线程池最佳线程数量到底要如何配置?
Hollis
共 5706字,需浏览 12分钟
·
2020-11-20 21:13
一、前言
二、从实战开始
public class MyCallable implements Callable<String> {
public String call() throws Exception {
System.out.println("MyCallable call");
return "success";
}
public static void main(String[] args) {
ExecutorService threadPool = Executors.newSingleThreadExecutor();
try {
Future
future = threadPool.submit(new MyCallable()); System.out.println(future.get());
} catch (Exception e) {
System.out.println(e);
} finally {
threadPool.shutdown();
}
}
}
三、创建线程池的方法
public class MyWorker implements Runnable {
public void run() {
System.out.println("MyWorker run");
}
public static void main(String[] args) {
ExecutorService threadPool = Executors.newFixedThreadPool(8);
try {
threadPool.execute(new MyWorker());
} catch (Exception e) {
System.out.println(e);
} finally {
threadPool.shutdown();
}
}
}
public class MyTask implements Runnable {
public void run() {
System.out.println("MyTask call");
}
public static void main(String[] args) {
ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(8);
try {
scheduledExecutorService.schedule(new MyRunnable(), 60, TimeUnit.SECONDS);
} finally {
scheduledExecutorService.shutdown();
}
}
}
四、自定义线程池
corePoolSize:核心线程数
maximumPoolSize:最大线程数
keepAliveTime:空闲线程回收时间间隔
unit:空闲线程回收时间间隔单位
workQueue:提交任务的队列,当线程数量超过核心线程数时,可以将任务提交到任务队列中。比较常用的有:ArrayBlockingQueue; LinkedBlockingQueue; SynchronousQueue;
threadFactory:线程工厂,可以自定义线程的一些属性,比如:名称或者守护线程等
handler:表示当拒绝处理任务时的策略
ThreadPoolExecutor.AbortPolicy:丢弃任务并抛出RejectedExecutionException异常。
ThreadPoolExecutor.DiscardPolicy:也是丢弃任务,但是不抛出异常。
ThreadPoolExecutor.DiscardOldestPolicy:丢弃队列最前面的任务,然后重新尝试执行任务(重复此过程)
ThreadPoolExecutor.CallerRunsPolicy:由调用线程处理该任务
public class MyThreadPool implements Runnable {
private static final ExecutorService executorService = new ThreadPoolExecutor(
8,
10,
30,
TimeUnit.SECONDS,
new ArrayBlockingQueue<>(500),
new ThreadPoolExecutor.AbortPolicy());
public void run() {
System.out.println("MyThreadPool run");
}
public static void main(String[] args) {
int availableProcessors = Runtime.getRuntime().availableProcessors();
try {
executorService.execute(new MyThreadPool());
} catch (Exception e) {
System.out.println(e);
} finally {
executorService.shutdown();
}
}
}
五、最佳线程数
什么是IO密集型? 比如:频繁读取磁盘上的数据,或者需要通过网络远程调用接口。 什么是CPU密集型? 比如:非常复杂的调用,循环次数很多,或者递归调用层次很深等。
int availableProcessors = Runtime.getRuntime().availableProcessors();
最佳线程数目 = ((线程等待时间+线程CPU时间)/线程CPU时间 )* CPU数目
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