LinkBlockingQueue改进
问题背景
https://github.com/apache/dubbo/pull/9722/files使用线程池的同学对于标题中的队列想必都有过使用，但上述队列使用不当时则会造成程序OOM，那怎么来控制呢？
使用ArrayBlockingQueue？如何来评估长度？
是否有一个完美的解决方案呢，MemorySafeLinkedBlockingQueue则通过对内存的限制判断尽面控制队列的容量，完成解决了可能存在的OOM问题。
获取内存大小（注：单位大B；支持准实时更新）：
Runtime.getRuntime().freeMemory()//JVM中已经申请到的堆内存中还未使用的大小Runtime.getRuntime().maxMemory()// JVM可从操作系统申请到的最大内存值 -XxmRuntime.getRuntime().totalMemory()// JVM已从操作系统申请到的内存大小 —Xxs可设置该值大小-初始堆的大小
线程池在excute任务时，放队列，放不进去，使用新线程运行任务。这个放不进行，是使用的offer??非阻塞方法吗？
参考：https://blog.csdn.net/weixin_43108539/article/details/125190023
public void execute(Runnable command) {if (command == null)throw new NullPointerException(); //拿到32位的intint c = ctl.get(); //工作线程数<核心线程数if (workerCountOf(c) < corePoolSize) {//进入if，代表可以创建 核心 线程数if (addWorker(command, true))return;//如果没进入if，代表创建核心线程数失败，重新获取 ctlc = ctl.get();}//判断线程池为Running状态，将任务添加入阻塞队列，使用offerif (isRunning(c) && workQueue.offer(command)) {int recheck = ctl.get();//再次判断是否为Running状态，若不是Running状态，remove任务if (! isRunning(recheck) && remove(command))reject(command);//如果线程池在Running状态，线程池数量为0else if (workerCountOf(recheck) == 0)//阻塞队列有任务，但是没有工作线程，添加一个任务为空的工作线程处理阻塞队列中的任务addWorker(null, false);}//阻塞队列已满，创建非核心线程，拒绝策略-addWorker中有判断核心线程数是否超过最大线程数else if (!addWorker(command, false))reject(command);}
空闲内存计算
package com.zte.sdn.oscp.queue;import cn.hutool.core.thread.NamedThreadFactory;import java.util.concurrent.Executors;import java.util.concurrent.ScheduledExecutorService;import java.util.concurrent.TimeUnit;import java.util.concurrent.atomic.AtomicBoolean;public class MemoryLimitCalculator {private static volatile long maxAvailable;private static final AtomicBoolean refreshStarted = new AtomicBoolean(false);private static void refresh() {maxAvailable = Runtime.getRuntime().freeMemory();}private static void checkAndScheduleRefresh() {if (!refreshStarted.get()) {// immediately refresh when first call to prevent maxAvailable from being 0// to ensure that being refreshed before refreshStarted being set as true// notice: refresh may be called for more than once because there is no lockrefresh();if (refreshStarted.compareAndSet(false, true)) {ScheduledExecutorService scheduledExecutorService = Executors.newSingleThreadScheduledExecutor(new NamedThreadFactory(“Dubbo-Memory-Calculator”));// check every 50 ms to improve performancescheduledExecutorService.scheduleWithFixedDelay(MemoryLimitCalculator::refresh, 50, 50, TimeUnit.MILLISECONDS);Runtime.getRuntime().addShutdownHook(new Thread(() -> {refreshStarted.set(false);scheduledExecutorService.shutdown();}));}}}/** * Get the maximum available memory of the current JVM. * * @return maximum available memory */public static long maxAvailable() {checkAndScheduleRefresh();return maxAvailable;}/** * Take the current JVM’s maximum available memory * as a percentage of the result as the limit. * * @param percentage percentage * @return available memory */public static long calculate(final float percentage) {if (percentage1) {throw new IllegalArgumentException();}checkAndScheduleRefresh();return (long) (maxAvailable() * percentage);}/** * By default, it takes 80% of the maximum available memory of the current JVM. * * @return available memory */public static long defaultLimit() {checkAndScheduleRefresh();return (long) (maxAvailable() * 0.8);}}
内存安全队列
package com.zte.sdn.oscp.queue;import java.util.Collection;import java.util.concurrent.LinkedBlockingQueue;import java.util.concurrent.TimeUnit;public class MemorySafeLinkedBlockingQueue extends LinkedBlockingQueue {private static final long serialVersionUID = 8032578371739960142L;public static int THE_256_MB = 256 * 1024 * 1024;private int maxFreeMemory;private Rejector rejector;public MemorySafeLinkedBlockingQueue() {this(THE_256_MB);}public MemorySafeLinkedBlockingQueue(final int maxFreeMemory) {super(Integer.MAX_VALUE);this.maxFreeMemory = maxFreeMemory;//default as DiscardPolicy to ensure compatibility with the old versionthis.rejector = new DiscardPolicy();}public MemorySafeLinkedBlockingQueue(final Collection c, final int maxFreeMemory) {super(c);this.maxFreeMemory = maxFreeMemory;//default as DiscardPolicy to ensure compatibility with the old versionthis.rejector = new DiscardPolicy();}/** * set the max free memory. * * @param maxFreeMemory the max free memory */public void setMaxFreeMemory(final int maxFreeMemory) {this.maxFreeMemory = maxFreeMemory;}/** * get the max free memory. * * @return the max free memory limit */public int getMaxFreeMemory() {return maxFreeMemory;}/** * set the rejector. * * @param rejector the rejector */public void setRejector(final Rejector rejector) {this.rejector = rejector;}/** * determine if there is any remaining free memory. * * @return true if has free memory */public boolean hasRemainedMemory() {return MemoryLimitCalculator.maxAvailable() > maxFreeMemory;}@Overridepublic void put(final E e) throws InterruptedException {if (hasRemainedMemory()) {super.put(e);} else {rejector.reject(e, this);}}@Overridepublic boolean offer(final E e, final long timeout, final TimeUnit unit) throws InterruptedException {if (!hasRemainedMemory()) {rejector.reject(e, this);return false;}return super.offer(e, timeout, unit);}@Overridepublic boolean offer(final E e) {if (!hasRemainedMemory()) {rejector.reject(e, this);return false;}return super.offer(e);}}
拒绝策略
注意其中的rejector是拒绝策略，默认的DiscardPolicy什么也不处理；
而DiscardOldPolicy的处理逻辑很简单
public class DiscardOldestPolicy implements Rejector {@Overridepublic void reject(final E e, final Queue queue) {queue.poll();queue.offer(e);}}
AbortPolicy则直接抛出异常
public class AbortPolicy implements Rejector {@Overridepublic void reject(final E e, final Queue queue) {throw new RejectException(“no more memory can be used !”);}}
个人建议增加日志打印即可。
