1.慎用FixedThreadPool
看一下FixedThreadPool的构造方法
/**
* Creates a thread pool that reuses a fixed number of threads
* operating off a shared unbounded queue. At any point, at most
* {@code nThreads} threads will be active processing tasks.
* If additional tasks are submitted when all threads are active,
* they will wait in the queue until a thread is available.
* If any thread terminates due to a failure during execution
* prior to shutdown, a new one will take its place if needed to
* execute subsequent tasks. The threads in the pool will exist
* until it is explicitly {@link ExecutorService#shutdown shutdown}.
*
* @param nThreads the number of threads in the pool
* @return the newly created thread pool
* @throws IllegalArgumentException if {@code nThreads <= 0}
*/
public static ExecutorService newFixedThreadPool(int nThreads) {
return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>());
}
注意最后一行的LinkedBlockingQueue,这是一个无界队列,如果消费能力跟不上,那么就会在这个无界队列中无限制的增加task,内存就会被打爆,妥妥的让你写casestudy外加diss code reviewer。
顺便看下Alibaba命名规范中对线程池使用的要求
【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: 1) 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 。 2) 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 。
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