Android開源架構：Universal-Image-Loader解析（四）TaskProcess

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Universal-Image-Loader中，對Task的處理有兩種方法：FIFO，LIFO

在core/assist下的deque包中，其主要是定義了LIFOLinkedBlockingDeque，其他的幾個均在java.util和java.util.concurr中

下面我們對queue和deque及其相關的類擼一擼，看看它們的區別

1. Queue：隊列， 繼承於Collection，定義了幾個與隊列相關的方法

2. Deque：雙向隊列，繼承於Queue，定義了和雙向操作相關的方法

3. BlockingQueue：阻塞隊列

4. BlockingDeque：雙向阻塞隊列

5. AbstractQueue： 實現了隊列的幾個基本方法，

6. LinkedBlockingQueue：安全執行緒，阻塞隊列，預設長度是Integer.MAX_VALUE

    按 FIFO（先進先出）排序元素。隊列的頭部 是在隊列中時間最長的元素。隊列的尾部 是在隊列中時間最短的元素。 連結隊列的輸送量通常要高於基於數組的隊列。

 1 /** 2      * Linked list node class，單向的列表 3      */ 4     static class Node<E> { 5         E item; 6         /** 7          * One of: 8          * - the real successor Node 9          * - this Node, meaning the successor is head.next10          * - null, meaning there is no successor (this is the last node)11          */12 13         Node<E> next;14         Node(E x) { item = x; }15     }

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7. LinkedBlockingDeque：安全執行緒，雙向阻塞隊列，其實現主要是基於兩個Node，預設長度是Integer.MAX_VALUE

 1 /** Doubly-linked list node class 雙向鏈表*/ 2     static final class Node<E> { 3         /** 4          * The item, or null if this node has been removed. 5          */ 6         E item; 7  8         /** 9          * One of:10          * - the real predecessor Node11          * - this Node, meaning the predecessor is tail12          * - null, meaning there is no predecessor13          */14         Node<E> prev;15 16         /**17          * One of:18          * - the real successor Node19          * - this Node, meaning the successor is head20          * - null, meaning there is no successor21          */22         Node<E> next;23 24         Node(E x) {25             item = x;26         }27     }28 29     /**30      * Pointer to first node.前端節點31      * Invariant: (first == null && last == null) ||32      *            (first.prev == null && first.item != null)33      */34     transient Node<E> first;35 36     /**37      * Pointer to last node.尾節點38      * Invariant: (first == null && last == null) ||39      *            (last.next == null && last.item != null)40      */41     transient Node<E> last;

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8. LIFOLinkedBlockingDeque：後進先出，雙向阻塞隊列，僅僅override兩個方法

 1 @Override 2     public boolean offer(T e) { 3         return super.offerFirst(e); 4     } 5  6     /** 7      * Retrieves and removes the first element of this deque. This method differs from {@link #pollFirst pollFirst} only 8      * in that it throws an exception if this deque is empty. 9      * 10      * @return the head of this deque11      * @throws NoSuchElementException12      *             if this deque is empty13      */14     @Override15     public T remove() {16         return super.removeFirst();17     }

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阻塞隊列的工作原理：一個線程（生產者）放入任務，另外一個線程（消費者）取出任務

參考連結：http://www.cnblogs.com/qiengo/archive/2012/12/19/2824971.html

Android開源架構：Universal-Image-Loader解析（四）TaskProcess