From 10fffca8b2808e2b00094795328d96dec2789e99 Mon Sep 17 00:00:00 2001
From: LamGC <lam827@lamgc.net>
Date: Fri, 1 Jan 2021 09:29:51 +0800
Subject: [PATCH] =?UTF-8?q?[Fix]=20CacheStore-Local=20=E4=BF=AE=E5=A4=8D?=
 =?UTF-8?q?=20AutoCleanTimer=20=E5=9B=A0=E9=80=BB=E8=BE=91=E9=94=99?=
 =?UTF-8?q?=E8=AF=AF=E6=9C=AA=E8=83=BD=E5=8F=8A=E6=97=B6=E8=BD=AE=E8=AF=A2?=
 =?UTF-8?q?=E6=B8=85=E7=90=86=20Cleanable=20=E7=9A=84=E9=97=AE=E9=A2=98;?=
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[Fix] AutoCleanTimer 调整 'run()' 方法, 修复轮询执行错误并改善无效 Cleanable Reference 的清除方式;

Bug Description: 当发现 Reference 的指向为 null 时, 在收集了该对象后将会直接 return 导致后续轮询结束.
---
 .../cgj/bot/cache/local/AutoCleanTimer.java   | 56 ++++++++++++++-----
 1 file changed, 42 insertions(+), 14 deletions(-)

diff --git a/ContentGrabbingJi-CacheStore-local/src/main/java/net/lamgc/cgj/bot/cache/local/AutoCleanTimer.java b/ContentGrabbingJi-CacheStore-local/src/main/java/net/lamgc/cgj/bot/cache/local/AutoCleanTimer.java
index 4019c4a..3bfca2d 100644
--- a/ContentGrabbingJi-CacheStore-local/src/main/java/net/lamgc/cgj/bot/cache/local/AutoCleanTimer.java
+++ b/ContentGrabbingJi-CacheStore-local/src/main/java/net/lamgc/cgj/bot/cache/local/AutoCleanTimer.java
@@ -5,14 +5,12 @@ import com.google.common.util.concurrent.ThreadFactoryBuilder;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.lang.ref.ReferenceQueue;
 import java.lang.ref.WeakReference;
 import java.util.HashSet;
-import java.util.Iterator;
 import java.util.Set;
-import java.util.concurrent.CopyOnWriteArraySet;
-import java.util.concurrent.ScheduledExecutorService;
-import java.util.concurrent.ScheduledThreadPoolExecutor;
-import java.util.concurrent.TimeUnit;
+import java.util.concurrent.*;
+import java.util.concurrent.atomic.AtomicReference;
 
 /**
  * 定时清理机制.
@@ -34,37 +32,63 @@ public class AutoCleanTimer implements Runnable {
 
     private final static Logger log = LoggerFactory.getLogger(AutoCleanTimer.class);
 
+    private final static AtomicReference<ReferenceQueue<Cleanable>> REFERENCE_QUEUE = new AtomicReference<>(null);
+
     static {
         SCHEDULED_EXECUTOR.scheduleAtFixedRate(new AutoCleanTimer(), 100L, 100L, TimeUnit.MILLISECONDS);
         Runtime.getRuntime().addShutdownHook(new Thread(SCHEDULED_EXECUTOR::shutdownNow, "ShutdownThread-AutoClean"));
     }
 
     /**
-     * 增加需要定时执行清理的缓存库
+     * 增加需要定时执行清理的缓存库.
      * @param store 已实现Cleanable的对象
      */
     public static void add(Cleanable store) {
-        CLEANABLE_STORE_SET.add(new WeakReference<>(store));
+        CLEANABLE_STORE_SET.add(new WeakReference<>(store, REFERENCE_QUEUE.get()));
+    }
+
+    /**
+     * 移除对指定 Cleanable 的轮询.
+     * @param store 欲停止轮询的 Cleanable 对象.
+     */
+    public static void remove(final Cleanable store) {
+        CLEANABLE_STORE_SET.removeIf(cleanableReference -> cleanableReference.get() == store);
+    }
+
+    /**
+     * 获取当前被轮询的 Cleanable 数量.
+     * @return 返回轮询的 Cleanable 数量.
+     */
+    public static int size() {
+        return CLEANABLE_STORE_SET.size();
+    }
+
+    /**
+     * 设置虚引用回收队列, 以检查虚引用对象回收状况.
+     * <p> 本方法用于诊断 AutoCleanTimer 对虚引用对象的处理情况, 一般情况下无需使用.
+     * @param queue 引用队列.
+     */
+    public static void setWeakReferenceQueue(ReferenceQueue<Cleanable> queue) {
+        REFERENCE_QUEUE.set(queue);
     }
 
     private AutoCleanTimer() {}
 
+    private final Set<WeakReference<Cleanable>> toBeCleanReference = new HashSet<>();
+
     @Override
     public void run() {
         if (CLEANABLE_STORE_SET.size() == 0) {
             return;
         }
 
-        Iterator<WeakReference<Cleanable>> iterator = CLEANABLE_STORE_SET.iterator();
-        Set<WeakReference<Cleanable>> toBeCleanReference = new HashSet<>();
-        while(iterator.hasNext()) {
-            WeakReference<Cleanable> reference = iterator.next();
+        for (WeakReference<Cleanable> reference : CLEANABLE_STORE_SET) {
             Cleanable store = reference.get();
-            if (store == null) {
+            if (reference.isEnqueued() || store == null) {
                 // 由于 COW ArraySet 的 Iterator 不支持 remove 操作,
                 // 所以先收集起来, 等完成所有清理工作后统一删除引用.
                 toBeCleanReference.add(reference);
-                return;
+                continue;
             }
             try {
                 store.clean();
@@ -72,6 +96,10 @@ public class AutoCleanTimer implements Runnable {
                 log.error("{} 执行清理动作时发生异常:\n{}", store.toString(), Throwables.getStackTraceAsString(e));
             }
         }
-        CLEANABLE_STORE_SET.removeAll(toBeCleanReference);
+
+        if (toBeCleanReference.size() != 0) {
+            CLEANABLE_STORE_SET.removeAll(toBeCleanReference);
+            toBeCleanReference.clear();
+        }
     }
 }