About Replacing Annotations with Intel® TBB Code

This topic explains the steps needed to implement parallelism proposed by the Intel Advisor annotations by adding Intel® Threading Building Blocks (Intel® TBB) parallel framework code.

• Add Intel TBB code to add appropriate synchronization of shared resources, using the LOCK annotations as a guide. The following topics cover the Intel TBB synchronization options:

  • About Intel TBB Mutexes
  • Intel TBB Mutex - Example

• Add code to create Intel TBB tasks, using the SITE/TASK annotations as a guide. The following topics cover the Intel TBB task creation options:

  • Parallelize Functions - Intel TBB Tasks
  • Parallelize Data - Intel TBB Counted Loops
  • Parallelize Data - Intel TBB Loops with Complex Iteration Control

This is the recommended order of tasks for replacing the annotations with Intel TBB code:

1. Add appropriate synchronization of shared resources, using LOCK annotations as a guide.
2. Test to verify you did not break anything, before adding the possibility of non-deterministic behavior with parallel tasks.
3. Add code to create Intel TBB tasks or loops, using the SITE/TASK annotations as a guide.
4. Test with one thread, to verify that your program still works correctly.
5. Test with more than one thread to see that the multithreading works as expected.

The Intel TBB parallel framework creates worker threads automatically. In general, you should concern yourself only with the tasks, and leave it to the framework to create and destroy the worker threads.

If you do need some control over creation and destruction of worker threads, read about task_scheduler_init in the Intel TBB Reference manual.

The table below shows the serial, annotated program code in the left column and the equivalent Intel TBB parallel code in the right column for some typical code to which parallelism can be applied.

// Locking
ANNOTATE_LOCK_ACQUIRE();
  Body();
ANNOTATE_LOCK_RELEASE():

// Locking can use various mutex types provided 
// by Intel TBB. For example:
#include <tbb/tbb.h>
 ...
 tbb::mutex g_Mutex;
 ...
{
    tbb::mutex::scoped_lock lock(g_Mutex);
    Body();
}

// Do-All Counted loops, one task
ANNOTATE_SITE_BEGIN(site);
  For (I = 0; I < N; ++) {
    ANNOTATE_ITERATION_TASK(task);
      {statement;}
  }
ANNOTATE_SITE_END();

// Do-All Counted loops, using lambda 
// expressions
#include <tbb/tbb.h>
  ...
  tbb::parallel_for(0,N,[&](int I) { 
    statement;
  });

// Create Multiple Tasks
ANNOTATE_SITE_BEGIN(site);
  ANNOTATE_TASK_BEGIN(task1);
    statement-or-task1;
  ANNOTATE_TASK_END();
  ANNOTATE_TASK_BEGIN(task2);
    statement-or-task2;
  ANNOTATE_TASK_END();
ANNOTATE_SITE_END();

// Create Multiple tasks, using lambda 
// expressions
#include <tbb/tbb.h>

  ...
  tbb::parallel_invoke(
    [&]{statement-or-task1;},
    [&]{statement-or-task2;}
  );

For information about common parallel programming patterns and how to implement them in Intel TBB, see the Intel TBB help topic Design Patterns.