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I have 2 processes which share a queue which is synchronized by a mutex and conditions. I have the following code in one of my processes.

named_mutex mutex(open_only, "MyMutex");

int main()
{
   while(1)
   {
      scoped_lock <named_mutex> lock(mutex)
      //do some processing 
   }
}

My question is whether the mutex has scope throughout all calls in the while loop or does it need to be acquired each time the while loop starts? What is the scope of the mutex for it to be unlocked? It seems each time at the end of the while loop the mutex is unlocked.

Thanks

rudasi
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2 Answers2

10

It behaves exactly the same as any other local variable within a loop body: It will be created and destroyed once per itereation. In this case it will lock and unlock the mutex once per iteration.

Mark B
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0

A scoped_lock, as the name suggests, locks a mutex on creation (in its ctor) and unlocks it on deletion (in its dtor).

Since the scope of the lock instance is within the while body, the mutex is locked when the scoped_lock is created, and unlocked whenever the while loop ends: should a break or continue, or even a return statement be found, or simply when the end of the while body is reached, once for each loop.

Enoah Netzach
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    Your answer is ambiguous; what does *when the while loop ends* mean? At the end of each iteration, or when you break out of the loop? – Praetorian Jul 18 '13 at 17:06
  • I used singular, one loop, no all the loops. The exact time is when the program goes out of the `while` scope, then when a `break`, `continue` instruction is found, or simply when it reaches the end of the body. – Enoah Netzach Jul 18 '13 at 17:16