Daily Archives: April 17, 2008

In this universe we obey the law of commutativity

This kind of thing has happened to be a few times now, so I thought I’d share the fun.

In one of our pieces of software we have a process that looks like this:

void MyThread()
    while (true)

While FunctionA and FunctionB are conceptually similar, they interact with completely different systems.

We had a problem with FunctionA the other day–it was taking 120 seconds to do its thing instead of the normal 10 (or less) because a remote server was down. This caused problems for FunctionB because it wasn’t running as often as it should have so things were getting backed up in the system. Oops.

Now, the solution is to split these two functions into two independent threads so they don’t interfere with each other, and I’ve been meaning to do this for a while, so that’s what I proposed.

Response back: “That’s a good idea, but before we do something complicated like that, can we just put FunctionB first?

Um, no.

The time we want to minimize is the time between running FunctionB, which is TimeSleep + TimeA. Putting FunctionB first makes it TimeA + TimeSleep. Last I checked, those were actually equivalent.

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