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Commit f85f5b21 authored by Christopher Tate's avatar Christopher Tate
Browse files

Provide SharedPreferences coherence guarantees for BackupAgent 

SharedPreferences uses deferred writes internally, and the public
API doesn't allow apps to explicitly synchronize with this, so the
backup/restore implementation needs to take a little care to make
sure that the app process isn't killed before the deferred writes
land on disk.  This parallels the coherence guarantees around
SharedPreference that the Activity and Service lifecycles provide.

Bug 8659368

Change-Id: I853e54f9fb0d2d260dbe6e40d640959f998092df
parent 7f6fc129

core/java/android/app/backup/BackupAgent.java

+48 −0
Original line number Diff line number Diff line
@@ -17,12 +17,15 @@ 
package android.app.backup;



import android.app.IBackupAgent;

import android.app.QueuedWork;

import android.app.backup.IBackupManager;

import android.content.Context;

import android.content.ContextWrapper;

import android.content.pm.ApplicationInfo;

import android.os.Binder;

import android.os.Handler;

import android.os.IBinder;

import android.os.Looper;

import android.os.ParcelFileDescriptor;

import android.os.Process;

import android.os.RemoteException;
@@ -33,6 +36,7 @@ import java.io.FileOutputStream; 
import java.io.IOException;

import java.util.HashSet;

import java.util.LinkedList;

import java.util.concurrent.CountDownLatch;



import libcore.io.ErrnoException;

import libcore.io.Libcore;
@@ -122,6 +126,32 @@ public abstract class BackupAgent extends ContextWrapper { 
    /** @hide */

    public static final int TYPE_SYMLINK = 3;



    Handler mHandler = null;



    class SharedPrefsSynchronizer implements Runnable {

        public final CountDownLatch mLatch = new CountDownLatch(1);



        @Override

        public void run() {

            QueuedWork.waitToFinish();

            mLatch.countDown();

        }

    };



    // Syncing shared preferences deferred writes needs to happen on the main looper thread

    private void waitForSharedPrefs() {

        if (mHandler == null) {

            mHandler = new Handler(Looper.getMainLooper());

        }



        final SharedPrefsSynchronizer s = new SharedPrefsSynchronizer();

        mHandler.postAtFrontOfQueue(s);

        try {

            s.mLatch.await();

        } catch (InterruptedException e) { /* ignored */ }

    }





    public BackupAgent() {

        super(null);

    }
@@ -542,6 +572,11 @@ public abstract class BackupAgent extends ContextWrapper { 
                Log.d(TAG, "onBackup (" + BackupAgent.this.getClass().getName() + ") threw", ex);

                throw ex;

            } finally {

                // Ensure that any SharedPreferences writes have landed after the backup,

                // in case the app code has side effects (since apps cannot provide this

                // guarantee themselves).

                waitForSharedPrefs();



                Binder.restoreCallingIdentity(ident);

                try {

                    callbackBinder.opComplete(token);
@@ -569,6 +604,9 @@ public abstract class BackupAgent extends ContextWrapper { 
                Log.d(TAG, "onRestore (" + BackupAgent.this.getClass().getName() + ") threw", ex);

                throw ex;

            } finally {

                // Ensure that any side-effect SharedPreferences writes have landed

                waitForSharedPrefs();



                Binder.restoreCallingIdentity(ident);

                try {

                    callbackBinder.opComplete(token);
@@ -586,6 +624,10 @@ public abstract class BackupAgent extends ContextWrapper { 


            if (DEBUG) Log.v(TAG, "doFullBackup() invoked");



            // Ensure that any SharedPreferences writes have landed *before*

            // we potentially try to back up the underlying files directly.

            waitForSharedPrefs();



            try {

                BackupAgent.this.onFullBackup(new FullBackupDataOutput(data));

            } catch (IOException ex) {
@@ -595,6 +637,9 @@ public abstract class BackupAgent extends ContextWrapper { 
                Log.d(TAG, "onBackup (" + BackupAgent.this.getClass().getName() + ") threw", ex);

                throw ex;

            } finally {

                // ... and then again after, as in the doBackup() case

                waitForSharedPrefs();



                // Send the EOD marker indicating that there is no more data

                // forthcoming from this agent.

                try {
@@ -624,6 +669,9 @@ public abstract class BackupAgent extends ContextWrapper { 
            } catch (IOException e) {

                throw new RuntimeException(e);

            } finally {

                // Ensure that any side-effect SharedPreferences writes have landed

                waitForSharedPrefs();



                Binder.restoreCallingIdentity(ident);

                try {

                    callbackBinder.opComplete(token);