造輪子之MemorySafeLinkedBlockingQueue-LinkBlockingQueue改進

LinkBlockingQueue改進

問題背景

https://github.com/apache/dubbo/pull/9722/files
使用線程池的同學對于標題中的隊列想必都有過使用
 ，但上述隊列使用不當時則會造成程序OOM ，那怎么來控制呢？

使用ArrayBlockingQueue
？如何來評估長度？

是否有一個完美的解決方案呢，MemorySafeLinkedBlockingQueue則通過對內存的限制判斷盡面控制隊列的容量，完成解決了可能存在的OOM問題 
。

獲取內存大?。ㄗ?：單位大B；支持準實時更新）：

Runtime.getRuntime().freeMemory()//JVM中已經申請到的堆內存中還未使用的大小Runtime.getRuntime().maxMemory()// JVM可從操作系統(tǒng)申請到的最大內存值 -XxmRuntime.getRuntime().totalMemory()// JVM已從操作系統(tǒng)申請到的內存大小 —Xxs可設置該值大小-初始堆的大小

線程池在excute任務時，放隊列，放不進去，使用新線程運行任務
。這個放不進行 ，是使用的offer??非阻塞方法嗎 ？

參考 ：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int        int c = ctl.get();     	//工作線程數(shù)<核心線程數(shù)        if (workerCountOf(c) < corePoolSize) {             //進入if，代表可以創(chuàng)建 核心 線程數(shù)            if (addWorker(command, true))                return;            //如果沒進入if，代表創(chuàng)建核心線程數(shù)失敗
，重新獲取 ctl            c = ctl.get();        }        //判斷線程池為Running狀態(tài)

	，將任務添加入阻塞隊列
，使用offer        if (isRunning(c) && workQueue.offer(command)) {             int recheck = ctl.get();            //再次判斷是否為Running狀態(tài)
，若不是Running狀態(tài)，remove任務            if (! isRunning(recheck) && remove(command))                reject(command);            //如果線程池在Running狀態(tài)	，線程池數(shù)量為0            else if (workerCountOf(recheck) == 0)                //阻塞隊列有任務
，但是沒有工作線程
，添加一個任務為空的工作線程處理阻塞隊列中的任務                addWorker(null, false);        }        //阻塞隊列已滿
，創(chuàng)建非核心線程	，拒絕策略-addWorker中有判斷核心線程數(shù)是否超過最大線程數(shù)        else if (!addWorker(command, false))            reject(command);    }

空閑內存計算

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 lock            refresh();            if (refreshStarted.compareAndSet(false, true)) {                 ScheduledExecutorService scheduledExecutorService = Executors.newSingleThreadScheduledExecutor(new NamedThreadFactory("Dubbo-Memory-Calculator"));                // check every 50 ms to improve performance                scheduledExecutorService.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 (percentage <= 0 || percentage >1) {             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);    }}

內存安全隊列

package com.zte.sdn.oscp.queue;import java.util.Collection;import java.util.concurrent.LinkedBlockingQueue;import java.util.concurrent.TimeUnit;public class MemorySafeLinkedBlockingQueueextends LinkedBlockingQueue{     private static final long serialVersionUID = 8032578371739960142L;    public static int THE_256_MB = 256 * 1024 * 1024;    private int maxFreeMemory;    private Rejectorrejector;    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 version        this.rejector = new DiscardPolicy<>();    }    public MemorySafeLinkedBlockingQueue(final Collection<? extends E>c,                                         final int maxFreeMemory) {         super(c);        this.maxFreeMemory = maxFreeMemory;        //default as DiscardPolicy to ensure compatibility with the old version        this.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 Rejectorrejector) {         this.rejector = rejector;    }    /**     * determine if there is any remaining free memory.     *     * @return true if has free memory     */    public boolean hasRemainedMemory() {         return MemoryLimitCalculator.maxAvailable() >maxFreeMemory;    }    @Override    public void put(final E e) throws InterruptedException {         if (hasRemainedMemory()) {             super.put(e);        } else {             rejector.reject(e, this);        }    }    @Override    public 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);    }    @Override    public boolean offer(final E e) {         if (!hasRemainedMemory()) {             rejector.reject(e, this);            return false;        }        return super.offer(e);    }}

拒絕策略

注意其中的rejector是拒絕策略 ，默認的DiscardPolicy什么也不處理；

而DiscardOldPolicy的處理邏輯很簡單

public class DiscardOldestPolicyimplements Rejector{     @Override    public void reject(final E e, final Queuequeue) {         queue.poll();        queue.offer(e);    }}

AbortPolicy則直接拋出異常

public class AbortPolicyimplements Rejector{     @Override    public void reject(final E e, final Queuequeue) {         throw new RejectException("no more memory can be used !");    }}

個人建議增加日志打印即可。

投稿時間：2022-09-09  最后更新：2022-09-09