[gameprogrammer] Re: variables and multithreading

On Wed, 2006-01-18 at 11:46 -0500, Roger D Vargas wrote:
> Can I consider the application main loop like a thread and use mutex 
> operations while running that loop?

The main loop is *a* thread. You have to use a mutex to control access
from *all* threads. Only one thread at a time can be allowed to access
the data. You can use a mutex per record, or a mutex for the entire set
of records. It all depends on what kind of control you need.

                Bob Pendleton

> 
> Stephane Marchesin escribió:
> > Roger D Vargas wrote:
> > 
> >> Im writing a multithreaded server and I have reached the point where I 
> >> have to access the array containing the players data from the main 
> >> loop. Should I use some variable to mark if a record is being modified 
> >> by network thread?
> >>
> > Well, you should use more than a variable, you should use a mutex or a 
> > semaphore (these are special variable s that ensures mutual exclusion 
> > between different threads). If you don't, things will go bad sooner or 
> > later. Even if the network thread is the only one writing to the player 
> > data, it might be preempted in the middle of an update, and the main 
> > thread will read inconsistent data.
> > 
> > I suggest you read a tutorial on mutexes and semaphores (the theory 
> > behind all mutexes/semaphores implementation is the same, only the 
> > function names change). Or you could look at SDL  which implements this 
> > stuff, the functions are quite simple and highly portable :
> > http://www.libsdl.org/cgi/docwiki.cgi/SDL_20API
> > 
> > Stephane
> > 
> > 
> > 
> > 
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> > 
> > 
> 
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