Re: Efficient way to synchronize bool variables

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.language,microsoft.public.vc.mfc

Date:

Wed, 11 Nov 2009 08:20:38 -0500

Message-ID:

<eFq0HHtYKHA.1336@TK2MSFTNGP06.phx.gbl>

Faisal wrote:

In my program there are boolean vaiables which are shared between a
number of threads.

In the below code m_bRunning and m_bStopped are shared variables. The
function Execute() can be called from any of the threads.I want to
synchronize the accessing of the variable.

void OnStart()
{
m_bStopped = false;
m_bRunning = true;
}

void OnStop()
{
m_bRunning = false;
}

void Execute()
{
if( m_bRunning )
{
// RunningTask()
}
else
{
if( !m_bStopped )
{
// FinalizeTask()
m_bStopped = true;
}
}
}

Does simply declaring the variables as volatile would solve my
problem?
Or do i need interlockedXXX functions here.

I suspect neither will help, but it depends on precisely what "your =
problem" is that you are trying to solve. For example, what should =
happen if m_bRunning turns false while RunningTask is executing? Is it =
OK to run RunningTask in parallel with FinalizeTask? Is it OK for =
FinalizeTask to be run more than once by multiple threads (many threads =
can enter Execute at once and see =
m_bRunning==m_bStopped==false)?

What is the right way to solve this type of problems?

I'd start with _formulating_ it.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not =
necessarily a good idea. It is hard to be sure where they are going to =
land, and it could be dangerous sitting under them as they fly overhead. =
-- RFC 1925