src/com/android/photos/data/SQLiteContentProvider.java

/*
 * Copyright (C) 2013 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 com.android.photos.data;

import android.content.ContentProvider;
import android.content.ContentProviderOperation;
import android.content.ContentProviderResult;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.content.Context;
import android.content.OperationApplicationException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.net.Uri;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Set;

/**
 * General purpose {@link ContentProvider} base class that uses SQLiteDatabase
 * for storage.
 */
public abstract class SQLiteContentProvider extends ContentProvider {

    @SuppressWarnings("unused")
    private static final String TAG = "SQLiteContentProvider";

    private SQLiteOpenHelper mOpenHelper;
    private Set<Uri> mChangedUris;

    private final ThreadLocal<Boolean> mApplyingBatch = new ThreadLocal<Boolean>();
    private static final int SLEEP_AFTER_YIELD_DELAY = 4000;

    /**
     * Maximum number of operations allowed in a batch between yield points.
     */
    private static final int MAX_OPERATIONS_PER_YIELD_POINT = 500;

    @Override
    public boolean onCreate() {
        Context context = getContext();
        mOpenHelper = getDatabaseHelper(context);
        mChangedUris = new HashSet<Uri>();
        return true;
    }

    @Override
    public void shutdown() {
        getDatabaseHelper().close();
    }

    /**
     * Returns a {@link SQLiteOpenHelper} that can open the database.
     */
    public abstract SQLiteOpenHelper getDatabaseHelper(Context context);

    /**
     * The equivalent of the {@link #insert} method, but invoked within a
     * transaction.
     */
    public abstract Uri insertInTransaction(Uri uri, ContentValues values,
            boolean callerIsSyncAdapter);

    /**
     * The equivalent of the {@link #update} method, but invoked within a
     * transaction.
     */
    public abstract int updateInTransaction(Uri uri, ContentValues values, String selection,
            String[] selectionArgs, boolean callerIsSyncAdapter);

    /**
     * The equivalent of the {@link #delete} method, but invoked within a
     * transaction.
     */
    public abstract int deleteInTransaction(Uri uri, String selection, String[] selectionArgs,
            boolean callerIsSyncAdapter);

    /**
     * Call this to add a URI to the list of URIs to be notified when the
     * transaction is committed.
     */
    protected void postNotifyUri(Uri uri) {
        synchronized (mChangedUris) {
            mChangedUris.add(uri);
        }
    }

    public boolean isCallerSyncAdapter(Uri uri) {
        return false;
    }

    public SQLiteOpenHelper getDatabaseHelper() {
        return mOpenHelper;
    }

    private boolean applyingBatch() {
        return mApplyingBatch.get() != null && mApplyingBatch.get();
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        Uri result = null;
        boolean callerIsSyncAdapter = isCallerSyncAdapter(uri);
        boolean applyingBatch = applyingBatch();
        if (!applyingBatch) {
            SQLiteDatabase db = mOpenHelper.getWritableDatabase();
            db.beginTransaction();
            try {
                result = insertInTransaction(uri, values, callerIsSyncAdapter);
                db.setTransactionSuccessful();
            } finally {
                db.endTransaction();
            }

            onEndTransaction(callerIsSyncAdapter);
        } else {
            result = insertInTransaction(uri, values, callerIsSyncAdapter);
        }
        return result;
    }

    @Override
    public int bulkInsert(Uri uri, ContentValues[] values) {
        int numValues = values.length;
        boolean callerIsSyncAdapter = isCallerSyncAdapter(uri);
        SQLiteDatabase db = mOpenHelper.getWritableDatabase();
        db.beginTransaction();
        try {
            for (int i = 0; i < numValues; i++) {
                @SuppressWarnings("unused")
                Uri result = insertInTransaction(uri, values[i], callerIsSyncAdapter);
                db.yieldIfContendedSafely();
            }
            db.setTransactionSuccessful();
        } finally {
            db.endTransaction();
        }

        onEndTransaction(callerIsSyncAdapter);
        return numValues;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
        int count = 0;
        boolean callerIsSyncAdapter = isCallerSyncAdapter(uri);
        boolean applyingBatch = applyingBatch();
        if (!applyingBatch) {
            SQLiteDatabase db = mOpenHelper.getWritableDatabase();
            db.beginTransaction();
            try {
                count = updateInTransaction(uri, values, selection, selectionArgs,
                        callerIsSyncAdapter);
                db.setTransactionSuccessful();
            } finally {
                db.endTransaction();
            }

            onEndTransaction(callerIsSyncAdapter);
        } else {
            count = updateInTransaction(uri, values, selection, selectionArgs, callerIsSyncAdapter);
        }

        return count;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        int count = 0;
        boolean callerIsSyncAdapter = isCallerSyncAdapter(uri);
        boolean applyingBatch = applyingBatch();
        if (!applyingBatch) {
            SQLiteDatabase db = mOpenHelper.getWritableDatabase();
            db.beginTransaction();
            try {
                count = deleteInTransaction(uri, selection, selectionArgs, callerIsSyncAdapter);
                db.setTransactionSuccessful();
            } finally {
                db.endTransaction();
            }

            onEndTransaction(callerIsSyncAdapter);
        } else {
            count = deleteInTransaction(uri, selection, selectionArgs, callerIsSyncAdapter);
        }
        return count;
    }

    @Override
    public ContentProviderResult[] applyBatch(ArrayList<ContentProviderOperation> operations)
            throws OperationApplicationException {
        int ypCount = 0;
        int opCount = 0;
        boolean callerIsSyncAdapter = false;
        SQLiteDatabase db = mOpenHelper.getWritableDatabase();
        db.beginTransaction();
        try {
            mApplyingBatch.set(true);
            final int numOperations = operations.size();
            final ContentProviderResult[] results = new ContentProviderResult[numOperations];
            for (int i = 0; i < numOperations; i++) {
                if (++opCount >= MAX_OPERATIONS_PER_YIELD_POINT) {
                    throw new OperationApplicationException(
                            "Too many content provider operations between yield points. "
                                    + "The maximum number of operations per yield point is "
                                    + MAX_OPERATIONS_PER_YIELD_POINT, ypCount);
                }
                final ContentProviderOperation operation = operations.get(i);
                if (!callerIsSyncAdapter && isCallerSyncAdapter(operation.getUri())) {
                    callerIsSyncAdapter = true;
                }
                if (i > 0 && operation.isYieldAllowed()) {
                    opCount = 0;
                    if (db.yieldIfContendedSafely(SLEEP_AFTER_YIELD_DELAY)) {
                        ypCount++;
                    }
                }
                results[i] = operation.apply(this, results, i);
            }
            db.setTransactionSuccessful();
            return results;
        } finally {
            mApplyingBatch.set(false);
            db.endTransaction();
            onEndTransaction(callerIsSyncAdapter);
        }
    }

    protected Set<Uri> onEndTransaction(boolean callerIsSyncAdapter) {
        Set<Uri> changed;
        synchronized (mChangedUris) {
            changed = new HashSet<Uri>(mChangedUris);
            mChangedUris.clear();
        }
        ContentResolver resolver = getContext().getContentResolver();
        for (Uri uri : changed) {
            boolean syncToNetwork = !callerIsSyncAdapter && syncToNetwork(uri);
            notifyChange(resolver, uri, syncToNetwork);
        }
        return changed;
    }

    protected void notifyChange(ContentResolver resolver, Uri uri, boolean syncToNetwork) {
        resolver.notifyChange(uri, null, syncToNetwork);
    }

    protected boolean syncToNetwork(Uri uri) {
        return false;
    }
}