Stuart McCulloch | 26e7a5a | 2011-10-17 10:31:43 +0000 | [diff] [blame^] | 1 | package aQute.libg.forker; |
| 2 | |
| 3 | import java.util.*; |
| 4 | import java.util.concurrent.*; |
| 5 | import java.util.concurrent.atomic.*; |
| 6 | |
| 7 | /** |
| 8 | * A Forker is good in parallel scheduling tasks with dependencies. You can add |
| 9 | * tasks with {@link #doWhen(Collection, Object, Runnable)}. The collection is |
| 10 | * the list of dependencies, the object is the target, and the runnable is run |
| 11 | * to update the target. The runnable will only run when all its dependencies |
| 12 | * have ran their associated runnable. |
| 13 | * |
| 14 | * @author aqute |
| 15 | * |
| 16 | * @param <T> |
| 17 | */ |
| 18 | public class Forker<T> { |
| 19 | final Executor executor; |
| 20 | final Set<T> done = new HashSet<T>(); |
| 21 | final List<Job> waiting = new ArrayList<Job>(); |
| 22 | final Semaphore semaphore = new Semaphore(0); |
| 23 | final AtomicInteger outstanding = new AtomicInteger(); |
| 24 | final AtomicBoolean canceled = new AtomicBoolean(); |
| 25 | |
| 26 | /** |
| 27 | * Helper class to model a Job |
| 28 | */ |
| 29 | class Job implements Runnable { |
| 30 | T target; |
| 31 | Set<T> dependencies; |
| 32 | Runnable runnable; |
| 33 | Throwable exception; |
| 34 | volatile Thread t; |
| 35 | volatile AtomicBoolean canceled = new AtomicBoolean(false); |
| 36 | |
| 37 | /** |
| 38 | * Run when the job's dependencies are done. |
| 39 | */ |
| 40 | public void run() { |
| 41 | Thread.interrupted(); // clear the interrupt flag |
| 42 | |
| 43 | try { |
| 44 | synchronized (this) { |
| 45 | // Check if we got canceled |
| 46 | if (canceled.get()) |
| 47 | return; |
| 48 | |
| 49 | t = Thread.currentThread(); |
| 50 | } |
| 51 | runnable.run(); |
| 52 | } catch (Exception e) { |
| 53 | exception = e; |
| 54 | } finally { |
| 55 | synchronized (this) { |
| 56 | t = null; |
| 57 | } |
| 58 | Thread.interrupted(); // clear the interrupt flag |
| 59 | done(target); |
| 60 | } |
| 61 | } |
| 62 | |
| 63 | /** |
| 64 | * Cancel this job |
| 65 | */ |
| 66 | private void cancel() { |
| 67 | if (!canceled.getAndSet(true)) { |
| 68 | synchronized (this) { |
| 69 | if (t != null) |
| 70 | t.interrupt(); |
| 71 | } |
| 72 | } |
| 73 | } |
| 74 | } |
| 75 | |
| 76 | /** |
| 77 | * Constructor |
| 78 | * |
| 79 | * @param executor |
| 80 | */ |
| 81 | public Forker(Executor executor) { |
| 82 | this.executor = executor; |
| 83 | } |
| 84 | |
| 85 | /** |
| 86 | * Constructor |
| 87 | * |
| 88 | */ |
| 89 | public Forker() { |
| 90 | this.executor = Executors.newFixedThreadPool(4); |
| 91 | } |
| 92 | |
| 93 | /** |
| 94 | * Schedule a job for execution when the dependencies are done of target are |
| 95 | * done. |
| 96 | * |
| 97 | * @param dependencies the dependencies that must have run |
| 98 | * @param target the target, is removed from all the dependencies when it ran |
| 99 | * @param runnable the runnable to run |
| 100 | */ |
| 101 | public synchronized void doWhen(Collection<? extends T> dependencies, T target, |
| 102 | Runnable runnable) { |
| 103 | System.out.println("doWhen " + dependencies); |
| 104 | outstanding.incrementAndGet(); |
| 105 | Job job = new Job(); |
| 106 | job.dependencies = new HashSet<T>(dependencies); |
| 107 | job.dependencies.removeAll(done); |
| 108 | job.target = target; |
| 109 | |
| 110 | job.runnable = runnable; |
| 111 | if (job.dependencies.isEmpty()) { |
| 112 | executor.execute(job); |
| 113 | } else { |
| 114 | waiting.add(job); |
| 115 | } |
| 116 | } |
| 117 | |
| 118 | /** |
| 119 | * Called when the target has ran by the Job. |
| 120 | * |
| 121 | * @param done |
| 122 | */ |
| 123 | private void done(T done) { |
| 124 | List<Runnable> torun = new ArrayList<Runnable>(); |
| 125 | synchronized (this) { |
| 126 | System.out.println("done " + done); |
| 127 | semaphore.release(); |
| 128 | |
| 129 | for (Iterator<Job> e = waiting.iterator(); e.hasNext();) { |
| 130 | Job job = e.next(); |
| 131 | if (job.dependencies.remove(done) && job.dependencies.isEmpty()) { |
| 132 | System.out.println("scheduling " + job.target); |
| 133 | torun.add(job); |
| 134 | e.remove(); |
| 135 | } |
| 136 | } |
| 137 | } |
| 138 | for (Runnable r : torun) |
| 139 | executor.execute(r); |
| 140 | } |
| 141 | |
| 142 | /** |
| 143 | * Wait until all jobs have run. |
| 144 | * |
| 145 | * @throws InterruptedException |
| 146 | */ |
| 147 | public void join() throws InterruptedException { |
| 148 | System.out.println("join " + outstanding + " " + semaphore); |
| 149 | check(); |
| 150 | semaphore.acquire(outstanding.getAndSet(0)); |
| 151 | } |
| 152 | |
| 153 | /** |
| 154 | * Check that we have no jobs that can never be satisfied. I.e. if |
| 155 | * the dependencies contain a target that is not listed. |
| 156 | */ |
| 157 | private void check() { |
| 158 | // TODO |
| 159 | } |
| 160 | |
| 161 | /** |
| 162 | * Return the number of outstanding jobs |
| 163 | * @return outstanding jobs |
| 164 | */ |
| 165 | public int getOutstanding() { |
| 166 | return semaphore.availablePermits(); |
| 167 | } |
| 168 | |
| 169 | /** |
| 170 | * Cancel the forker. |
| 171 | * |
| 172 | * @throws InterruptedException |
| 173 | */ |
| 174 | public void cancel() throws InterruptedException { |
| 175 | System.out.println("canceled " + outstanding + " " + semaphore); |
| 176 | |
| 177 | if (!canceled.getAndSet(true)) { |
| 178 | for (Job job : waiting) { |
| 179 | job.cancel(); |
| 180 | } |
| 181 | } |
| 182 | join(); |
| 183 | } |
| 184 | } |