packagefj;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.Future;
import java.util.concurrent.RecursiveTask;
public class CountTaskextendsRecursiveTask {
       private static final int THRESHOLD= 2;//閾值
       private int start;
       private int end;
       public CountTask(intstart,intend) {
                   this.start= start;
                   this.end= end;
        }
       @Override
       protected Integer compute() {
                   intsum = 0;
                   //如果任務(wù)足夠小就計算任務(wù)
                   booleancanCompute = (end-start) <=THRESHOLD;
                   if(canCompute) {
                              for(inti =start; i <=end; i++) {
                                           sum += i;
                               }
                    }else{
                              //如果任務(wù)大于閥值，就分裂成兩個子任務(wù)計算
                              intmiddle = (start+end) / 2;
                               CountTask leftTask =newCountTask(start, middle);
                               CountTask rightTask =newCountTask(middle + 1,end);
                              //執(zhí)行子任務(wù)
                               leftTask.fork();
                               rightTask.fork();
                              //等待子任務(wù)執(zhí)行完，并得到其結(jié)果
                              intleftResult=leftTask.join();
                              intrightResult=rightTask.join();
                              //合并子任務(wù)
                               sum = leftResult  + rightResult;
                    }
                   returnsum;
        }
       public static void main(String[] args) {
                    ForkJoinPool forkJoinPool =newForkJoinPool();
                   //生成一個計算任務(wù)，負(fù)責(zé)計算1+2+3+4
                    CountTask task =newCountTask(1, 4);
                   //執(zhí)行一個任務(wù)
                    Future result = forkJoinPool.submit(task);
                   try{
                               System.out.println(result.get());
                    }catch(InterruptedException e) {
                    }catch(ExecutionException e) {
                    }
        }
}

if(task.isCompletedAbnormally())
{
System.out.println(task.getException());
}

  public final ForkJoinTask fork() {
          ((ForkJoinWorkerThread) Thread.currentThread())
              .pushTask(this);
          return this;
  }

  final void pushTask(ForkJoinTask t) {
          ForkJoinTask[] q; int s, m;
          if ((q = queue) != null) {    // ignore if queue removed
              long u = (((s = queueTop) & (m = q.length - 1)) << ASHIFT) + ABASE;
              UNSAFE.putOrderedObject(q, u, t);
              queueTop = s + 1;         // or use putOrderedInt
              if ((s -= queueBase) <= 2)
                  pool.signalWork();
      else if (s == m)
                  growQueue();
          }
      }

public final V join() {
          if (doJoin() != NORMAL)
              return reportResult();
          else
              return getRawResult();
  }
  private V reportResult() {
          int s; Throwable ex;
          if ((s = status) == CANCELLED)
              throw new CancellationException();
  if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
              UNSAFE.throwException(ex);
          return getRawResult();
  }

private int doJoin() { 
    Thread t; 
    ForkJoinWorkerThread w;
    int s; 
    booleancompleted; 
    if ((t = Thread.currentThread()) instanceofForkJoinWorkerThread) {
    if ((s = status) < 0) 
    return s; 
    if ((w = (ForkJoinWorkerThread)t).unpushTask(this)) {
        try { 
         completed = exec();
     }
        catch (Throwable rex) { 
            return setExceptionalCompletion(rex); 
        } 
            if (completed) 
            return setCompletion(NORMAL);
            } 
        return w.joinTask(this); 
    } 
           else 
   return externalAwaitDone(); 
   }

//定義一個Task，基礎(chǔ)自RecursiveAction，實(shí)現(xiàn)其compute方法
class SortTask extends RecursiveAction {
    final long[] array;
    final int lo;
    final int hi;
    private int THRESHOLD = 0; //For demo only
    public SortTask(long[] array) {
        this.array = array;
        this.lo = 0;
        this.hi = array.length - 1;
    }
    public SortTask(long[] array, int lo, int hi) {
        this.array = array;
        this.lo = lo;
        this.hi = hi;
    }
    protected void compute() {
        if (hi - lo < THRESHOLD)
            sequentiallySort(array, lo, hi);
        else {
            int pivot = partition(array, lo, hi);  //劃分
            coInvoke(new SortTask(array, lo, pivot - 1), new SortTask(array,
                    pivot + 1, hi));  //遞歸調(diào)，左右2個子數(shù)組
        }
    }
    private int partition(long[] array, int lo, int hi) {
        long x = array[hi];
        int i = lo - 1;
        for (int j = lo; j < hi; j++) {
            if (array[j] <= x) {
                i++;
                swap(array, i, j);
            }
        }
        swap(array, i + 1, hi);
        return i + 1;
    }
    private void swap(long[] array, int i, int j) {
        if (i != j) {
            long temp = array[i];
            array[i] = array[j];
            array[j] = temp;
        }
    }
    private void sequentiallySort(long[] array, int lo, int hi) {
        Arrays.sort(array, lo, hi + 1);
    }
}
//測試函數(shù)
    public void testSort() throws Exception {
        ForkJoinTask sort = new SortTask(array);   //1個任務(wù)
        ForkJoinPool fjpool = new ForkJoinPool();  //1個ForkJoinPool
        fjpool.submit(sort); //提交任務(wù)
        fjpool.shutdown(); //結(jié)束。ForkJoinPool內(nèi)部會開多個線程，并行上面的子任務(wù)
        fjpool.awaitTermination(30, TimeUnit.SECONDS);
    }

//定義一個Task，基礎(chǔ)自RecursiveTask，實(shí)現(xiàn)其commpute方法
public class SumTask extends RecursiveTask<Long>{  
    private static final int THRESHOLD = 10;  
    private long start;  
    private long end;  
    public SumTask(long n) {  
        this(1,n);  
    }  
    private SumTask(long start, long end) {  
        this.start = start;  
        this.end = end;  
    }  
    @Override  //有返回值
    protected Long compute() {  
        long sum = 0;  
        if((end - start) <= THRESHOLD){  
            for(long l = start; l <= end; l++){  
                sum += l;  
            }  
        }else{  
            long mid = (start + end) >>> 1;  
            SumTask left = new SumTask(start, mid);   //分治，遞歸
            SumTask right = new SumTask(mid + 1, end);  
            left.fork();  
            right.fork();  
            sum = left.join() + right.join();  
        }  
        return sum;  
    }  
    private static final long serialVersionUID = 1L;  
}  
//測試函數(shù)
    public void testSum() throws Exception {
        SumTask sum = new SumTask(100);   //1個任務(wù)
        ForkJoinPool fjpool = new ForkJoinPool();  //1個ForkJoinPool
        Future<Long> future = fjpool.submit(sum); //提交任務(wù)
        Long r = future.get(); //獲取返回值
        fjpool.shutdown(); 
    }

//ForkJoinPool的成員變量
ForkJoinWorkerThread[] workers;  //worker thread集合
private ForkJoinTask<?>[] submissionQueue; //外部任務(wù)隊列
private final ReentrantLock submissionLock; 
//ForkJoinWorkerThread的成員變量
ForkJoinTask<?>[] queue;   //每個worker線程自己的內(nèi)部任務(wù)隊列
//提交任務(wù)
public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {  
    if (task == null)  
        throw new NullPointerException();  
    forkOrSubmit(task);  
    return task;  
} 
private <T> void forkOrSubmit(ForkJoinTask<T> task) {  
    ForkJoinWorkerThread w;  
    Thread t = Thread.currentThread();  
    if (shutdown)  
        throw new RejectedExecutionException();  
    if ((t instanceof ForkJoinWorkerThread) &&   //如果當(dāng)前是worker線程提交的任務(wù)，也就是worker執(zhí)行過程中，分裂出來的子任務(wù)，放入worker自己的內(nèi)部任務(wù)隊列
        (w = (ForkJoinWorkerThread)t).pool == this)  
        w.pushTask(task);  
    else  
        addSubmission(task);  //外部任務(wù)，放入pool的全局隊列
}   
//worker的run方法
public void run() {  
    Throwable exception = null;  
    try {  
        onStart();  
        pool.work(this);  
    } catch (Throwable ex) {  
        exception = ex;  
    } finally {  
        onTermination(exception);  
    }  
}  
final void work(ForkJoinWorkerThread w) {  
    boolean swept = false;                // true on empty scans  
    long c;  
    while (!w.terminate && (int)(c = ctl) >= 0) {  
        int a;                            // active count  
        if (!swept && (a = (int)(c >> AC_SHIFT)) <= 0)  
            swept = scan(w, a);   //核心代碼都在這個scan函數(shù)里面
        else if (tryAwaitWork(w, c))  
            swept = false;  
    }  
}  
//scan的基本思路：從別人的任務(wù)隊列里面搶，沒有，再到pool的全局的任務(wù)隊列里面去取。
private boolean scan(ForkJoinWorkerThread w, int a) {  
    int g = scanGuard;   
    int m = (parallelism == 1 - a && blockedCount == 0) ? 0 : g & SMASK;  
    ForkJoinWorkerThread[] ws = workers;  
    if (ws == null || ws.length <= m)         // 過期檢測  
        return false;  
    for (int r = w.seed, k = r, j = -(m + m); j <= m + m; ++j) {  
        ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;  
        //隨機(jī)選出一個犧牲者(工作線程)。  
        ForkJoinWorkerThread v = ws[k & m];  
        //一系列檢查...  
        if (v != null && (b = v.queueBase) != v.queueTop &&  
            (q = v.queue) != null && (i = (q.length - 1) & b) >= 0) {  
            //如果這個犧牲者的任務(wù)隊列中還有任務(wù)，嘗試竊取這個任務(wù)。  
            long u = (i << ASHIFT) + ABASE;  
            if ((t = q[i]) != null && v.queueBase == b &&  
                UNSAFE.compareAndSwapObject(q, u, t, null)) {  
                //竊取成功后，調(diào)整queueBase  
                int d = (v.queueBase = b + 1) - v.queueTop;  
                //將犧牲者的stealHint設(shè)置為當(dāng)前工作線程在pool中的下標(biāo)。  
                v.stealHint = w.poolIndex;  
                if (d != 0)  
                    signalWork();             // 如果犧牲者的任務(wù)隊列還有任務(wù)，繼續(xù)喚醒(或創(chuàng)建)線程。  
                w.execTask(t); //執(zhí)行竊取的任務(wù)。  
            }  
            //計算出下一個隨機(jī)種子。  
            r ^= r << 13; r ^= r >>> 17; w.seed = r ^ (r << 5);  
            return false;                     // 返回false，表示不是一個空掃描。  
        }  
        //前2*m次，隨機(jī)掃描。  
        else if (j < 0) {                     // xorshift  
            r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5;  
        }  
        //后2*m次，順序掃描。  
        else  
            ++k;  
    }  
    if (scanGuard != g)                       // staleness check  
        return false;  
    else {                                     
        //如果掃描完畢后沒找到可竊取的任務(wù)，那么從Pool的提交任務(wù)隊列中取一個任務(wù)來執(zhí)行。  
        ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;  
        if ((b = queueBase) != queueTop &&  
            (q = submissionQueue) != null &&  
            (i = (q.length - 1) & b) >= 0) {  
            long u = (i << ASHIFT) + ABASE;  
            if ((t = q[i]) != null && queueBase == b &&  
                UNSAFE.compareAndSwapObject(q, u, t, null)) {  
                queueBase = b + 1;  
                w.execTask(t);  
            }  
            return false;  
        }  
        return true;                         // 如果所有的隊列(工作線程的任務(wù)隊列和pool的任務(wù)隊列)都是空的，返回true。  
    }  
}