在Java中指定任務訂單執行

Question

我已經搜索了很多，但找不到任何解決方案。 我用java線程池以這樣的方式：

ExecutorService c = Executors.newFixedThreadPool(3); 
for (int i = 0; i < 10; ++i) { 
    c.execute(new MyTask(i)); 
} 

在這種方式中的任務隨後順序執行（如在隊列）。但我需要改變「選擇下一個任務」的策略。所以我想分配給每個任務指定優先級（它不是線程優先級）並且執行任務對應於這些優先級。所以當執行者完成另一個任務時，它選擇下一個任務作爲具有最高優先級的任務。 它描述了常見的問題。也許有更簡單的方法不考慮優先事項。它選擇最後添加的任務作爲下一個執行而不是第一次添加。大致來說FixedThreadPool使用FIFO策略。我可以使用例如LIFO策略嗎？

Answer 1

您想創建一個LIFO執行程序嗎？ 希望這個線程可以幫助你

How to create LIFO executor

Answer 2

您可以使用PriorityBlockingQueue指定隊列來的ThreadPoolExecutor。

public class PriorityExecutor extends ThreadPoolExecutor { 

    public PriorityExecutor(int corePoolSize, int maximumPoolSize, 
      long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) { 
     super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue); 
    } 
    //Utitlity method to create thread pool easily 
    public static ExecutorService newFixedThreadPool(int nThreads) { 
     return new PriorityExecutor(nThreads, nThreads, 0L, 
       TimeUnit.MILLISECONDS, new PriorityBlockingQueue<Runnable>()); 
    } 
    //Submit with New comparable task 
    public Future<?> submit(Runnable task, int priority) { 
     return super.submit(new ComparableFutureTask(task, null, priority)); 
    } 
    //execute with New comparable task 
    public void execute(Runnable command, int priority) { 
     super.execute(new ComparableFutureTask(command, null, priority)); 
    } 
} 

定義ComparableFutureTask比較優先級。

class ComparableFutureTask<T> extends FutureTask<T> 
     implements 
      Comparable<ComparableFutureTask<T>> { 

    volatile int priority = 0; 

    public ComparableFutureTask(Runnable runnable, T result, int priority) { 
     super(runnable, result); 
     this.priority = priority; 
    } 
    public ComparableFutureTask(Callable<T> callable, int priority) { 
     super(callable); 
     this.priority = priority; 
    } 
    @Override 
    public int compareTo(ComparableFutureTask<T> o) { 
     return Integer.valueOf(priority).compareTo(o.priority); 
    } 
    } 

Answer 3

ThreadPoolExecutor構造函數接受BlockingQueue。 您可以將隊列作爲PriorityBlockingQueue傳遞。它不會讓任何受權人訂購您需要通過自定義比較器來維護訂單。

static BlockingQueue<Task> queue=new PriorityBlockingQueue<Task>(MAXPOOL,new TaskComparator()); 

static ThreadPoolExecutor threadpool = new ThreadPoolExecutor(30, MAXPOOL, 
     MAXPOOL, TimeUnit.SECONDS, (PriorityBlockingQueue) queue, new mThreadFactory()); 



class TaskComparator implements Comparator<Task>{ 
    public int compare(Task t1, Task t2){ 
    //write you own logic to compare two task. 
    } 
}