ActivityManagerService extends ActivityManagerNative
                     } else {
                         numBg++;
                     }
-                } else if (app.curAdj >= ProcessList.HOME_APP_ADJ) {
+                } else if (app.curAdj >= ProcessList.HOME_APP_ADJ
+                        && app.curAdj != ProcessList.SERVICE_B_ADJ) {
                     numBg++;
                 }
             }
diff --git a/services/java/com/android/server/am/ActivityStack.java b/services/java/com/android/server/am/ActivityStack.java
index 28c3baeb7b63..a47502e4e22d 100644
--- a/services/java/com/android/server/am/ActivityStack.java
+++ b/services/java/com/android/server/am/ActivityStack.java
@@ -1363,6 +1363,13 @@ final class ActivityStack {
                         + ", nowVisible=" + next.nowVisible);
                 }
             }
+
+            if (!prev.finishing && prev.app != null && prev.app != next.app) {
+                // We are switching to a new activity that is in a different
+                // process than the previous one.  Note the previous process,
+                // so we can try to keep it around.
+                mService.mPreviousProcess = prev.app;
+            }
         }
 
         // Launching this app's activity, make sure the app is no longer
diff --git a/services/java/com/android/server/am/ProcessList.java b/services/java/com/android/server/am/ProcessList.java
index f368a7059e53..af7b3141e500 100644
--- a/services/java/com/android/server/am/ProcessList.java
+++ b/services/java/com/android/server/am/ProcessList.java
@@ -38,11 +38,19 @@ class ProcessList {
     // This is a process only hosting activities that are not visible,
     // so it can be killed without any disruption.
     static final int HIDDEN_APP_MAX_ADJ = 15;
-    static int HIDDEN_APP_MIN_ADJ = 8;
+    static int HIDDEN_APP_MIN_ADJ = 9;
 
     // The B list of SERVICE_ADJ -- these are the old and decrepit
     // services that aren't as shiny and interesting as the ones in the A list.
-    static final int SERVICE_B_ADJ = 7;
+    static final int SERVICE_B_ADJ = 8;
+
+    // This is the process of the previous application that the user was in.
+    // This process is kept above other things, because it is very common to
+    // switch back to the previous app.  This is important both for recent
+    // task switch (toggling between the two top recent apps) as well as normal
+    // UI flow such as clicking on a URI in the e-mail app to view in the browser,
+    // and then pressing back to return to e-mail.
+    static final int PREVIOUS_APP_ADJ = 7;
 
     // This is a process holding the home application -- we want to try
     // avoiding killing it, even if it would normally be in the background,