Prefetch column names in bulk cursor adaptor.

If the remote end of a bulk cursor died, then it was possible
for getColumnNames() to return null, violating the invariant
that it never returns null.  As a result, the application could
crash in strange ways due to an NPE.

Since we are often interested in the column names anyhow, prefetch
them when setting up the bulk cursor adaptor.  This way, a
remote cursor will never return null even if the remote end died.

It is possible for an application to continue to use a remote cursor
even after the provider has died unless it needs to requery it
for some reason.  Of course at that point, bad things will
happen... but usually the app is better prepared for it than
if it just randomly encounters a null array of column names.

This change also optimizes the bulk cursor adaptor to return the
initial cursor window back to the client, potentially saving
an extra RPC.  Because the communication protocol between
the CursorToBulkCursorAdaptor and BulkCursorToCursorAdaptor was
getting a little hard to follow, introduced a new type called
BulkCursorDescriptor to hold all of the necessary parameters.

Deleted several unnecessary IBulkCursor methods that are never
actually called remotely.

Bug: 6168809
Change-Id: I9aaf6f067c6434a575e2fdbf678243d5ad10755f

Author: Jeff Brown

core/java/android/content/ContentProviderNative.java

@@ -17,6 +17,7 @@
 package android.content;
 
 import android.content.res.AssetFileDescriptor;
+import android.database.BulkCursorDescriptor;
 import android.database.BulkCursorNative;
 import android.database.BulkCursorToCursorAdaptor;
 import android.database.Cursor;
@@ -113,20 +114,14 @@ public boolean onTransact(int code, Parcel data, Parcel reply, int flags)
                     if (cursor != null) {
                         CursorToBulkCursorAdaptor adaptor = new CursorToBulkCursorAdaptor(
                                 cursor, observer, getProviderName());
-                        final IBinder binder = adaptor.asBinder();
-                        final int count = adaptor.count();
-                        final int index = BulkCursorToCursorAdaptor.findRowIdColumnIndex(
-                                adaptor.getColumnNames());
-                        final boolean wantsAllOnMoveCalls = adaptor.getWantsAllOnMoveCalls();
+                        BulkCursorDescriptor d = adaptor.getBulkCursorDescriptor();
 
                         reply.writeNoException();
-                        reply.writeStrongBinder(binder);
-                        reply.writeInt(count);
-                        reply.writeInt(index);
-                        reply.writeInt(wantsAllOnMoveCalls ? 1 : 0);
+                        reply.writeInt(1);
+                        d.writeToParcel(reply, Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
                     } else {
                         reply.writeNoException();
-                        reply.writeStrongBinder(null);
+                        reply.writeInt(0);
                     }
 
                     return true;
@@ -369,12 +364,9 @@ public Cursor query(Uri url, String[] projection, String selection,
 
             DatabaseUtils.readExceptionFromParcel(reply);
 
-            IBulkCursor bulkCursor = BulkCursorNative.asInterface(reply.readStrongBinder());
-            if (bulkCursor != null) {
-                int rowCount = reply.readInt();
-                int idColumnPosition = reply.readInt();
-                boolean wantsAllOnMoveCalls = reply.readInt() != 0;
-                adaptor.initialize(bulkCursor, rowCount, idColumnPosition, wantsAllOnMoveCalls);
+            if (reply.readInt() != 0) {
+                BulkCursorDescriptor d = BulkCursorDescriptor.CREATOR.createFromParcel(reply);
+                adaptor.initialize(d);
             } else {
                 adaptor.close();
                 adaptor = null;

core/java/android/database/AbstractCursor.java

@@ -33,10 +33,39 @@
 public abstract class AbstractCursor implements CrossProcessCursor {
     private static final String TAG = "Cursor";
 
-    DataSetObservable mDataSetObservable = new DataSetObservable();
-    ContentObservable mContentObservable = new ContentObservable();
+    /**
+     * @deprecated This is never updated by this class and should not be used
+     */
+    @Deprecated
+    protected HashMap<Long, Map<String, Object>> mUpdatedRows;
+
+    protected int mPos;
+
+    /**
+     * This must be set to the index of the row ID column by any
+     * subclass that wishes to support updates.
+     */
+    protected int mRowIdColumnIndex;
+
+    /**
+     * If {@link #mRowIdColumnIndex} is not -1 this contains contains the value of
+     * the column at {@link #mRowIdColumnIndex} for the current row this cursor is
+     * pointing at.
+     */
+    protected Long mCurrentRowID;
+
+    protected boolean mClosed;
+    protected ContentResolver mContentResolver;
+    private Uri mNotifyUri;
+
+    private final Object mSelfObserverLock = new Object();
+    private ContentObserver mSelfObserver;
+    private boolean mSelfObserverRegistered;
 
-    Bundle mExtras = Bundle.EMPTY;
+    private DataSetObservable mDataSetObservable = new DataSetObservable();
+    private ContentObservable mContentObservable = new ContentObservable();
+
+    private Bundle mExtras = Bundle.EMPTY;
 
     /* -------------------------------------------------------- */
     /* These need to be implemented by subclasses */
@@ -415,30 +444,4 @@ public void onChange(boolean selfChange) {
             }
         }
     }
-
-    /**
-     * @deprecated This is never updated by this class and should not be used
-     */
-    @Deprecated
-    protected HashMap<Long, Map<String, Object>> mUpdatedRows;
-
-    /**
-     * This must be set to the index of the row ID column by any
-     * subclass that wishes to support updates.
-     */
-    protected int mRowIdColumnIndex;
-
-    protected int mPos;
-    /**
-     * If {@link #mRowIdColumnIndex} is not -1 this contains contains the value of
-     * the column at {@link #mRowIdColumnIndex} for the current row this cursor is
-     * pointing at.
-     */
-    protected Long mCurrentRowID;
-    protected ContentResolver mContentResolver;
-    protected boolean mClosed = false;
-    private Uri mNotifyUri;
-    private ContentObserver mSelfObserver;
-    final private Object mSelfObserverLock = new Object();
-    private boolean mSelfObserverRegistered;
 }

core/java/android/database/BulkCursorDescriptor.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.database;
+
+import android.os.Parcel;
+import android.os.Parcelable;
+
+/**
+ * Describes the properties of a {@link CursorToBulkCursorAdaptor} that are
+ * needed to initialize its {@link BulkCursorToCursorAdaptor} counterpart on the client's end.
+ *
+ * {@hide}
+ */
+public final class BulkCursorDescriptor implements Parcelable {
+    public static final Parcelable.Creator<BulkCursorDescriptor> CREATOR =
+            new Parcelable.Creator<BulkCursorDescriptor>() {
+        @Override
+        public BulkCursorDescriptor createFromParcel(Parcel in) {
+            BulkCursorDescriptor d = new BulkCursorDescriptor();
+            d.readFromParcel(in);
+            return d;
+        }
+
+        @Override
+        public BulkCursorDescriptor[] newArray(int size) {
+            return new BulkCursorDescriptor[size];
+        }
+    };
+
+    public IBulkCursor cursor;
+    public String[] columnNames;
+    public boolean wantsAllOnMoveCalls;
+    public int count;
+    public CursorWindow window;
+
+    @Override
+    public int describeContents() {
+        return 0;
+    }
+
+    @Override
+    public void writeToParcel(Parcel out, int flags) {
+        out.writeStrongBinder(cursor.asBinder());
+        out.writeStringArray(columnNames);
+        out.writeInt(wantsAllOnMoveCalls ? 1 : 0);
+        out.writeInt(count);
+        if (window != null) {
+            out.writeInt(1);
+            window.writeToParcel(out, flags);
+        } else {
+            out.writeInt(0);
+        }
+    }
+
+    public void readFromParcel(Parcel in) {
+        cursor = BulkCursorNative.asInterface(in.readStrongBinder());
+        columnNames = in.readStringArray();
+        wantsAllOnMoveCalls = in.readInt() != 0;
+        count = in.readInt();
+        if (in.readInt() != 0) {
+            window = CursorWindow.CREATOR.createFromParcel(in);
+        }
+    }
+}

core/java/android/database/BulkCursorNative.java

@@ -72,26 +72,6 @@ public boolean onTransact(int code, Parcel data, Parcel reply, int flags)
                     return true;
                 }
 
-                case COUNT_TRANSACTION: {
-                    data.enforceInterface(IBulkCursor.descriptor);
-                    int count = count();
-                    reply.writeNoException();
-                    reply.writeInt(count);
-                    return true;
-                }
-
-                case GET_COLUMN_NAMES_TRANSACTION: {
-                    data.enforceInterface(IBulkCursor.descriptor);
-                    String[] columnNames = getColumnNames();
-                    reply.writeNoException();
-                    reply.writeInt(columnNames.length);
-                    int length = columnNames.length;
-                    for (int i = 0; i < length; i++) {
-                        reply.writeString(columnNames[i]);
-                    }
-                    return true;
-                }
-
                 case DEACTIVATE_TRANSACTION: {
                     data.enforceInterface(IBulkCursor.descriptor);
                     deactivate();
@@ -125,14 +105,6 @@ public boolean onTransact(int code, Parcel data, Parcel reply, int flags)
                     return true;
                 }
 
-                case WANTS_ON_MOVE_TRANSACTION: {
-                    data.enforceInterface(IBulkCursor.descriptor);
-                    boolean result = getWantsAllOnMoveCalls();
-                    reply.writeNoException();
-                    reply.writeInt(result ? 1 : 0);
-                    return true;
-                }
-
                 case GET_EXTRAS_TRANSACTION: {
                     data.enforceInterface(IBulkCursor.descriptor);
                     Bundle extras = getExtras();
@@ -217,52 +189,6 @@ public void onMove(int position) throws RemoteException {
         }
     }
 
-    public int count() throws RemoteException
-    {
-        Parcel data = Parcel.obtain();
-        Parcel reply = Parcel.obtain();
-        try {
-            data.writeInterfaceToken(IBulkCursor.descriptor);
-
-            boolean result = mRemote.transact(COUNT_TRANSACTION, data, reply, 0);
-            DatabaseUtils.readExceptionFromParcel(reply);
-
-            int count;
-            if (result == false) {
-                count = -1;
-            } else {
-                count = reply.readInt();
-            }
-            return count;
-        } finally {
-            data.recycle();
-            reply.recycle();
-        }
-    }
-
-    public String[] getColumnNames() throws RemoteException
-    {
-        Parcel data = Parcel.obtain();
-        Parcel reply = Parcel.obtain();
-        try {
-            data.writeInterfaceToken(IBulkCursor.descriptor);
-
-            mRemote.transact(GET_COLUMN_NAMES_TRANSACTION, data, reply, 0);
-            DatabaseUtils.readExceptionFromParcel(reply);
-
-            String[] columnNames = null;
-            int numColumns = reply.readInt();
-            columnNames = new String[numColumns];
-            for (int i = 0; i < numColumns; i++) {
-                columnNames[i] = reply.readString();
-            }
-            return columnNames;
-        } finally {
-            data.recycle();
-            reply.recycle();
-        }
-    }
-
     public void deactivate() throws RemoteException
     {
         Parcel data = Parcel.obtain();
@@ -317,23 +243,6 @@ public int requery(IContentObserver observer) throws RemoteException {
         }
     }
 
-    public boolean getWantsAllOnMoveCalls() throws RemoteException {
-        Parcel data = Parcel.obtain();
-        Parcel reply = Parcel.obtain();
-        try {
-            data.writeInterfaceToken(IBulkCursor.descriptor);
-
-            mRemote.transact(WANTS_ON_MOVE_TRANSACTION, data, reply, 0);
-            DatabaseUtils.readExceptionFromParcel(reply);
-
-            int result = reply.readInt();
-            return result != 0;
-        } finally {
-            data.recycle();
-            reply.recycle();
-        }
-    }
-
     public Bundle getExtras() throws RemoteException {
         if (mExtras == null) {
             Parcel data = Parcel.obtain();

core/java/android/database/BulkCursorToCursorAdaptor.java

@@ -30,34 +30,23 @@ public final class BulkCursorToCursorAdaptor extends AbstractWindowedCursor {
 
     private SelfContentObserver mObserverBridge = new SelfContentObserver(this);
     private IBulkCursor mBulkCursor;
-    private int mCount;
     private String[] mColumns;
     private boolean mWantsAllOnMoveCalls;
+    private int mCount;
 
     /**
      * Initializes the adaptor.
      * Must be called before first use.
      */
-    public void initialize(IBulkCursor bulkCursor, int count, int idIndex,
-            boolean wantsAllOnMoveCalls) {
-        mBulkCursor = bulkCursor;
-        mColumns = null;  // lazily retrieved
-        mCount = count;
-        mRowIdColumnIndex = idIndex;
-        mWantsAllOnMoveCalls = wantsAllOnMoveCalls;
-    }
-
-    /**
-     * Returns column index of "_id" column, or -1 if not found.
-     */
-    public static int findRowIdColumnIndex(String[] columnNames) {
-        int length = columnNames.length;
-        for (int i = 0; i < length; i++) {
-            if (columnNames[i].equals("_id")) {
-                return i;
-            }
+    public void initialize(BulkCursorDescriptor d) {
+        mBulkCursor = d.cursor;
+        mColumns = d.columnNames;
+        mRowIdColumnIndex = DatabaseUtils.findRowIdColumnIndex(mColumns);
+        mWantsAllOnMoveCalls = d.wantsAllOnMoveCalls;
+        mCount = d.count;
+        if (d.window != null) {
+            setWindow(d.window);
         }
-        return -1;
     }
 
     /**
@@ -169,14 +158,6 @@ public boolean requery() {
     public String[] getColumnNames() {
         throwIfCursorIsClosed();
 
-        if (mColumns == null) {
-            try {
-                mColumns = mBulkCursor.getColumnNames();
-            } catch (RemoteException ex) {
-                Log.e(TAG, "Unable to fetch column names because the remote process is dead");
-                return null;
-            }
-        }
         return mColumns;
     }