CODEWITHSUNDEEP
c++openmp
henrikz
henrikz

Reputation: 43

OpenMP critical sections in called classes (different than parallel loop)

My question concerns OpenMP critical sections in classes called by a parallellized for-loop which is not part of the same class as the critical section(s). Can critical sections be used this way?

Here is an example:

class TestFunction
{
    TestFunction( SomeSharedObject& _obj) : obj_(_obj) {}
    public:
    void possibly_change_sharedobj( ) 
    {
        #pragma omp critical(myCriticalSection)
        {
            obj_.do_something();
        }
    }
    SomeSharedobject& obj_;
};

class ClassWithParallelloop
{
     void parallelloop()
     {
         #pragma omp parallel for
         for( int i = 0; i < N; ++i)
         {
             TestFunction testfn( myobj_);
             testfn.possibly_change_sharedobj();
         } 
     }
     SomeSharedObject myobj_; 
 };

Q: is the shared object (myobj_) protected against concurrent changes?

Upvotes: 1

Views: 727

Answers (1)

sehe
sehe

Reputation: 393467

No, myobj_ is not "protected against concurrent changes", because that's not what critical sections do.

What they do, is prevent code in those sections from running simultaneously. So, as long as you guarantee that no code outside the critical section(s)* access myobj_, you'll have prevented concurrent access (this is implicit protection).

Answering the other question: It is not a problem (not even relevant) that the omp ciritical pragma is not inside the omp parallel section, lexically.

Upvotes: 1

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