Re: using mutexes

James Kanze <>
Tue, 12 Feb 2008 02:31:07 -0800 (PST)
On Feb 12, 6:07 am, iceman <> wrote:

Suppose that my program is such that

int counter;
pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;
void *functionC()
   pthread_mutex_lock( &mutex1 );
   printf("Counter value: %d\n",counter);
   pthread_mutex_unlock( &mutex1 );

int main()
     pthread_t thread_id;
     pthread_create (&thread_id, NULL, &functionC, NULL);
    //increment counter in main also

That looks more like Posix C than anything C++. You really
should ask in a Posix (Unix) group, rather than here.

Will there be a problem when I do this?

Not if you synchronize the access to counter in main as well.
The Posix rule (which, I believe, will be the C++ rule when C++
adds threading in the next version) is simple: if any thread
modifies an object, and more than one thread accesses the
object, then all accesses must be externally synchronized.

If the thread is schduled first
will the main() wait untill the thread unlocks?

Why should it?

If not,Is there anyway to lock the variable in the main
program as well as in the thread.

The same way you locked it in the thread.

James Kanze (GABI Software)
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