Marcel Offermans | 89a8a6b | 2007-06-08 21:27:59 +0000 | [diff] [blame^] | 1 | package org.apache.felix.dependencymanager; |
| 2 | |
| 3 | import java.util.LinkedList; |
| 4 | import java.util.NoSuchElementException; |
| 5 | |
| 6 | /** |
| 7 | * Allows you to enqueue tasks from multiple threads and then execute |
| 8 | * them on one thread sequentially. It assumes more than one thread will |
| 9 | * try to execute the tasks and it will make an effort to pick the first |
| 10 | * task that comes along whilst making sure subsequent tasks return |
| 11 | * without waiting. |
| 12 | * |
| 13 | * @author <a href="mailto:dev@felix.apache.org">Felix Project Team</a> |
| 14 | */ |
| 15 | public final class SerialExecutor { |
| 16 | private final LinkedList m_workQueue = new LinkedList(); |
| 17 | private Runnable m_active; |
| 18 | |
| 19 | /** |
| 20 | * Enqueue a new task for later execution. This method is |
| 21 | * thread-safe, so multiple threads can contribute tasks. |
| 22 | * |
| 23 | * @param runnable the runnable containing the actual task |
| 24 | */ |
| 25 | public synchronized void enqueue(final Runnable runnable) { |
| 26 | m_workQueue.addLast(new Runnable() { |
| 27 | public void run() { |
| 28 | try { |
| 29 | runnable.run(); |
| 30 | } |
| 31 | finally { |
| 32 | scheduleNext(); |
| 33 | } |
| 34 | } |
| 35 | }); |
| 36 | } |
| 37 | |
| 38 | /** |
| 39 | * Execute any pending tasks. This method is thread safe, |
| 40 | * so multiple threads can try to execute the pending |
| 41 | * tasks, but only the first will be used to actually do |
| 42 | * so. Other threads will return immediately. |
| 43 | */ |
| 44 | public void execute() { |
| 45 | Runnable active; |
| 46 | synchronized (this) { |
| 47 | active = m_active; |
| 48 | } |
| 49 | if (active == null) { |
| 50 | scheduleNext(); |
| 51 | } |
| 52 | } |
| 53 | |
| 54 | private void scheduleNext() { |
| 55 | Runnable active; |
| 56 | synchronized (this) { |
| 57 | try { |
| 58 | m_active = (Runnable) m_workQueue.removeFirst(); |
| 59 | } |
| 60 | catch (NoSuchElementException e) { |
| 61 | m_active = null; |
| 62 | } |
| 63 | active = m_active; |
| 64 | } |
| 65 | if (active != null) { |
| 66 | active.run(); |
| 67 | } |
| 68 | } |
| 69 | |
| 70 | /* |
| 71 | class SerialExecutor implements Executor { |
| 72 | final Queue<Runnable> tasks = new LinkedBlockingQueue<Runnable>(); |
| 73 | final Executor executor; |
| 74 | Runnable active; |
| 75 | |
| 76 | SerialExecutor(Executor executor) { |
| 77 | this.executor = executor; |
| 78 | } |
| 79 | |
| 80 | public synchronized void execute(final Runnable r) { |
| 81 | tasks.offer(new Runnable() { |
| 82 | public void run() { |
| 83 | try { |
| 84 | r.run(); |
| 85 | } finally { |
| 86 | scheduleNext(); |
| 87 | } |
| 88 | } |
| 89 | }); |
| 90 | if (active == null) { |
| 91 | scheduleNext(); |
| 92 | } |
| 93 | } |
| 94 | |
| 95 | protected synchronized void scheduleNext() { |
| 96 | if ((active = tasks.poll()) != null) { |
| 97 | executor.execute(active); |
| 98 | } |
| 99 | } |
| 100 | } |
| 101 | */ |
| 102 | |
| 103 | |
| 104 | // just some test code ;) |
| 105 | public static void main(String[] args) { |
| 106 | final SerialExecutor se = new SerialExecutor(); |
| 107 | (new Thread("T1") { public void run() { |
| 108 | for (int i = 0; i < 100; i++) { |
| 109 | final int nr = i; |
| 110 | se.enqueue(new Runnable() { public void run() { |
| 111 | System.out.println("A" + nr + ":" + Thread.currentThread().getName()); |
| 112 | if (nr % 10 == 5) { |
| 113 | try { Thread.sleep(10); } catch (InterruptedException ie) {} |
| 114 | } |
| 115 | }}); |
| 116 | try { Thread.sleep(1); } catch (InterruptedException ie) {} |
| 117 | se.execute(); |
| 118 | } |
| 119 | System.out.println("A is done"); |
| 120 | }}).start(); |
| 121 | try { Thread.sleep(5); } catch (InterruptedException ie) {} |
| 122 | (new Thread("T2") { public void run() { |
| 123 | for (int i = 0; i < 100; i++) { |
| 124 | final int nr = i; |
| 125 | se.enqueue(new Runnable() { public void run() { |
| 126 | System.out.println("B" + nr + ":" + Thread.currentThread().getName()); |
| 127 | if (nr % 19 == 6) { |
| 128 | try { Thread.sleep(20); } catch (InterruptedException ie) {} |
| 129 | } |
| 130 | }}); |
| 131 | try { Thread.sleep(1); } catch (InterruptedException ie) {} |
| 132 | se.execute(); |
| 133 | } |
| 134 | System.out.println("B is done"); |
| 135 | }}).start(); |
| 136 | try { Thread.sleep(5); } catch (InterruptedException ie) {} |
| 137 | (new Thread("T3") { public void run() { |
| 138 | for (int i = 0; i < 100; i++) { |
| 139 | final int nr = i; |
| 140 | se.enqueue(new Runnable() { public void run() { |
| 141 | System.out.println("C" + nr + ":" + Thread.currentThread().getName()); |
| 142 | }}); |
| 143 | se.execute(); |
| 144 | } |
| 145 | System.out.println("C is done"); |
| 146 | }}).start(); |
| 147 | } |
| 148 | } |