[GitHub] [commons-pool] aooohan commented on pull request #182: Avoid potential ConcurrentModificationException by using Iterator.

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aooohan commented on PR #182:
URL: https://github.com/apache/commons-pool/pull/182#issuecomment-1283987610

   Hi @garydgregory 
   
   Sorry for the late reply.
   
   The following is unit test.
   ```java
           try (final GenericObjectPool<String, RuntimeException> pool = new GenericObjectPool<>(new BasePooledObjectFactory<String, RuntimeException>() {
               @Override
               public String create() {
                   return null;
               }
               @Override
               public PooledObject<String> wrap(final String obj) {
                   return new DefaultPooledObject<>(obj);
               }
           })) {
               for (int i = 0; i < 1000; i++) {
                   final BaseGenericObjectPool<String, RuntimeException>.Evictor evictor2 = pool.new Evictor();
                   EvictionTimer.schedule(evictor2, Duration.ofSeconds(10), Duration.ofSeconds(30));
               }
               System.gc();
               System.out.println("gc结束");
               TimeUnit.SECONDS.sleep(100);
           }
   ```
   There are two steps：
   
   1. If you run it straight away, nothing appears to be happening.
   2.  if you modify `Reaper` a bit, you'll see that it actually throws a `ConcurrentModificationException`, but I haven't figured out why the exception isn't thrown in the first step.
   ```java
   private static class Reaper implements Runnable {
           @Override
           public void run() {
               synchronized (EvictionTimer.class) {
                   try {
                       for (final Entry<WeakReference<BaseGenericObjectPool<?, ?>.Evictor>, WeakRunner<BaseGenericObjectPool<?, ?>.Evictor>> entry : TASK_MAP
                               .entrySet()) {
                           if (entry.getKey().get() == null) {
                               executor.remove(entry.getValue());
                               TASK_MAP.remove(entry.getKey());
                           }
                       }
                   } catch (Exception e) {
                       e.printStackTrace();
                       System.out.println(e);
                   }
                   if (TASK_MAP.isEmpty() && executor != null) {
                       executor.shutdown();
                       executor.setCorePoolSize(0);
                       executor = null;
                   }
               }
           }
       }
   ```
   
   
   
   


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