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Threads with SDL within C++ classes

jmakitalo · 2014-09-27T12:40:14

I'm planning on trying out SDL 1.2 threads for my cross-platform game to run some specific tasks. At first a terrain data streamer (even though there may be better ways to do this directly). I'm trying first to figure out how to make a C++ class based design so that the required mutexes would be contained within the class and it would be safe to use the class interface. Below I tried to envision a class for processing some data (here just an array of integers) by a separate thread. The idea is that the main thread creates an instance of the class and then requests work to be done by method requestWorkToBeDone(). The main thread can then ask for the status of the work by getStatus() and acquire the processed data by getData(). The class should be responsible for appropriate mutexes. enum EStatus { statusIdle, statusWorking, statusDone }; class MyClass { public: ~MyClass(); bool init(); // Create thread and mutex, allocate data. static int threadFuncMediator(void *p) // called by SDL_CreateThread to run threadFunc() in separate thread. { return (static_cast<MyClass*>p)->threadFunc(); } void getStatus(EStatus &_status) const { SDL_mutexP(mutex); _status = status; SDL_mutexV(mutex); } bool requestWorkToBeDone(int someParameter) { SDL_mutexP(mutex); if(status!=statusIdle){ SDL_mutexV(mutex); return false; } status = statusWorking; // Use someParameter to specify work ... SDL_mutexV(mutex); return true; } bool getData(int *_data) { SDL_mutexP(mutex); if(status!=statusDone){ SDL_mutexV(mutex); return false; } memcpy(_data, data, sizeof(int)*numData); status = statusIdle; SDL_mutexV(mutex); retrurn true; } private: SDL_Thread *thread; SDL_mutex *mutex; EStatus status; int numData; int *data; // This runs in a thread created by init() via threadFuncMediator(). // Calls getStatus() to see if work should be done. // When work is done, calls setStatus(statusDone); int threadFunc(); }; The thing I'm worried is that threadFunc() also has to call getStatus() to see if it should do work or not. But the instance of the class is owned by the main thread, so is this function call itself safe, eventhough data handling within the function is handled with mutexes?

General and Gameplay Programming Programming

Started by jmakitalo September 24, 2014 01:26 PM

10 comments, last by TheComet 9 years, 6 months ago

jmakitalo

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September 25, 2014 02:26 PM

Valid does not do what you think it does, it does not signal when the future has a result. However, you could probably use one of the timed wait functions with an immediate timeout.

Ah, ok. From cppreference.com about wait_for(): "A steady clock is used to measure the duration. This function may block for longer than timeout_duration due to scheduling or resource contention delays. The "may block for longer" does not sound promising. I'm getting the feeling that this approach is not the proper way for an interactive application.

You really should upgrade to Ubuntu 14.04 as soon as you can. Yes, libSDL2 is available there, and it's already ported natively to the Mir display server so you can develop targeting desktop, tablet, and phone right away. There's really no reason to hold back.

Yes, no reason to hold back. Except my lazyness... have to take backups and maybe improve my current situation by separating Ubuntu and Win7 to their own SSD:s. Can you rely on installing a new Ubuntu version via apt-get nowdays, or does it still tend to break things ?