Re: [boost] [interprocess] native Windows cond_var + mutex

Subject: Re: [boost] [interprocess] native Windows cond_var + mutex
From: Ion Gaztañaga (igaztanaga_at_[hidden])
Date: 2011-10-30 17:54:55

El 30/10/2011 21:23, Dan Brown escribió:
> So this would be an issue for objects that have initial state that is
> specified only at creation time not acquisition time, e.g. initial
> semaphore count.  Can't mutexes be created transparently and
> atomically?  I think the same would be true of condition variables.
> So when the last process exits and destroys the mutex or cond_var,
> the next process to acquire it creates it.  There can be logical
> persistence for some objects via their name even if there isn't
> physical persistence.

No, I can create shared memory write anything into it and unmap it. In 
windows it would be destroyed. In UNIX another process could read 
anything the first process has written.

I could take a semaphore to count arrived packets increasing the 
semaphore count for each packet, and then exit producer process. After 
that another process could know how many packets arrived. In windows the 
semaphore would be destroyed and the consumer wouldn't get any information.

The same with a message queue (windows has no native message queue but 
you could do one with shmem and named mutex/condition var). The producer 
can fill the message queue and exit. The consumer takes messages. In 
windows the message queue would be destroyed and data lost.