ThreadPoolExecutor的參數理解
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。
1. newFixedThreadPool()
創建線程數固定大小的線程池。
2.newSingleThreadPool()
創建線程數為1的線程池，
3.newCachedThreadPool()
創建可緩沖的線程池。沒有大小限制
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<Runnable> 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，當線程數大于corePoolSize的空閑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、當線程數小于corePoolSize時，創建線程執行任務。
2、當線程數大于等于corePoolSize并且workQueue沒有滿時，放入workQueue中
3、線程數大于等于corePoolSize并且當workQueue滿時，新任務新建線程運行，線程總數要小于maximumPoolSize
4、當線程總數等于maximumPoolSize并且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方法并且阻塞執行
3、ThreadPoolExecutor.DiscardPolicy() 直接丟棄后來的任務
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<Runnable> workQueue = new LinkedBlockingQueue<Runnable>();
BlockingQueue<Runnable> workQueue = new ArrayBlockingQueue<Runnable>(5);
ThreadFactory threadFactory = Executors.defaultThreadFactory();
//線程池和隊列滿了之后的處理方式
//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);
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