线程池 - ThreadPoolExecutor
ThreadPoolExecutor 构造方法
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
ThreadFactory threadFactory,
RejectedExecutionHandler handler)
ThreadPoolExecutor构造参数 - 1
ThreadPoolExecutor构造参数 - 2
ThreadPoolExecutor核心方法 - 1
ThreadPoolExecutor核心方法 - 2
线程池类结构图
ThreadPoolExecutor是其中功能最为强大的线程池类，重点掌握。
线程池接口
newCachedThreadPool(),newFixedThreadPool(),
newScheduledThreadPool(),newSingleThreadExecutor()内部追踪后，其实都是设定参数后返回ThreadPoolExecutor实例。
public static ExecutorService newCachedThreadPool() {
return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
60L, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>());
}
public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
60L, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
threadFactory);
}
public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>(),
threadFactory);
}
public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
return new ScheduledThreadPoolExecutor(corePoolSize);
}
// ====>
public ScheduledThreadPoolExecutor(int corePoolSize) {
super(corePoolSize, Integer.MAX_VALUE, 0, NANOSECONDS,
new DelayedWorkQueue());
}
// ====>
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue) {
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
Executors.defaultThreadFactory(), defaultHandler);
}
public static ExecutorService newSingleThreadExecutor() {
return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>()));
}
public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {
return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>(),
threadFactory));
}
注意，上述Executors返回实例是
ThreadPoolExecutor，但是接口引用为ExecutorService，这将导致一个问题，那就是可供调用的API实际是变少了，所以阿里Java开发手册中有一项是禁用Executors来初始化线程池。
【强制】线程池不允许使用
Executors去创建,而是通过ThreadPoolExecutor的方式,这样
的处理方式让写的同学更加明确线程池的运行规则,规避资源耗尽的风险。
说明:Executors返回的线程池对象的弊端如下:
FixedThreadPool和SingleThreadPool:
允许的请求队列长度为 Integer.MAX_VALUE ,可能会堆积大量的请求,从而导致 OOM 。CachedThreadPool和ScheduledThreadPool:
允许的创建线程数量为 Integer.MAX_VALUE ,可能会创建大量的线程,从而导致 OOM 。
package com.accat.concurrency.example.threadPool;
import lombok.extern.slf4j.Slf4j;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
@Slf4j
public class ThreadPoolExample1 {
public static void main(String[] args) {
ExecutorService executorService = Executors.newCachedThreadPool();
for (int i = 0; i < 10; i++) {
final int index = i;
executorService.execute(new Runnable() {
@Override
public void run() {
log.info("task:{}", index);
}
});
}
executorService.shutdown();
}
}
package com.accat.concurrency.example.threadPool;
import lombok.extern.slf4j.Slf4j;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
@Slf4j
public class ThreadPoolExample2 {
public static void main(String[] args) {
ExecutorService executorService = Executors.newFixedThreadPool(3);
for (int i = 0; i < 10; i++) {
final int index = i;
executorService.execute(new Runnable() {
@Override
public void run() {
log.info("task:{}", index);
}
});
}
executorService.shutdown();
}
}
package com.accat.concurrency.example.threadPool;
import lombok.extern.slf4j.Slf4j;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
@Slf4j
public class ThreadPoolExample3 {
public static void main(String[] args) {
ExecutorService executorService = Executors.newSingleThreadExecutor();
for (int i = 0; i < 10; i++) {
final int index = i;
executorService.execute(new Runnable() {
@Override
public void run() {
log.info("task:{}", index);
}
});
}
executorService.shutdown();
}
}
package com.accat.concurrency.example.threadPool;
import lombok.extern.slf4j.Slf4j;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
@Slf4j
public class ThreadPoolExample4 {
public static void main(String[] args) {
ScheduledExecutorService executorService = Executors.newScheduledThreadPool(1);
executorService.scheduleAtFixedRate(new Runnable() {
@Override
public void run() {
log.warn("schedule run");
}
}, 1, 3, TimeUnit.SECONDS);
Timer timer = new Timer();
timer.schedule(new TimerTask() {
@Override
public void run() {
log.warn("timer run");
}
}, new Date(), 5 * 1000);
}
}
线程池大小的合理配置建议
