timeout for a mutex lock

dmail · 10-23-2005, 07:22 PM

Is it possible to timeout a mutex lock in posix?

i have mutexs etc in classes, but would this psudeo type code work in c++ as part of the mutex class?

Code:

pthread_mutex_t m;

bool get_lock(time_out)
{
        get the systemtime
        wait = systemtime + time_out;
        volitile bool got_mutex = false;

        while (systemtime < wait && got_mutex == false) 
        {
                if ( mutex->trylock(&m) == EBUSY)
                {
                        get the systemtime;
                }
                else 
                {
                        got_mutex = true;
                }
        }
        return got_mutex;
        
}

any thoughts on this?

cheers

jtshaw · 10-23-2005, 07:37 PM

Sounds very dangerous to me. If you return true and let somebody go off and mess with some sort of shared memory you could end up with some pretty hard to track bugs. It would be better if you just designed your program so it never had a deadlock and the whole timeout would be a moot point.

dmail · 10-23-2005, 07:46 PM

creating the app without deadlocks is what im trying to do, by removing the block on the mutex this ensures there will never be a deadlock. win32 and osx have this feature in there mutex and im just trying to apply it to posix aswell so that my abstract base class(for osx, win and nix) works for all.

if this is not a good way of doing it, is there some flag etc that i can change the blocking time with?

jtshaw · 10-23-2005, 08:01 PM

Well, all I'm saying is this kind of thing allows your program to disguise a potential major problem. Id rather know that my logic was causing a thread to never release a mutex lock then to think it works and find out later one of the threads wasn't really working properly.

dmail · 10-24-2005, 06:30 AM

im a little confused jt, i see what you are saying but can you see a way it would return true yet not having gained the lock?

jtshaw · 10-24-2005, 07:04 AM

Eh.. apparently I'm an idiot

I somehow thought you had the default value of the return as true... As for you logic... I do believe that would work.

dmail · 10-24-2005, 07:22 AM

Quote:

Originally posted by jtshaw
Eh.. apparently I'm an idiot I somehow thought you had the default value of the return as true... As for you logic... I do believe that would work.

lol thanks i thought i was missing something, i wouldnt say idiot, coz that would be someone who thought they were wrong but wouldn't admit it

i know its not the most efficient way(well maybe it is coz i dont know another) but i just wanted to give all os's the same funcs. thanks