Re: [Boost-users] boost mutex locks

Subject: Re: [Boost-users] boost mutex locks
From: Matheus Araújo Aguiar (matheus.pit_at_[hidden])
Date: 2009-07-15 10:29:00

Hello,

On Wed, Jul 15, 2009 at 8:53 AM, mike_wilson <me95mlp_at_[hidden]> wrote:

>
> Hi,
>
> I am a newbie to C++ multi threading (did a bit in java) and would like for
> information on the following...
>
> consider:-
>
> class MyClass
> {
>   void SetMyObject(SomeClass const& value)
>   {
>      boost::mutex::scoped_lock lock(objectMutex);
>      myObject = value;
>   }
>   SomeClass SetMyObject() const
>   {
>      boost::mutex::scoped_lock lock(objectMutex);
>      return myObject;
>   }
> private:
>   SomeClass myObject;
>   boost::mutex objectMutex;
> };
>
>
> Say one thread accesses the SetMyObject() , given that there is a lock in
> the function, it will also lock the  GetMyObject()  blocking any other
> thread from calling?
>
Yes. Since you use the same mutex in both methods, whenever a thread
constructs the lock with the mutex, another thread that later constructs
other lock using the same mutex will be blocked until the mutex is unlocked,
or in other words, until the lock object is destructed (in your code that
happens when the methods 'get' and 'set' ends).

>
> This kind of implies that wherever in the object there is a lock, any
> function owned by the object will be locked to any other thread trying to
> access. Is this correct?

In the code you submited above, yes. But note that the lock object performs
locks and unlocks on a given mutex. So if you use different mutexes in
different methods, you'll get some other behaviour.

>
>
> Thanks again for your help.
> --
> View this message in context:
> http://www.nabble.com/boost-mutex-locks-tp24406812p24406812.html
> Sent from the Boost - Users mailing list archive at Nabble.com.
>
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users
>

PS: in the code you submited, the 'get method' is named SetMyObject. No
trouble for me understanding that and ignoring it, but other people may be
more picky.

Regards,

-- 
Matheus Araújo Aguiar
Computer Scientist
matheus.pit_at_[hidden]