Issue #89 - LIFO thread pool

Added option to configuration to choose thread pool queue processing
type

UniversalImageLoader/src/com/nostra13/universalimageloader/core/ImageLoader.java

@@ -4,8 +4,11 @@
 import java.util.Collections;
 import java.util.Map;
 import java.util.WeakHashMap;
+import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.ExecutorService;
-import java.util.concurrent.Executors;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
 import java.util.concurrent.locks.ReentrantLock;
 
 import android.content.Context;
@@ -23,6 +26,8 @@
 import com.nostra13.universalimageloader.core.assist.ImageSize;
 import com.nostra13.universalimageloader.core.assist.MemoryCacheKeyUtil;
 import com.nostra13.universalimageloader.core.assist.SimpleImageLoadingListener;
+import com.nostra13.universalimageloader.core.assist.QueueProcessingType;
+import com.nostra13.universalimageloader.core.assist.deque.LIFOLinkedBlockingDeque;
 import com.nostra13.universalimageloader.core.display.BitmapDisplayer;
 import com.nostra13.universalimageloader.core.display.FakeBitmapDisplayer;
 
@@ -211,7 +216,7 @@ public void displayImage(String uri, ImageView imageView, DisplayImageOptions op
 				}
 			}
 
-			checkExecutors();
+			initExecutorsIfNeed();
 			ImageLoadingInfo imageLoadingInfo = new ImageLoadingInfo(uri, imageView, targetSize, options, listener, getLockForUri(uri));
 			LoadAndDisplayImageTask displayImageTask = new LoadAndDisplayImageTask(configuration, imageLoadingInfo, new Handler());
 			boolean isImageCachedOnDisc = configuration.discCache.get(uri).exists();
@@ -339,15 +344,22 @@ public void loadImage(Context context, String uri, ImageSize minImageSize, Displ
 		displayImage(uri, fakeImage, optionsWithFakeDisplayer, listener);
 	}
 
-	private void checkExecutors() {
+	private void initExecutorsIfNeed() {
 		if (imageLoadingExecutor == null || imageLoadingExecutor.isShutdown()) {
-			imageLoadingExecutor = Executors.newFixedThreadPool(configuration.threadPoolSize, configuration.displayImageThreadFactory);
+			imageLoadingExecutor = createExecutor();
 		}
 		if (cachedImageLoadingExecutor == null || cachedImageLoadingExecutor.isShutdown()) {
-			cachedImageLoadingExecutor = Executors.newFixedThreadPool(configuration.threadPoolSize, configuration.displayImageThreadFactory);
+			cachedImageLoadingExecutor = createExecutor();
 		}
 	}
 
+	private ExecutorService createExecutor() {
+		boolean lifo = configuration.tasksProcessingType == QueueProcessingType.LIFO;
+		BlockingQueue<Runnable> taskQueue = lifo ? new LIFOLinkedBlockingDeque<Runnable>() : new LinkedBlockingQueue<Runnable>();
+		return new ThreadPoolExecutor(configuration.threadPoolSize, configuration.threadPoolSize, 0L, TimeUnit.MILLISECONDS, taskQueue,
+				configuration.displayImageThreadFactory);
+	}
+
 	/** Returns memory cache */
 	public MemoryCacheAware<String, Bitmap> getMemoryCache() {
 		return configuration.memoryCache;

UniversalImageLoader/src/com/nostra13/universalimageloader/core/ImageLoaderConfiguration.java

@@ -14,6 +14,7 @@
 import com.nostra13.universalimageloader.cache.memory.MemoryCacheAware;
 import com.nostra13.universalimageloader.core.assist.FailReason;
 import com.nostra13.universalimageloader.core.assist.ImageLoadingListener;
+import com.nostra13.universalimageloader.core.assist.QueueProcessingType;
 import com.nostra13.universalimageloader.core.download.ImageDownloader;
 
 /**
@@ -35,14 +36,17 @@ public final class ImageLoaderConfiguration {
 	final int maxImageHeightForDiscCache;
 	final CompressFormat imageCompressFormatForDiscCache;
 	final int imageQualityForDiscCache;
+
 	final int threadPoolSize;
 	final boolean handleOutOfMemory;
+	final QueueProcessingType tasksProcessingType;
+
 	final MemoryCacheAware<String, Bitmap> memoryCache;
 	final DiscCacheAware discCache;
+	final ImageDownloader downloader;
 	final DisplayImageOptions defaultDisplayImageOptions;
 	final ThreadFactory displayImageThreadFactory;
 	final boolean loggingEnabled;
-	final ImageDownloader downloader;
 
 	private ImageLoaderConfiguration(final Builder builder) {
 		maxImageWidthForMemoryCache = builder.maxImageWidthForMemoryCache;
@@ -58,6 +62,7 @@ private ImageLoaderConfiguration(final Builder builder) {
 		defaultDisplayImageOptions = builder.defaultDisplayImageOptions;
 		loggingEnabled = builder.loggingEnabled;
 		downloader = builder.downloader;
+		tasksProcessingType = builder.tasksProcessingType;
 		displayImageThreadFactory = new ThreadFactory() {
 			@Override
 			public Thread newThread(Runnable r) {
@@ -85,6 +90,7 @@ public Thread newThread(Runnable r) {
 	 * <li>imageDownloader = {@link ImageDownloader#createDefault()}</li>
 	 * <li>discCacheFileNameGenerator = {@link FileNameGenerator#createDefault()}</li>
 	 * <li>defaultDisplayImageOptions = {@link DisplayImageOptions#createSimple() Simple options}</li>
+	 * <li>tasksProcessingOrder = {@link QueueProcessingType#FIFO}</li>
 	 * <li>detailed logging disabled</li>
 	 * </ul>
 	 * */
@@ -126,6 +132,7 @@ public static class Builder {
 		private int threadPriority = DEFAULT_THREAD_PRIORITY;
 		private boolean denyCacheImageMultipleSizesInMemory = false;
 		private boolean handleOutOfMemory = true;
+		private QueueProcessingType tasksProcessingType = QueueProcessingType.FIFO;
 
 		private int memoryCacheSize = DEFAULT_MEMORY_CACHE_SIZE;
 		private int discCacheSize = 0;
@@ -233,6 +240,15 @@ public Builder offOutOfMemoryHandling() {
 			return this;
 		}
 
+		/**
+		 * Sets type of queue processing for tasks for loading and displaying images.<br />
+		 * Default value - {@link QueueProcessingType#FIFO}
+		 */
+		public Builder tasksProcessingOrder(QueueProcessingType tasksProcessingType) {
+			this.tasksProcessingType = tasksProcessingType;
+			return this;
+		}
+
 		/**
 		 * Sets maximum memory cache size for {@link android.graphics.Bitmap bitmaps} (in bytes).<br />
 		 * Default value - {@link #DEFAULT_MEMORY_CACHE_SIZE this}<br />

UniversalImageLoader/src/com/nostra13/universalimageloader/core/assist/QueueProcessingType.java

@@ -0,0 +1,10 @@
+package com.nostra13.universalimageloader.core.assist;
+
+/**
+ * Queue processing type which will be used for display task processing
+ * 
+ * @author Sergey Tarasevich (nostra13[at]gmail[dot]com)
+ */
+public enum QueueProcessingType {
+	FIFO, LIFO
+}