ThumbnailCacheWriterTask.java

/*
 * @copyright 2012 Philip Warner
 * @license GNU General Public License
 * 
 * This file is part of Book Catalogue.
 *
 * Book Catalogue is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Book Catalogue is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Book Catalogue.  If not, see <http://www.gnu.org/licenses/>.
 */

package com.eleybourn.bookcatalogue;

import android.graphics.Bitmap;

import com.eleybourn.bookcatalogue.database.CoversDbHelper;
import com.eleybourn.bookcatalogue.utils.SimpleTaskQueue;
import com.eleybourn.bookcatalogue.utils.SimpleTaskQueue.SimpleTask;
import com.eleybourn.bookcatalogue.utils.SimpleTaskQueue.SimpleTaskContext;

/**
 * Background task to save a bitmap into the covers thumbnail database. Runs in background
 * because it involves compression and IO, and can be safely queued. Failures can be ignored
 * because it is just writing to a cache used solely for optimization.
 * 
 * This class also has its onw statis SimpleTaskQueue.
 * 
 * @author Philip Warner
 */
public class ThumbnailCacheWriterTask implements SimpleTask {

	// ******** STATIC Data ******** //
	
	/** 
	 * Single-thread queue for writing data. There is no point in more than one thread since
	 * the database will force serialization of the updates.
	 */
	private static SimpleTaskQueue mQueue = new SimpleTaskQueue("cachewriter", 1);

	/**
	 * Queue the passed bitmap to be compresed and written to the database, will be recycled if
	 * flag is set.
	 * 
	 * @param cacheId		Cache ID to use
	 * @param source		Raw bitmap to store
	 * @param canRecycle	Indicates bitmap should be recycled after use
	 */
	public static void writeToCache(String cacheId, Bitmap source, boolean canRecycle) {
		ThumbnailCacheWriterTask t = new ThumbnailCacheWriterTask(cacheId, source, canRecycle);
		mQueue.enqueue(t);
	}

	/**
	 * Check if there is an active task in the queue.
	 * 
	 * @return
	 */
	public static boolean hasActiveTasks() {
		return mQueue.hasActiveTasks();
	}

	// ******** INSTANCE Data ******** //

	/** Cache ID of this object */
	private String mCacheId;
	/** Indicates if Bitmap can be recycled when no longer needed */
	private final boolean mCanRecycle;
	/** Bitmap to store */
	private Bitmap mBitmap;

	/**
	 * Create a task that will compress the passed bitmap and write it to the database, 
	 * it will also be recycled if flag is set.
	 * 
	 * @param cacheId		Cache ID to use
	 * @param source		Raw bitmap to store
	 * @param canRecycle	Indicates bitmap should be recycled after use
	 */
	public ThumbnailCacheWriterTask(String cacheId, Bitmap source, boolean canRecycle) {
		mCacheId = cacheId;
		mBitmap = source;
		mCanRecycle = canRecycle;
	}

	/**
	 * Do the main work in the background thread.
	 */
	@Override
	public void run(SimpleTaskContext taskContext) {
		if (mBitmap.isRecycled()) {
			// Was probably recycled by rapid scrolling of view
			mBitmap = null;
		} else {
			CoversDbHelper db = null;
			try {
				db = taskContext.getCoversDb();
			} catch (Exception e) {
				// No db...
			}
			if (db != null)
				db.saveFile(mCacheId, mBitmap);
			if (mCanRecycle) {
				mBitmap.recycle();
				mBitmap = null;
			}
		}
		mCacheId = null;
	}

	@Override
	public void onFinish(Exception e) {
	}

}