http://heipark.iteye.com/blog/1393847

newFixedThreadPool內部有個任務隊列，假設線程池里有3個線程，提交了5個任務，那么后兩個任務就放在任務隊列了，即使前3個任務sleep或者堵塞了，也不會執行后兩個任務，除非前三個任務有執行完的

newFixedThreadPool使用范例：

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?

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Java代碼??

import?java.io.IOException;??

import?java.util.concurrent.ExecutorService;??

import?java.util.concurrent.Executors;??

??

public?class?Test?{??

??

????public?static?void?main(String[]?args)?throws?IOException,?InterruptedException?{??

????????ExecutorService?service?=?Executors.newFixedThreadPool(2);??

????????for?(int?i?=?0;?i?<?6;?i++)?{??

????????????final?int?index?=?i;??

????????????System.out.println("task:?"?+?(i+1));??

????????????Runnable?run?=?new?Runnable()?{??

????????????????@Override??

????????????????public?void?run()?{??

????????????????????System.out.println("thread?start"?+?index);??

????????????????????try?{??

????????????????????????Thread.sleep(Long.MAX_VALUE);??

????????????????????}?catch?(InterruptedException?e)?{??

????????????????????????e.printStackTrace();??

????????????????????}??

????????????????????System.out.println("thread?end"?+?index);??

????????????????}??

????????????};??

????????????service.execute(run);??

????????}??

????}??

}??

?

輸出： task: 1
task: 2
thread start0
task: 3
task: 4
task: 5
task: 6
task: 7
thread start1
task: 8
task: 9
task: 10
task: 11
task: 12
task: 13
task: 14
task: 15

?

? ? 從實例可以看到for循環并沒有被固定的線程池阻塞住，也就是說所有的線程task都被提交到了ExecutorService中，查看?Executors.newFixedThreadPool()如下：

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public static ExecutorService newFixedThreadPool(int nThreads) {
return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>());
}

? ? 可以看到task被提交都了LinkedBlockingQueue中。這里有個問題，如果任務列表很大，一定會把內存撐爆，如何解決？看下面：

?

?

Java代碼??

import?java.io.IOException;??

import?java.util.concurrent.ArrayBlockingQueue;??

import?java.util.concurrent.BlockingQueue;??

import?java.util.concurrent.ThreadPoolExecutor;??

import?java.util.concurrent.TimeUnit;??

??

public?class?Test?{??

??

????public?static?void?main(String[]?args)?throws?IOException,?InterruptedException?{??

??????????

????????BlockingQueue<Runnable>?queue?=?new?ArrayBlockingQueue<Runnable>(3);??

??????????

????????ThreadPoolExecutor?executor?=?new?ThreadPoolExecutor(3,?3,?1,?TimeUnit.HOURS,?queue,?new?ThreadPoolExecutor.CallerRunsPolicy());??

??????????

????????for?(int?i?=?0;?i?<?10;?i++)?{??

????????????final?int?index?=?i;??

????????????System.out.println("task:?"?+?(index+1));??

????????????Runnable?run?=?new?Runnable()?{??

????????????????@Override??

????????????????public?void?run()?{??

????????????????????System.out.println("thread?start"?+?(index+1));??

????????????????????try?{??

????????????????????????Thread.sleep(Long.MAX_VALUE);??

????????????????????}?catch?(InterruptedException?e)?{??

????????????????????????e.printStackTrace();??

????????????????????}??

????????????????????System.out.println("thread?end"?+?(index+1));??

????????????????}??

????????????};??

????????????executor.execute(run);??

????????}??

????}??

}??

?

輸出： task: 1
task: 2
thread start1
task: 3
task: 4
task: 5
task: 6
task: 7
thread start2
thread start7
thread start6

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? ? 線程池最大值為4（？？這里我不明白為什么是設置值+1，即3+1，而不是3），準備執行的任務隊列為3。可以看到for循環先處理4個task，然后把3個放到隊列。這樣就實現了自動阻塞隊列的效果。記得要使用ArrayBlockingQueue這個隊列，然后設置容量就OK了。

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