A thread safety problem occur when multiple threads share the Rules #418

When accessing through annotations (i.e., generating proxy classes), there is a thread safety problem occur when multiple threads share the Rules

Rule 'rule' performed with error java.util.ConcurrentModificationException
at java.util.TreeMap$PrivateEntryIterator.nextEntry(TreeMap.java:1211)
at java.util.TreeMap$KeyIterator.next(TreeMap.java:1265)
at org.jeasy.rules.core.RuleProxy.executeMethod(RuleProxy.java:140)
at org.jeasy.rules.core.RuleProxy.invoke(RuleProxy.java:109)
at com.sun.proxy.$Proxy142.execute(Unknown Source)
at org.jeasy.rules.support.composite.ActivationRuleGroup.execute(ActivationRuleGroup.java:98)
at org.jeasy.rules.core.DefaultRulesEngine.doFire(DefaultRulesEngine.java:112)
at org.jeasy.rules.core.DefaultRulesEngine.fire(DefaultRulesEngine.java:70)

This is the problematic source code:

package org.jeasy.rules.core;
public class RuleProxy implements InvocationHandler {
//xxxxx
private Set getActionMethodBeans() {
if (this.actionMethods == null) {
this.actionMethods = new TreeSet<>();
Method[] methods = getMethods();
for (Method method : methods) {
if (method.isAnnotationPresent(Action.class)) {
Action actionAnnotation = method.getAnnotation(Action.class);
int order = actionAnnotation.order();
this.actionMethods.add(new ActionMethodOrderBean(method, order));
}
}
}
return this.actionMethods;
}
}

I think a simpler solution would be to add double-checked lock when execute "this.actionMethods = new TreeSet<>();" , to check if "this.actionMethods" is still null.

I have been waiting here for your response. Thank you!!!