ConcurrentModificationException on creating Config

[toboro]

Hi,

first of all, this is a great api. We use it for about half a year and it is very handy :-) great work!

Now we get an Exception in a multithreaded environment. I analysed it, and found out, that it occurs when the system properties are modified, while a owner Config object is created:

Caused by: java.util.ConcurrentModificationException
	at java.util.Hashtable$Enumerator.next(Hashtable.java:1167)
	at java.util.Hashtable.putAll(Hashtable.java:586)
	at org.aeonbits.owner.VariablesExpander.<init>(VariablesExpander.java:31)
	at org.aeonbits.owner.DefaultFactory.create(DefaultFactory.java:42)
	at org.aeonbits.owner.ConfigFactory.create(ConfigFactory.java:66)

I wrote a junit testcase to reproduce it. And I also found a Workaround for it, by use another SystemProvider (from your api) which take a copy from the system properties made with an enumeration, because enumerations don't throw ConcurrentModificationExceptions.

Here is the testcase:

package org.aeonbits.owner;

import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicBoolean;
import org.aeonbits.owner.Util.SystemProvider;
import org.junit.Test;

public class OwnerTest {

  public static interface SomeConfig extends Config {
    //
  }

  @Test
  public void testSystemProperties() throws Exception {

    //uncomment the next line to get the test working...
//    setAlternateSystemProvider();

    ExecutorService exe = Executors.newFixedThreadPool(2);
    try {
      final AtomicBoolean running = new AtomicBoolean(true);

      Future<Void> configLoader = exe.submit(new Callable<Void>() {
        @Override
        public Void call() throws Exception {
          //on most tries it fails on the first iteration.
          for(int cnt = 0; cnt < 100; cnt++) {
            ConfigFactory.create(SomeConfig.class);
          }
          return null;
        }
      });

      Future<Void> sysPropModifier = exe.submit(new Callable<Void>() {
        @Override
        public Void call() throws Exception {
          while (running.get()) {
            System.setProperty("Foo", "Bar");
            System.getProperties().remove("Foo");
          }
          return null;
        }
      });

      configLoader.get();
      running.set(false);
      sysPropModifier.get();
    }
    finally {
      exe.shutdown();
    }
  }

  private static void setAlternateSystemProvider() {
    Util.system = new SystemProvider() {
      @Override
      public String getProperty(String key) {
        return System.getProperty(key);
      }

      @Override
      public Map<String, String> getenv() {
        return System.getenv();
      }

      @Override
      public Properties getProperties() {
        Properties res = new Properties();
        Enumeration<Object> keys = System.getProperties().keys();
        while(keys.hasMoreElements()) {
          Object key = keys.nextElement();
          Object value = System.getProperties().get(key);
          if(value != null) {
            res.put(key, value);
          }
        }
        return res;
      }
    };
  }
}

[lviggiano]

Wow. Great finding. I'll check it out. Thanks. L.

[richmidwinter]

Might be better off replacing the contents of that getProperties() method with a clone() call:

public Properties getProperties() { return (Properties) System.getProperties().clone(); }

[lviggiano]

👍

[hoterran]

@lviggiano this is confused bug for a long time。 can release new version after fix it ?

[lviggiano]

resolved by pull request #241
will be released asap