Thread-safe sequential number generator in ColdFusion?

Question

If I have a Generator.cfc with methods:

numeric function next()
{
    return variables.num++;   // Is ++ an atomic operation??
}

And:

application.generator = new generator();

If every request calls application.generator.next(), will this generator ever generate the same number twice on heavy load? In another word... is this thread-safe? If not, where should the lock be?

Answer 1

You can make it atomic by wrapping the increment in a lock. Since ++ requires three operations (fetch, add, store) I don't think it's atomic on its own on any platform.

Answer 2

Yep, as Donnie pointed out CFLOCK is your friend here.

Answer 3

You could also look into the Java 5 class Atomic Integer

The ColdFusion code you need is something like this (I haven't tested it):

<cfset i = createObject("java", "java.util.concurrent.atomic.AtomicInteger").init(startValue) />
<cfset newValue = i.incrementAndGet() />