| 1 | package dk.deepthought.sidious.util; |
| 2 | |
| 3 | import java.util.LinkedList; |
| 4 | import java.util.List; |
| 5 | |
| 6 | import net.jcip.annotations.ThreadSafe; |
| 7 | |
| 8 | import org.apache.commons.logging.Log; |
| 9 | import org.apache.commons.logging.LogFactory; |
| 10 | |
| 11 | /** |
| 12 | * Abstract representation of a queue which uses a thread to dequeue and process |
| 13 | * elements. |
| 14 | * <p> |
| 15 | * Implements a work queue; which allows for asynchronous processing of enqueued |
| 16 | * items. |
| 17 | * |
| 18 | * @author Deepthought |
| 19 | * |
| 20 | */ |
| 21 | @ThreadSafe |
| 22 | public abstract class SidiousQueue<T> { |
| 23 | /** |
| 24 | * Logger for this class |
| 25 | */ |
| 26 | private static final Log logger = LogFactory.getLog(SidiousQueue.class); |
| 27 | |
| 28 | /** |
| 29 | * Private thread implementation. |
| 30 | */ |
| 31 | private class InternalThread implements Runnable { |
| 32 | public void run() { |
| 33 | if (logger.isDebugEnabled()) { |
| 34 | logger.debug("run() - start"); |
| 35 | } |
| 36 | |
| 37 | while (true) { |
| 38 | T item = null; |
| 39 | synchronized (queue) { |
| 40 | while (queue.isEmpty() && !interrupted) { |
| 41 | try { |
| 42 | if (logger.isDebugEnabled()) { |
| 43 | logger.debug("run() - waiting - start"); |
| 44 | } |
| 45 | queue.wait(); |
| 46 | if (logger.isDebugEnabled()) { |
| 47 | logger.debug("run() - waiting - end"); |
| 48 | } |
| 49 | } catch (InterruptedException e) { |
| 50 | logger.error("run()", e); |
| 51 | return; |
| 52 | } |
| 53 | } |
| 54 | if (interrupted) { |
| 55 | if (logger.isDebugEnabled()) { |
| 56 | logger.debug("run() - interrupted"); |
| 57 | } |
| 58 | |
| 59 | return; |
| 60 | } |
| 61 | item = queue.remove(0); |
| 62 | if (logger.isDebugEnabled()) { |
| 63 | logger.debug("run() - " + item + " dequeued"); |
| 64 | } |
| 65 | } |
| 66 | process(item); |
| 67 | } |
| 68 | } |
| 69 | } |
| 70 | |
| 71 | /** |
| 72 | * Boolean to indicate whether the thread has been interrupted. |
| 73 | */ |
| 74 | private boolean interrupted = false; |
| 75 | |
| 76 | /** |
| 77 | * Internal queue. |
| 78 | */ |
| 79 | private final List<T> queue = new LinkedList<T>(); |
| 80 | |
| 81 | /** |
| 82 | * Constructor that starts a new thread. |
| 83 | */ |
| 84 | protected SidiousQueue(String name) { |
| 85 | startThread(name); |
| 86 | } |
| 87 | |
| 88 | /** |
| 89 | * Enqueues an item. |
| 90 | * |
| 91 | * @param item |
| 92 | * the item to be enqueued |
| 93 | */ |
| 94 | public final void enqueue(T item) { |
| 95 | if (logger.isDebugEnabled()) { |
| 96 | logger.debug("enqueue(item=" + item + ") - start"); |
| 97 | } |
| 98 | synchronized (queue) { |
| 99 | queue.add(item); |
| 100 | queue.notify(); |
| 101 | } |
| 102 | |
| 103 | if (logger.isDebugEnabled()) { |
| 104 | logger.debug("enqueue(item=" + item + ") - end"); |
| 105 | } |
| 106 | } |
| 107 | |
| 108 | /** |
| 109 | * Interrupts the thread. |
| 110 | */ |
| 111 | public final void interrupt() { |
| 112 | if (logger.isDebugEnabled()) { |
| 113 | logger.debug("interrupt() - start"); |
| 114 | } |
| 115 | synchronized (queue) { |
| 116 | interrupted = true; |
| 117 | queue.notify(); |
| 118 | } |
| 119 | if (logger.isDebugEnabled()) { |
| 120 | logger.debug("interrupt() - end"); |
| 121 | } |
| 122 | } |
| 123 | |
| 124 | /** |
| 125 | * The processing of an item. |
| 126 | * |
| 127 | * @param item |
| 128 | * the item to be processed. |
| 129 | */ |
| 130 | protected abstract void process(T item); |
| 131 | |
| 132 | /** |
| 133 | * Method to start the thread. |
| 134 | * |
| 135 | * @param name |
| 136 | * the name of the thread |
| 137 | */ |
| 138 | private void startThread(String name) { |
| 139 | Thread thread = new Thread(new InternalThread(), name); |
| 140 | thread.setDaemon(false); |
| 141 | thread.start(); |
| 142 | if (logger.isDebugEnabled()) { |
| 143 | logger.debug("startThread() - Thread started"); |
| 144 | } |
| 145 | } |
| 146 | |
| 147 | } |