java并发编程-Executor框架
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Executor框架是指java 5中引入的一系列并发库中与executor相关的一些功能类,其中包括线程池,Executor,Executors,ExecutorService,CompletionService,Future,Callable等。他们的关系为:
并发编程的一种编程方式是把任务拆分为一些列的小任务,即Runnable,然后在提交给一个Executor执行,Executor.execute(Runnalbe)。Executor在执行时使用内部的线程池完成操作。
一、创建线程池
Executors类,提供了一系列工厂方法用于创先线程池,返回的线程池都实现了ExecutorService接口。
public static ExecutorService newFixedThreadPool(intnThreads)
创建固定数目线程的线程池。
public static ExecutorServicenewCachedThreadPool()
创建一个可缓存的线程池,调用execute将重用以前构造的线程(如果线程可用)。如果现有线程没有可用的,则创建一个新线程并添加到池中。终止并从缓存中移除那些已有 60秒钟未被使用的线程。
public static ExecutorServicenewSingleThreadExecutor()
创建一个单线程化的Executor。
public static ScheduledExecutorService
创建一个支持定时及周期性的任务执行的线程池,多数情况下可用来替代Timer类。
- Executor
executor 10);= Executors.newFixedThreadPool( - 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与生命周期
ExecutorService扩展了Executor并添加了一些生命周期管理的方法。一个Executor的生命周期有三种状态,运行,关闭 ,终止。Executor创建时处于运行状态。当调用ExecutorService.shutdown()后,处于关闭状态,isShutdown()方法返回true。这时,不应该再想Executor中添加任务,所有已添加的任务执行完毕后,Executor处于终止状态,isTerminated()返回true。
如果Executor处于关闭状态,往Executor提交任务会抛出unchecked exceptionRejectedExecutionExcepti
- ExecutorService
executorService = (ExecutorService) executor; - while
(!executorService.isShutdown()) { -
try { -
executorService.execute(task); -
} catch (RejectedExecutionExcepti on ignored) { -
-
} - }
- executorService.shutdown();
三、使用Callable,Future返回结果
Future代表一个异步执行的操作,通过get()方法可以获得操作的结果,如果异步操作还没有完成,则,get()会使当前线程阻塞。FutureTask实现了Future和Runable。Callable代表一个 有返回值得操作。
- Callable
func new= Callable(){ -
public Integer throwscall() Exception { -
System.out.println("inside callable" ); -
Thread.sleep(1000); -
return new Integer( 8); -
} - };
- FutureTask
futureTask = new FutureTask(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) { - }
例子:并行计算数组的和。
- 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> newtasks = ArrayList>(); -
-
// 内部类 -
class SumCalculator implementsCallable { -
private int[] numbers; -
private int start; -
private int end; -
-
public SumCalculator( finalint[] numbers, intstart, intend) { -
this.numbers = numbers; -
this.start = start; -
this.end = end; -
} -
-
public Long throwscall() Exception { -
Long sum = 0l; -
for ( inti = start; i < end; i++) { -
sum += numbers[i]; -
} -
return sum; -
} -
} -
-
public ConcurrentCalculator() { -
cpuCoreNumber = Runtime.getRuntime().availableProcessors(); -
exec = Executors.newFixedThreadPool(cpuCoreNumber); -
} -
-
public Long finalsum( int[] numbers) { -
// 根据CPU核心个数拆分任务,创建FutureTask并提交到Executor -
for ( inti 0;= i < cpuCoreNumber; i++) { -
int increment 1;= numbers.length / cpuCoreNumber + -
int start = increment * i; -
int end = increment * i + increment; -
if (end > numbers.length) -
end = numbers.length; -
SumCalculator subCalc = new SumCalculator(numbers, start, end); -
FutureTask task = new FutureTask(subCalc); -
tasks.add(task); -
if (!exec.isShutdown()) { -
exec.submit(task); -
} -
} -
return getResult(); -
} -
-
-
public Long getResult() { -
Long result = 0l; -
for (Future task : tasks) { -
try { -
// 如果计算未完成则阻塞 -
Long subSum = task.get(); -
result += subSum; -
} catch (InterruptedException e) { -
e.printStackTrace(); -
} catch (ExecutionException e) { -
e.printStackTrace(); -
} -
} -
return result; -
} -
-
public void close() { -
exec.shutdown(); -
} - }
- 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
在刚在的例子中,getResult()方法的实现过程中,迭代了FutureTask的数组,如果任务还没有完成则当前线程会阻塞,如果我们希望任意字任务完成后就把其结果加到result中,而不用依次等待每个任务完成,可以使CompletionService。生产者submit()执行的任务。使用者take()已完成的任务,并按照完成这些任务的顺序处理它们的结果。也就是调用CompletionService的take方法是,会返回按完成顺序放回任务的结果,CompletionService内部维护了一个阻塞队列BlockingQueue,如果没有任务完成,take()方法也会阻塞。修改刚才的例子使用CompletionService:
- public
class ConcurrentCalculator2 { -
-
private ExecutorService exec; -
private CompletionService completionService; -
-
-
private int cpuCoreNumber; -
-
// 内部类 -
class SumCalculator implementsCallable { -
...... -
} -
-
public ConcurrentCalculator2() { -
cpuCoreNumber = Runtime.getRuntime().availableProcessors(); -
exec = Executors.newFixedThreadPool(cpuCoreNumber); -
completionService = new ExecutorCompletionServic e(exec); -
-
-
} -
-
public Long finalsum( int[] numbers) { -
// 根据CPU核心个数拆分任务,创建FutureTask并提交到Executor -
for ( inti 0;= i < cpuCoreNumber; i++) { -
int increment 1;= numbers.length / cpuCoreNumber + -
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 ( inti 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(); -
} - }
- 转载自:http://www.iteye.com/topic/366591
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