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SendMessage Overhead

Discussion in 'Scripting' started by jeffcraighead, Aug 31, 2007.

  1. jeffcraighead

    jeffcraighead

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    What is the overhead of using SendMessage vs. calling a function from a script component directly?

    Jeff
     
    jeffcraighead, Aug 31, 2007
    #1

  2. Daniel_Brauer

    Daniel_Brauer

    Unity Technologies

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    A lot, but it won't matter for most people's code. If performance is a problem and you are using SendMessage in Update, FixedUpdate or in tight loops, see what you can do about caching references and calling methods directly.
     
    Daniel_Brauer, Aug 31, 2007
    #2

  3. bronxbomber92

    bronxbomber92

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    I'd probably think the overhead would be that of several(3+ ?) function calls?

    This is merely a guess though.
     
    bronxbomber92, Aug 31, 2007
    #3

  4. Daniel_Brauer

    Daniel_Brauer

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    I just did a quick test, and in the simplest case (one object, two scripts), SendMessage() is about 100 times slower than a direct call. It becomes even slower as more scripts and functions are added to the object, because SendMessage has to search through all of them for the correct function.
     
    Daniel_Brauer, Aug 31, 2007
    #4

  5. Foxxis

    Foxxis

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    Really? Wow.
    Honestly though, this thread makes me very happy. I know it's wrong, but here's why:
    When I transferred the architecture of my game to Unity from it's humble origins, I stuck with the message system I had devised. In the back of my head I've had plans to rewrite it using SendMessage as I (wrongly) assumed that to be more efficient.

    So, now I won't have to. Another perk of sticking with my own system is that I can pass along more parameters as separate variables as well.

    Anyway, still a bit surprising that it's not more efficient. However, since it has to search perhaps it's inevitable.
     
    Foxxis, Aug 31, 2007
    #5

  6. Jonathan Czeck

    Jonathan Czeck

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    It'd be nice if you posted your test project somewhere. I'm really curious how you tested it reasonably accurately.

    Cheers,
    -Jon
     
    Jonathan Czeck, Aug 31, 2007
    #6

  7. Daniel_Brauer

    Daniel_Brauer

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    Here are the two scripts. I made a new scene, attached both to the camera, and linked the reference for CallTest.otherScript. When Send Message was checked, I got times of about 1.55 seconds, as opposed to times of 0.015 when unchecked.
     

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    Daniel_Brauer, Aug 31, 2007
    #7

  8. Joachim_Ante

    Joachim_Ante

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    I think the comparison is not too good in explaining real world speed. What you are basically seeing is how good to JIT optimizer is vs a real world difference.

    Your function does pretty much nothing, so yes a direct function call that is probably being inlined thus not even being called is a lot faster than SendMessage.
    Message passing needs to find the right method in a hashtable, needs to go through each monobehaviour on the game object etc.

    Generally, if you know who should receive a function then you should definately and absolutely call the function directly. That will always be a lot faster, and everyone loves speed.

    The thing is though, there are a lot of cases where you just don't, where it makes for cleaner design to use message passing. And abstracts implementations in a nice way. The tradeoff for messages is not only speed it is convenience and nice code as well.
     
    Joachim_Ante, Sep 2, 2007
    #8