Multithreaded Programming and Hyper-Threading Technology

Listing 1: OpenMP enables parallelization of loops or regions without large-scale code modifications.

//-- Avoid overhead by entering a parallel section once, then dividing the
//   work within the parallel section.
#pragma omp parallel
{
    //-- Only the master thread executes the following function call
    #pragma omp master
    MasterThreadFunc();
    //-- The threads that process this loop continue immediately to the next
    //   block without waiting for all threads to finish this loop
    #pragma omp for nowait
    for( i = 0; i < X; i++ )
    {
        doWork();
        // ...
    }
    //-- Any thread may excute this; generally it is likely to be the first
    //   thread to complete its work from the above loop
    #pragma omp single
    OneTimeAnyThreadFunc();
    //-- The threads that process this loop will synchronize at the end of
    //   the loop before continuing execution
    #pragma omp for
    for( i = 0; i < Y; i++ )
    {
        doOtherWork();
        // ...
    }
    //-- Sections instruct OpenMP to divide the identified sections across
    //   the multiple threads.
    #pragma omp sections
    {
        // These sections are divided among the threads, causing each to be
        // executed exactly once, and in parallel with the other. If the
        // program contains more sections than threads, the remaining
        // sections will be scheduled as threads finish their previously
        // assigned sections.
        #pragma omp section
        {
            doTaskA();
        }
        #pragma omp section
        {
            doTaskB();
        }
        #pragma omp section
        {
            doTaskC();
        }
    }
}