INetworkStatsSession with lifecycle for caching.

Users outside system_server now explicitly communicate their
lifecycle, which keeps a strong-reference chain to any fully loaded
NetworkStatsCollection histories.

Bug: 6236498
Change-Id: I8e22739b6e89a626b676967a736d7117fd000778

3 files changed, 71 insertions, 30 deletions

diff --git a/services/java/com/android/server/net/NetworkPolicyManagerService.java b/services/java/com/android/server/net/NetworkPolicyManagerService.java
index b0657a6..77addd6 100644
--- a/services/java/com/android/server/net/NetworkPolicyManagerService.java
+++ b/services/java/com/android/server/net/NetworkPolicyManagerService.java
@@ -1740,7 +1740,7 @@ public class NetworkPolicyManagerService extends INetworkPolicyManager.Stub {
 
     private long getTotalBytes(NetworkTemplate template, long start, long end) {
         try {
-            return mNetworkStats.getSummaryForNetwork(template, start, end).getTotalBytes();
+            return mNetworkStats.getNetworkTotalBytes(template, start, end);
         } catch (RuntimeException e) {
             Slog.w(TAG, "problem reading network stats: " + e);
             return 0;
diff --git a/services/java/com/android/server/net/NetworkStatsRecorder.java b/services/java/com/android/server/net/NetworkStatsRecorder.java
index 290bd2c..540f606 100644
--- a/services/java/com/android/server/net/NetworkStatsRecorder.java
+++ b/services/java/com/android/server/net/NetworkStatsRecorder.java
@@ -221,6 +221,11 @@ public class NetworkStatsRecorder {
         if (mLastSnapshot != null) {
             mLastSnapshot = mLastSnapshot.withoutUid(uid);
         }
+
+        final NetworkStatsCollection complete = mComplete != null ? mComplete.get() : null;
+        if (complete != null) {
+            complete.removeUid(uid);
+        }
     }
 
     /**
diff --git a/services/java/com/android/server/net/NetworkStatsService.java b/services/java/com/android/server/net/NetworkStatsService.java
index b847673..f7ba329 100644
--- a/services/java/com/android/server/net/NetworkStatsService.java
+++ b/services/java/com/android/server/net/NetworkStatsService.java
@@ -70,6 +70,7 @@ import android.content.IntentFilter;
 import android.net.IConnectivityManager;
 import android.net.INetworkManagementEventObserver;
 import android.net.INetworkStatsService;
+import android.net.INetworkStatsSession;
 import android.net.LinkProperties;
 import android.net.NetworkIdentity;
 import android.net.NetworkInfo;
@@ -412,40 +413,75 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
     }
 
     @Override
-    public NetworkStatsHistory getHistoryForNetwork(NetworkTemplate template, int fields) {
-        return mDevStatsCached.getHistory(template, UID_ALL, SET_ALL, TAG_NONE, fields);
-    }
+    public INetworkStatsSession openSession() {
+        mContext.enforceCallingOrSelfPermission(READ_NETWORK_USAGE_HISTORY, TAG);
 
-    @Override
-    public NetworkStats getSummaryForNetwork(NetworkTemplate template, long start, long end) {
-        return mDevStatsCached.getSummary(template, start, end);
-    }
+        // return an IBinder which holds strong references to any loaded stats
+        // for its lifetime; when caller closes only weak references remain.
 
-    @Override
-    public NetworkStatsHistory getHistoryForUid(
-            NetworkTemplate template, int uid, int set, int tag, int fields) {
-        // TODO: transition to stats sessions to avoid WeakReferences
-        if (tag == TAG_NONE) {
-            return mUidRecorder.getOrLoadCompleteLocked().getHistory(
-                    template, uid, set, tag, fields);
-        } else {
-            return mUidTagRecorder.getOrLoadCompleteLocked().getHistory(
-                    template, uid, set, tag, fields);
-        }
+        return new INetworkStatsSession.Stub() {
+            private NetworkStatsCollection mUidComplete;
+            private NetworkStatsCollection mUidTagComplete;
+
+            private NetworkStatsCollection getUidComplete() {
+                if (mUidComplete == null) {
+                    mUidComplete = mUidRecorder.getOrLoadCompleteLocked();
+                }
+                return mUidComplete;
+            }
+
+            private NetworkStatsCollection getUidTagComplete() {
+                if (mUidTagComplete == null) {
+                    mUidTagComplete = mUidTagRecorder.getOrLoadCompleteLocked();
+                }
+                return mUidTagComplete;
+            }
+
+            @Override
+            public NetworkStats getSummaryForNetwork(
+                    NetworkTemplate template, long start, long end) {
+                return mDevStatsCached.getSummary(template, start, end);
+            }
+
+            @Override
+            public NetworkStatsHistory getHistoryForNetwork(NetworkTemplate template, int fields) {
+                return mDevStatsCached.getHistory(template, UID_ALL, SET_ALL, TAG_NONE, fields);
+            }
+
+            @Override
+            public NetworkStats getSummaryForAllUid(
+                    NetworkTemplate template, long start, long end, boolean includeTags) {
+                final NetworkStats stats = getUidComplete().getSummary(template, start, end);
+                if (includeTags) {
+                    final NetworkStats tagStats = getUidTagComplete()
+                            .getSummary(template, start, end);
+                    stats.combineAllValues(tagStats);
+                }
+                return stats;
+            }
+
+            @Override
+            public NetworkStatsHistory getHistoryForUid(
+                    NetworkTemplate template, int uid, int set, int tag, int fields) {
+                if (tag == TAG_NONE) {
+                    return getUidComplete().getHistory(template, uid, set, tag, fields);
+                } else {
+                    return getUidTagComplete().getHistory(template, uid, set, tag, fields);
+                }
+            }
+
+            @Override
+            public void close() {
+                mUidComplete = null;
+                mUidTagComplete = null;
+            }
+        };
     }
 
     @Override
-    public NetworkStats getSummaryForAllUid(
-            NetworkTemplate template, long start, long end, boolean includeTags) {
-        // TODO: transition to stats sessions to avoid WeakReferences
-        final NetworkStats stats = mUidRecorder.getOrLoadCompleteLocked().getSummary(
-                template, start, end);
-        if (includeTags) {
-            final NetworkStats tagStats = mUidTagRecorder.getOrLoadCompleteLocked().getSummary(
-                    template, start, end);
-            stats.combineAllValues(tagStats);
-        }
-        return stats;
+    public long getNetworkTotalBytes(NetworkTemplate template, long start, long end) {
+        mContext.enforceCallingOrSelfPermission(READ_NETWORK_USAGE_HISTORY, TAG);
+        return mDevStatsCached.getSummary(template, start, end).getTotalBytes();
     }
 
     @Override