Re: Avoiding the anonymous variable declaration RAII error...

From:

mark.zaytsev@gmail.com

Newsgroups:

comp.lang.c++.moderated

Date:

Mon, 24 Mar 2008 15:49:17 CST

Message-ID:

<a8a4a057-97c9-467c-8574-6ae5399fa332@p25g2000hsf.googlegroups.com>

On Mar 11, 2:42 pm, "Eric J. Holtman" <e...@ericholtman.com> wrote:

I've burned myself twice in seven or so years doing this, and
it seems like there ought to be a clever way to avoid it:

I have a Mutex class, and a Locker class which acquires
a mutex in its constructor, and releases it in its destructor,
so you can write the standard code:

void
process_threaded_data ()
{
Locker lk (m_mutex);
}

However, it's a massive race condition just waiting to happen
if you forget the "lk", and just write:

void
process_threaded_data ()
{
Locker (m_mutex);
}

Is there some way to design class Locker so that writing the
second piece of code comes up as an error?

This technique was posted here while ago:

inline Locker::operator bool() { return true; }

#define critical_section(m) if ( Locker lk = Locker( m ) )

Usage
void f()
{
     critical_section( m_mutex )
     {
         ...
     }
}

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