public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue) {
1、corePoolSize —new ThreadPoolExecutor的時候創建的的線程,
如果ThreadPoolExecutor.execute的任務數>corePoolSize 則會把任務放到BlockingQueue 、如果BlockingQueue滿了會繼續創建新線程、一直到線程個數大於第二個參數maximumPoolSize
2、maximumPoolSize 允許創建的最大線程數、如果BlockingQueue已經滿了、線程數==maximumPoolSize 則會執行ThreadPoolExecutor的拒絕策略
3、keepAliveTime 如果BlockingQueue從滿了到未滿、則大於corePoolSize, 小於maximumPoolSize的線程, 會在keepAliveTime的時間內存活、否則會被回收
參考
https://my.oschina.net/u/2250599/blog/498787
一、使用Executors創建線程池
之前創建線程的時候都是用的Executors的newFixedThreadPool(),newSingleThreadExecutor(),newCachedThreadPool()這三個方法。當然Executors也是用不同的參數去new ThreadPoolExecutor
1. newFixedThreadPool()
創建線程數固定大小的線程池。 由於使用了LinkedBlockingQueue所以maximumPoolSize 沒用，當corePoolSize滿了之後就加入到LinkedBlockingQueue隊列中。每當某個線程執行完成之後就從LinkedBlockingQueue隊列中取一個。所以這個是創建固定大小的線程池。
public static ExecutorService newFixedThreadPool(int nThreads) {
return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue());
}
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue workQueue) {
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
Executors.defaultThreadFactory(), defaultHandler);
}
2.newSingleThreadPool()
創建線程數爲1的線程池，由於使用了LinkedBlockingQueue所以maximumPoolSize 沒用，corePoolSize爲1表示線程數大小爲1,滿了就放入隊列中，執行完了就從隊列取一個。
public static ExecutorService newSingleThreadExecutor() {
return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue()));
}
3.newCachedThreadPool()
創建可緩衝的線程池。沒有大小限制。由於corePoolSize爲0所以任務會放入SynchronousQueue隊列中，SynchronousQueue只能存放大小爲1，所以會立刻新起線程，由於maxumumPoolSize爲Integer.MAX_VALUE所以可以認爲大小爲2147483647。受內存大小限制。
public static ExecutorService newCachedThreadPool() {
return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
60L, TimeUnit.SECONDS,
new SynchronousQueue());
}
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue workQueue) {
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
Executors.defaultThreadFactory(), defaultHandler);
}
二、使用ThreadPoolExecutor創建線程池
ThreadPoolExecutor的構造函數
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue workQueue,
ThreadFactory threadFactory,
RejectedExecutionHandler handler) {
if (corePoolSize < 0 ||
maximumPoolSize <= 0 ||
maximumPoolSize < corePoolSize ||
keepAliveTime < 0)
throw new IllegalArgumentException();
if (workQueue == null || threadFactory == null || handler == null)
throw new NullPointerException();
this.corePoolSize = corePoolSize;
this.maximumPoolSize = maximumPoolSize;
this.workQueue = workQueue;
this.keepAliveTime = unit.toNanos(keepAliveTime);
this.threadFactory = threadFactory;
this.handler = handler;
}
參數：
1、corePoolSize核心線程數大小，當線程數<corePoolSize ，會創建線程執行runnable
2、maximumPoolSize 最大線程數， 當線程數 >= corePoolSize的時候，會把runnable放入workQueue中
3、keepAliveTime 保持存活時間，當線程數大於corePoolSize的空閒線程能保持的最大時間。
4、unit 時間單位
5、workQueue 保存任務的阻塞隊列
6、threadFactory 創建線程的工廠
7、handler 拒絕策略
任務執行順序：
1、當線程數小於corePoolSize時，創建線程執行任務。
2、當線程數大於等於corePoolSize並且workQueue沒有滿時，放入workQueue中
3、線程數大於等於corePoolSize並且當workQueue滿時，新任務新建線程運行，線程總數要小於maximumPoolSize
4、當線程總數等於maximumPoolSize並且workQueue滿了的時候執行handler的rejectedExecution。也就是拒絕策略。
ThreadPoolExecutor默認有四個拒絕策略：
1、ThreadPoolExecutor.AbortPolicy() 直接拋出異常RejectedExecutionException
2、ThreadPoolExecutor.CallerRunsPolicy() 直接調用run方法並且阻塞執行
3、ThreadPoolExecutor.DiscardPolicy() 直接丟棄後來的任務
4、ThreadPoolExecutor.DiscardOldestPolicy() 丟棄在隊列中隊首的任務
當然可以自己繼承RejectedExecutionHandler來寫拒絕策略.
int corePoolSize = 1;
int maximumPoolSize = 2;
int keepAliveTime = 10;
// BlockingQueue workQueue = new LinkedBlockingQueue();
BlockingQueue workQueue = new ArrayBlockingQueue(5);
ThreadFactory threadFactory = Executors.defaultThreadFactory();
//線程池和隊列滿了之後的處理方式
//1.跑出異常
RejectedExecutionHandler handler = new ThreadPoolExecutor.AbortPolicy();
RejectedExecutionHandler handler2 = new ThreadPoolExecutor.CallerRunsPolicy();
RejectedExecutionHandler handler3 = new ThreadPoolExecutor.DiscardPolicy();
RejectedExecutionHandler handler4 = new ThreadPoolExecutor.DiscardOldestPolicy();
ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, TimeUnit.SECONDS, workQueue, threadFactory, handler2);
for (int j = 1; j < 15; j++) {
threadPoolExecutor.execute(new Runnable() {
public void run() {
try {
System.out.println(Thread.currentThread().getName());
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
}
System.out.println(threadPoolExecutor);
}