newCachedThreadPool创建一个可缓存线程池,如果线程池长度超过处理需要,可灵活回收空闲线程,若无可回收,则新建线程。 newFixedThreadPool 创建一个定长线程池,可控制线程最大并发数,超出的线程会在队列中等待。 newScheduledThreadPool 创建一个定长线程池,支持定时及周期性任务执行。 newSingleThreadExecutor创建一个单线程化的线程池,它只会用唯一的工作线程来执行任务,保证所有任务按照指定顺序(FIFO, LIFO, 优先级)执行。
每个线程例子:
ExecutorService e = Executors.newCachedThreadPool();
for (int i = 0; i < 5; i++) {
e.submit(() -> {
String name = Thread.currentThread().getName();
System.out.println("使用CachedThread创建线程:" + name);
});
}
ExecutorService executorService = Executors.newFixedThreadPool(3);
for (int j = 0; j < 5; j++) {
executorService.submit(() -> {
String name = Thread.currentThread().getName();
System.out.println("使用FixedThread创建线程:" + name);
});
}
ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(3);
for (int k = 0; k < 5; k++) {
scheduledExecutorService.schedule(() -> {
String name = Thread.currentThread().getName();
System.out.println("使用ScheduledThread创建线程:" + name);
System.out.println(System.currentTimeMillis());
}, 2, TimeUnit.SECONDS);
}
ExecutorService singleTHread = Executors.newSingleThreadExecutor();
for (int n = 0; n < 5; n++) {
singleTHread.submit(() -> {
String name = Thread.currentThread().getName();
System.out.println("使用SingleThread创建线程:" + name);
});
}
输出:
使用CachedThread创建线程:pool-1-thread-1
使用CachedThread创建线程:pool-1-thread-1
使用CachedThread创建线程:pool-1-thread-1
使用CachedThread创建线程:pool-1-thread-1
使用CachedThread创建线程:pool-1-thread-1
使用FixedThread创建线程:pool-2-thread-1
使用FixedThread创建线程:pool-2-thread-2
使用FixedThread创建线程:pool-2-thread-3
使用FixedThread创建线程:pool-2-thread-1
使用FixedThread创建线程:pool-2-thread-2
使用SingleThread创建线程:pool-4-thread-1
使用SingleThread创建线程:pool-4-thread-1
使用SingleThread创建线程:pool-4-thread-1
使用SingleThread创建线程:pool-4-thread-1
使用SingleThread创建线程:pool-4-thread-1
使用ScheduledThread创建线程:pool-3-thread-1
使用ScheduledThread创建线程:pool-3-thread-3
1550728498308
使用ScheduledThread创建线程:pool-3-thread-2
1550728498308
使用ScheduledThread创建线程:pool-3-thread-3
1550728498308
1550728498308
使用ScheduledThread创建线程:pool-3-thread-2
1550728498309
ThreadFactory namedThreadFactory = new ThreadFactoryBuilder().setNameFormat("demo-pool-%d").build();
ExecutorService pool = new ThreadPoolExecutor(2, 8,
1L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>(20), namedThreadFactory, new ThreadPoolExecutor.AbortPolicy());
for (int n = 0; n < 20; n++) {
pool.submit(() -> {
String name = Thread.currentThread().getName();
System.out.println("使用ThreadPoolExecutor创建线程:" + name);
System.out.println(pool.toString());
});
}
阿里编程规范提示: 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各个方法的弊端: 1)newFixedThreadPool和newSingleThreadExecutor: 主要问题是堆积的请求处理队列可能会耗费非常大的内存,甚至OOM。 2)newCachedThreadPool和newScheduledThreadPool: 主要问题是线程数最大数是Integer.MAX_VALUE,可能会创建数量非常多的线程,甚至OOM。
Positive example 1:
//org.apache.commons.lang3.concurrent.BasicThreadFactory
ScheduledExecutorService executorService = new ScheduledThreadPoolExecutor(1,
new BasicThreadFactory.Builder().namingPattern("example-schedule-pool-%d").daemon(true).build());
Positive example 2:
ThreadFactory namedThreadFactory = new ThreadFactoryBuilder()
.setNameFormat("demo-pool-%d").build();
//Common Thread Pool
ExecutorService pool = new ThreadPoolExecutor(5, 200,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>(1024), namedThreadFactory, new ThreadPoolExecutor.AbortPolicy());
pool.execute(()-> System.out.println(Thread.currentThread().getName()));
pool.shutdown();//gracefully shutdown
Positive example 3:
<bean id="userThreadPool"
class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor">
<property name="corePoolSize" value="10" />
<property name="maxPoolSize" value="100" />
<property name="queueCapacity" value="2000" />
<property name="threadFactory" value= threadFactory />
<property name="rejectedExecutionHandler">
<ref local="rejectedExecutionHandler" />
</property>
</bean>
//in code
userThreadPool.execute(thread);