Jump to content

  • Log In with Google      Sign In   
  • Create Account


Interface and Gameloop - Thread safety


Old topic!
Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.

  • You cannot reply to this topic
3 replies to this topic

#1 gnomgrol   Members   -  Reputation: 583

Like
0Likes
Like

Posted 02 May 2014 - 01:12 PM

Well met!

 

This might be a rather basic question, but I can't seem to find an answer.

To put it simply, I've got two threads - one for the interface and one for the gameloop of my engine. 

Most simple example I could think of: 

 

I've got a button. When I press it, I want to move an object. So what an idiot like me would try is:

void spawnButton_Click(System::Object^  sender, System::EventArgs^  e) {
    Control->ModelEditor->MoveModel("object1", 100, 0, 0);
}

Well, that works like 99% of the time. But sometimes, it crashes - when I try to change the position, while the rendering thread is reading it.

My workaround was to send a request to the gameloop, which it would process on its next runthrough in its own thread. That seems to be working, but it blows up the code by a big deal on the log run, since I have to make request-methods for every single method I want to be accessable from the outside of my engine. 

 

I suppose, some other kind of cross-thread-safety is required here - but I couldn't find something that would be taking considerably less code than my approach. Everything regarding multithreading appears to be a huge pain in the butt to implement, so people try to keep thread-communication to a minimum. 

 

What is the usual approach for this kind of high-traffic-multi-thread-communication? Do you got some good papers to link for help? Everything would be helpful.

 

Have a nice day!

-gnomgrol


Edited by gnomgrol, 02 May 2014 - 01:15 PM.


Sponsor:

#2 DiegoSLTS   Members   -  Reputation: 1092

Like
0Likes
Like

Posted 02 May 2014 - 02:46 PM

Have you tried with semaphores? You don't need a lot of code to implement them.



#3 SeanMiddleditch   Members   -  Reputation: 5078

Like
2Likes
Like

Posted 02 May 2014 - 03:14 PM

My workaround was to send a request to the gameloop, which it would process on its next runthrough in its own thread. That seems to be working, but it blows up the code by a big deal on the log run, since I have to make request-methods for every single method I want to be accessable from the outside of my engine.


This is the best model. If you're finding too much repetition, restructure your code to be more generic. You shouldn't need a whole separate method for each possible edit action. You ideally need only a single "change property" method / command, with possibly a few variations for different types of property edits.

Restructure enough and even in single-threaded code this can simplify a lot. For each edit action initiated by the GUI, create a new instance of some EditAction sub-class (ChangePropertyEditAction, CreateObjectEditAction, etc.). Push this into a queue. Execute the queue later. This pattern also becomes very useful when it comes time to implement undo, as each of your action classes can have both an Apply and an Undo method, letting you play the list of actions forwards or backwards to arrive at the desired state.

Not fully compliant code, but the gist would be:

class IEditAction {
public:
  virtual ~IEditAction() = default;

  virtual void Apply(GameState&) = 0;
  virtual void Undo(GameState&) = 0;
};

class ChangePropertyEditAction : public IEditAction {
  string _propertyName;
  string _targetObjectName;
  string _currentValue;
  string _oldValue;

public:
  virtual void Apply(GameState& gs) override {
    gs.get(_targetObjectName)->setProperty(_propertyName, _newValue);
  }

  virtual void Undo(GameState& gs) override {
    gs.get(_targetObjectName)->setProperty(_propertyName, _currentValue);
  }
};

...

void onMove(string object, vec4 oldPosition, vec4 newPosition) {
  actionQueue.push_back(new ChangePropertyEditAction(object, "position", to_string(oldPosition), to_string(newPosition));
}
The code can use templates to avoid the strings, be more robust, actually compile, etc., but that should give you the idea. For more, look at the "command pattern."

#4 L. Spiro   Crossbones+   -  Reputation: 13213

Like
1Likes
Like

Posted 02 May 2014 - 03:18 PM

Do you got some good papers to link for help?

I am writing this chapter right now in my book. In the meantime:
http://www.gamedev.net/topic/650640-is-using-static-variables-for-input-engine-evil/#entry5113267
http://www.gamedev.net/topic/641102-frame-independent-movement-and-slowdowns/#entry5049391


L. Spiro
It is amazing how often people try to be unique, and yet they are always trying to make others be like them. - L. Spiro 2011
I spent most of my life learning the courage it takes to go out and get what I want. Now that I have it, I am not sure exactly what it is that I want. - L. Spiro 2013
I went to my local Subway once to find some guy yelling at the staff. When someone finally came to take my order and asked, “May I help you?”, I replied, “Yeah, I’ll have one asshole to go.”
L. Spiro Engine: http://lspiroengine.com
L. Spiro Engine Forums: http://lspiroengine.com/forums




Old topic!
Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.



PARTNERS