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本篇內(nèi)容主要講解“自定義FutureTask的實(shí)現(xiàn)方法”,感興趣的朋友不妨來看看。本文介紹的方法操作簡單快捷,實(shí)用性強(qiáng)。下面就讓小編來帶大家學(xué)習(xí)“自定義FutureTask的實(shí)現(xiàn)方法”吧!
FutureTask是Future的實(shí)現(xiàn),用來異步任務(wù)的獲取結(jié)果,可以啟動和取消異步任務(wù),查詢異步任務(wù)是否計(jì)算結(jié)束以及獲取最終的異步任務(wù)的結(jié)果。通過get()方法來獲取異步任務(wù)的結(jié)果,但是會阻塞當(dāng)前線程直至異步任務(wù)執(zhí)行結(jié)束。一旦任務(wù)執(zhí)行結(jié)束,任務(wù)不能重新啟動或取消,除非調(diào)用runAndReset()方法。
代碼示例:
public class ThreadTest { public static void main(String[] args) throws Exception { Callable<String> myCallable = new MyCallableThread(); FutureTask<String> futureTask = new FutureTask<>(myCallable); Thread myCallableThread = new Thread(futureTask); myCallableThread.setName("MyThread-implements-Callable-test"); myCallableThread.start(); System.out.println("Run by Thread:" + futureTask.get()); //通過線程池執(zhí)行 ExecutorService executorService = Executors.newCachedThreadPool(); executorService.submit(futureTask); executorService.shutdown(); System.out.println("Run by ExecutorService:" + futureTask.get()); } } class MyCallableThread implements Callable<String> { @Override public String call() throws Exception { return Thread.currentThread().getName(); } }
根據(jù)FutureTask核心原理,要實(shí)現(xiàn)一個FutureTask必須滿足以下方面:
需要泛型定義用以返回結(jié)果類型
需要一個callable對象,在構(gòu)造方法中傳入
需要實(shí)現(xiàn)runnable接口,在run方法中實(shí)現(xiàn)具體結(jié)果計(jì)算
需要一個公開的get方法來獲取結(jié)果
如果線程沒有執(zhí)行完,則調(diào)用get方法的線程需要進(jìn)入等待隊(duì)列
需要一個字段記錄線程執(zhí)行的狀態(tài)
需要一個等待隊(duì)列存儲等待結(jié)果的線程
代碼示例:
/** * 1. 泛型定義 * 2. 構(gòu)造方法 callable * 3. 實(shí)現(xiàn)了runnable * 4. get方法返回callable執(zhí)行結(jié)果 * 5. get方法有阻塞的效果(未執(zhí)行結(jié)束的話) */ public class MyFutureTask<T> implements Runnable { // 程序執(zhí)行的結(jié)果 private T result; // 要執(zhí)行的任務(wù) private Callable<T> callable; // 任務(wù)運(yùn)行的狀態(tài) private volatile int state = NEW; // 任務(wù)運(yùn)行的狀態(tài)值 private static final int NEW = 0; private static final int RUNNING = 1; private static final int FINISHED = 2; // 獲取結(jié)果的線程等待隊(duì)列 LinkedBlockingQueue<Thread> waiters = new LinkedBlockingQueue<>(100); // 執(zhí)行當(dāng)前FutureTask的線程,用CAS進(jìn)行爭搶 AtomicReference<Thread> runner = new AtomicReference<>(); public MyFutureTask(Callable<T> task) { this.callable = task; } @Override public void run() { // 判斷當(dāng)前對象的狀態(tài),如果是New且搶鎖成功就執(zhí)行 if (state != NEW || !runner.compareAndSet(null, Thread.currentThread())) return; state = RUNNING; try { result = callable.call(); } catch (Exception e) { e.printStackTrace(); } finally { state = FINISHED; } // 方法執(zhí)行完,喚醒所有線程 while (true) { Thread waiterThread = waiters.poll(); if (waiterThread == null) break; LockSupport.unpark(waiterThread); } } public T get() { // 如果狀態(tài)不是FINISHED,則進(jìn)入等待隊(duì)列 if (state != FINISHED) { waiters.offer(Thread.currentThread()); } while (state != FINISHED) { LockSupport.park(); } return result; } } // MyFutureTask 測試 public class FutureTaskTest { public static void main(String[] args) { Callable<String> myCallable = new MyCallableThread(); MyFutureTask<String> futureTask = new MyFutureTask<>(myCallable); Thread myCallableThread = new Thread(futureTask); myCallableThread.setName("MyFutureTask-test"); myCallableThread.start(); System.out.println("Run by Thread:" + futureTask.get()); } } class MyCallableThread implements Callable<String> { @Override public String call() throws Exception { return Thread.currentThread().getName(); } }
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