Thread Safety

Why RuleBook and Rule are transient, and how to get a fresh one every time.

Thread Safety

Call getInstance() for each use. RuleBook and Rule are transient (non-singleton) objects, so every getInstance() call gives you a new one that nobody else is touching.

var greeting = getInstance( "HelloWorld" )
	.run( { name : "World" } )
	.getResult()
	.getValue()

Why

given() and run( facts ) write facts onto the instance itself, and the result and the rule status audit trail live there too. One RuleBook instance is not safe to run() from several threads at once, or with different facts in separate calls. A RuleBook instance is only safe to run() again if it is given the exact same facts it already holds.

Do not keep a RuleBook in a singleton property or a shared scope, and do not inject one with a plain inject="HelloWorld" into a singleton. That gives the singleton one instance for its whole life.

Safe ways to get a RuleBook

• getInstance( "MyRuleBook" ) in the place you use it, for a RuleBook class.
• ruleBook( "name" ) in handlers, views and layouts, for a rulebook declared in config. It returns a fresh RuleBook every call.
• inject="rulebook:name" for the same declared rulebooks, in any class. It injects a small provider, not a RuleBook. Call .get() where you use it to get a fresh RuleBook, so it is safe even in a singleton:

class singleton{

	property name="creditRules" inject="rulebook:credit";

	function decide( score ){
		return creditRules.get().run( { creditScore : score } ).getResult().getValue()
	}

}

The Builder

Builder@rulebox itself is a @singleton @threadsafe class. It is safe to share one instance of the builder across threads, since it only hands back fresh RuleBook and Rule transients and holds no request-specific state itself.