Re: [Boost-users] Need a help about boost.thread

From: Steven Woody (narkewoody_at_[hidden])
Date: 2007-10-06 12:12:59

On 10/4/07, Steven Woody <narkewoody_at_[hidden]> wrote:
> On 10/4/07, KSpam <keesling_spam_at_[hidden]> wrote:
> > Woody,
> >
> > All you have to do is protect the shared data with a boost::mutex.  You will
> > want to protect any methods that access or mutate the data.  Boost has a
> > nice "scoped_lock".  The scoped_lock will set a lock and automatically unset
> > the lock when it goes out of scope.  If multiple threads reach this code, the
> > first thread will set the lock and the other threads will wait until the lock
> > is unset.  This effectively makes the section of code protected by a
> > scoped_lock single threaded.  Here is a quick-and-dirty example:
> >
> > class ThreadSafeData
> > {
> > public:
> >     typedef std::vector<float> FloatVector;
> >
> >     // Accessor (return by value)
> >     FloatVector getFloats (void) const
> >     {
> >         boost::mutex::scoped_lock lock(m_Mutex);
> >         return m_Floats;
> >     }
> >
> >     // Mutator
> >     void addFloat (float value)
> >     {
> >         boost::mutex::scoped_lock lock(m_Mutex);
> >         m_Floats.push_back(value);
> >     }
> >
> >     // Mutator
> >     void clearFloats (void)
> >     {
> >          boost::mutex::scoped_lock lock(m_Mutex);
> >         m_Floats.clear();
> >     }
> >
> > private:
> >     boost::mutex m_Mutex;
> >     FloatVector m_Floats;
> > }
> >
> > Notice I am returning data by value instead of const reference!  You do not
> > want multiple threads keeping references around to shared data.  Also, notice
> > that this code does not concern itself with how the threads are created.  It
> > simply takes care of protecting the data from multiple threads (however they
> > are created).
> >
> > I hope that this helps!
> >
> > Justin
> >
>

sorry for i repost below message for i really need your kind help.

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thanks a lot for your code which cleared most of my question.  while
the scoped_lock can has a thread block when a mutex object is being
locked by another thread, can you show me additional example about how
to let a thread immediately exit when it found a mutex object is being
used?  i mean that one of thread in our application is actually the
GUI main thread, it will access the shared data in it's OnIdel event
handler, so i hope it will be never blocked, when resources are not
available, i hope it can immediately exist and try again some times
later.  does the boost support this kind of feature? thanks.
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