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转: Executor类
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Executor框架是指java 5中引入的一系列并發(fā)庫(kù)中與executor相關(guān)的一些功能類，其中包括線程池，Executor，Executors，ExecutorService，CompletionService，Future，Callable等。
他們的關(guān)系為：
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并發(fā)編程的一種編程方式是把任務(wù)拆分為一些列的小任務(wù)，即Runnable，然后在提交給一個(gè)Executor執(zhí)行，Executor.execute(Runnalbe)?。Executor在執(zhí)行時(shí)使用內(nèi)部的線程池完成操作。
一、創(chuàng)建線程池
Executors類，提供了一系列工廠方法用于創(chuàng)先線程池，返回的線程池都實(shí)現(xiàn)了ExecutorService接口。
public static ExecutorService newFixedThreadPool(int nThreads)
創(chuàng)建固定數(shù)目線程的線程池。
public static ExecutorService newCachedThreadPool()
創(chuàng)建一個(gè)可緩存的線程池，調(diào)用execute?將重用以前構(gòu)造的線程（如果線程可用）。如果現(xiàn)有線程沒(méi)有可用的，則創(chuàng)建一個(gè)新線程并添加到池中。終止并從緩存中移除那些已有 60 秒鐘未被使用的線程。
public static ExecutorService newSingleThreadExecutor()
創(chuàng)建一個(gè)單線程化的Executor。
public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize)
創(chuàng)建一個(gè)支持定時(shí)及周期性的任務(wù)執(zhí)行的線程池，多數(shù)情況下可用來(lái)替代Timer類。
Java代碼??
Executor?executor?=?Executors.newFixedThreadPool(10);??Runnable?task?=?new?Runnable()?{??????@Override??????public?void?run()?{??????????System.out.println("task?over");??????}??};??executor.execute(task);????executor?=?Executors.newScheduledThreadPool(10);??ScheduledExecutorService?scheduler?=?(ScheduledExecutorService)?executor;??scheduler.scheduleAtFixedRate(task,?10,?10,?TimeUnit.SECONDS);?? ?二、ExecutorService與生命周期
ExecutorService擴(kuò)展了Executor并添加了一些生命周期管理的方法。一個(gè)Executor的生命周期有三種狀態(tài)，運(yùn)行?，關(guān)閉?，終止。Executor創(chuàng)建時(shí)處于運(yùn)行狀態(tài)。當(dāng)調(diào)用ExecutorService.shutdown()后，處于關(guān)閉狀態(tài)，isShutdown()方法返回true。這時(shí)，不應(yīng)該再想Executor中添加任務(wù)，所有已添加的任務(wù)執(zhí)行完畢后，Executor處于終止?fàn)顟B(tài)，isTerminated()返回true。
如果Executor處于關(guān)閉狀態(tài)，往Executor提交任務(wù)會(huì)拋出unchecked exception RejectedExecutionException。
Java代碼??
ExecutorService?executorService?=?(ExecutorService)?executor;??while?(!executorService.isShutdown())?{??????try?{??????????executorService.execute(task);??????}?catch?(RejectedExecutionException?ignored)?{????????????????}??}??executorService.shutdown();?? ?三、使用Callable，Future返回結(jié)果
Future<V>代表一個(gè)異步執(zhí)行的操作，通過(guò)get()方法可以獲得操作的結(jié)果，如果異步操作還沒(méi)有完成，則，get()會(huì)使當(dāng)前線程阻塞。FutureTask<V>實(shí)現(xiàn)了Future<V>和Runable<V>。Callable代表一個(gè)有返回值得操作。
Java代碼??
Callable<Integer>?func?=?new?Callable<Integer>(){??????public?Integer?call()?throws?Exception?{??????????System.out.println("inside?callable");??????????Thread.sleep(1000);??????????return?new?Integer(8);??????}?????????};????????FutureTask<Integer>?futureTask??=?new?FutureTask<Integer>(func);??Thread?newThread?=?new?Thread(futureTask);??newThread.start();????try?{??????System.out.println("blocking?here");??????Integer?result?=?futureTask.get();??????System.out.println(result);??}?catch?(InterruptedException?ignored)?{??}?catch?(ExecutionException?ignored)?{??}?? ?ExecutoreService提供了submit()方法，傳遞一個(gè)Callable，或Runnable，返回Future。如果Executor后臺(tái)線程池還沒(méi)有完成Callable的計(jì)算，這調(diào)用返回Future對(duì)象的get()方法，會(huì)阻塞直到計(jì)算完成。
例子：并行計(jì)算數(shù)組的和。
Java代碼??
package?executorservice;????import?java.util.ArrayList;??import?java.util.List;??import?java.util.concurrent.Callable;??import?java.util.concurrent.ExecutionException;??import?java.util.concurrent.ExecutorService;??import?java.util.concurrent.Executors;??import?java.util.concurrent.Future;??import?java.util.concurrent.FutureTask;????public?class?ConcurrentCalculator?{????????private?ExecutorService?exec;??????private?int?cpuCoreNumber;??????private?List<Future<Long>>?tasks?=?new?ArrayList<Future<Long>>();????????????class?SumCalculator?implements?Callable<Long>?{??????????private?int[]?numbers;??????????private?int?start;??????????private?int?end;????????????public?SumCalculator(final?int[]?numbers,?int?start,?int?end)?{??????????????this.numbers?=?numbers;??????????????this.start?=?start;??????????????this.end?=?end;??????????}????????????public?Long?call()?throws?Exception?{??????????????Long?sum?=?0l;??????????????for?(int?i?=?start;?i?<?end;?i++)?{??????????????????sum?+=?numbers[i];??????????????}??????????????return?sum;??????????}??????}????????public?ConcurrentCalculator()?{??????????cpuCoreNumber?=?Runtime.getRuntime().availableProcessors();??????????exec?=?Executors.newFixedThreadPool(cpuCoreNumber);??????}????????public?Long?sum(final?int[]?numbers)?{??????????????????for?(int?i?=?0;?i?<?cpuCoreNumber;?i++)?{??????????????int?increment?=?numbers.length?/?cpuCoreNumber?+?1;??????????????int?start?=?increment?*?i;??????????????int?end?=?increment?*?i?+?increment;??????????????if?(end?>?numbers.length)??????????????????end?=?numbers.length;??????????????SumCalculator?subCalc?=?new?SumCalculator(numbers,?start,?end);??????????????FutureTask<Long>?task?=?new?FutureTask<Long>(subCalc);??????????????tasks.add(task);??????????????if?(!exec.isShutdown())?{??????????????????exec.submit(task);??????????????}??????????}??????????return?getResult();??????}????????????public?Long?getResult()?{??????????Long?result?=?0l;??????????for?(Future<Long>?task?:?tasks)?{??????????????try?{??????????????????????????????????Long?subSum?=?task.get();??????????????????result?+=?subSum;??????????????}?catch?(InterruptedException?e)?{??????????????????e.printStackTrace();??????????????}?catch?(ExecutionException?e)?{??????????????????e.printStackTrace();??????????????}??????????}??????????return?result;??????}????????public?void?close()?{??????????exec.shutdown();??????}??}?? ?Main
Java代碼??
int[]?numbers?=?new?int[]?{?1,?2,?3,?4,?5,?6,?7,?8,?10,?11?};??ConcurrentCalculator?calc?=?new?ConcurrentCalculator();??Long?sum?=?calc.sum(numbers);??System.out.println(sum);??calc.close();?? ?四、CompletionService
在剛在的例子中，getResult()方法的實(shí)現(xiàn)過(guò)程中，迭代了FutureTask的數(shù)組，如果任務(wù)還沒(méi)有完成則當(dāng)前線程會(huì)阻塞，如果我們希望任意字任務(wù)完成后就把其結(jié)果加到result中，而不用依次等待每個(gè)任務(wù)完成，可以使CompletionService。生產(chǎn)者submit()執(zhí)行的任務(wù)。使用者take()已完成的任務(wù)，并按照完成這些任務(wù)的順序處理它們的結(jié)果?。也就是調(diào)用CompletionService的take方法是，會(huì)返回按完成順序放回任務(wù)的結(jié)果，CompletionService內(nèi)部維護(hù)了一個(gè)阻塞隊(duì)列BlockingQueue，如果沒(méi)有任務(wù)完成，take()方法也會(huì)阻塞。修改剛才的例子使用CompletionService：
Java代碼??
public?class?ConcurrentCalculator2?{????????private?ExecutorService?exec;??????private?CompletionService<Long>?completionService;??????????private?int?cpuCoreNumber;????????????class?SumCalculator?implements?Callable<Long>?{??????????......??????}????????public?ConcurrentCalculator2()?{??????????cpuCoreNumber?=?Runtime.getRuntime().availableProcessors();??????????exec?=?Executors.newFixedThreadPool(cpuCoreNumber);??????????completionService?=?new?ExecutorCompletionService<Long>(exec);??????????}????????public?Long?sum(final?int[]?numbers)?{??????????????????for?(int?i?=?0;?i?<?cpuCoreNumber;?i++)?{??????????????int?increment?=?numbers.length?/?cpuCoreNumber?+?1;??????????????int?start?=?increment?*?i;??????????????int?end?=?increment?*?i?+?increment;??????????????if?(end?>?numbers.length)??????????????????end?=?numbers.length;??????????????SumCalculator?subCalc?=?new?SumCalculator(numbers,?start,?end);???????????????if?(!exec.isShutdown())?{??????????????????completionService.submit(subCalc);??????????????????}????????????????????????}??????????return?getResult();??????}????????????public?Long?getResult()?{??????????Long?result?=?0l;??????????for?(int?i?=?0;?i?<?cpuCoreNumber;?i++)?{??????????????????????????try?{??????????????????Long?subSum?=?completionService.take().get();??????????????????result?+=?subSum;?????????????????????????}?catch?(InterruptedException?e)?{??????????????????e.printStackTrace();??????????????}?catch?(ExecutionException?e)?{??????????????????e.printStackTrace();??????????????}??????????}??????????return?result;??????}????????public?void?close()?{??????????exec.shutdown();??????}??} ?
轉(zhuǎn)載于:https://www.cnblogs.com/codershuai/p/4413988.html
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