team_example.cpp

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Using a Team of AD Threads: Example and Test

Purpose

This example demonstrates how use a team of threads with CppAD.

thread_team

The following three implementations of the team_thread.hpp specifications are included:

team_openmp.cpp

OpenMP Implementation of a Team of AD Threads

team_bthread.cpp

Boost Thread Implementation of a Team of AD Threads

team_pthread.cpp

Pthread Implementation of a Team of AD Threads

Source Code

# include <cppad/cppad.hpp>
# include "team_thread.hpp"
# define NUMBER_THREADS  4

namespace {
   using CppAD::thread_alloc;

   // structure with information for one thread
   typedef struct {
      // function argument (worker input)
      double          x;
      // false if an error occurs, true otherwise (worker output)
      bool            ok;
   } work_one_t;
   // vector with information for all threads
   // (use pointers instead of values to avoid false sharing)
   work_one_t* work_all_[NUMBER_THREADS];
   // --------------------------------------------------------------------
   // function that does the work for one thread
   void worker(void)
   {  using CppAD::NearEqual;
      using CppAD::AD;
      bool ok = true;
      size_t thread_num = thread_alloc::thread_num();

      // CppAD::vector uses the CppAD fast multi-threading allocator
      CppAD::vector< AD<double> > ax(1), ay(1);
      ax[0] = work_all_[thread_num]->x;
      Independent(ax);
      ay[0] = sqrt( ax[0] * ax[0] );
      CppAD::ADFun<double> f(ax, ay);

      // Check function value corresponds to the identity
      double eps = 10. * CppAD::numeric_limits<double>::epsilon();
      ok        &= NearEqual(ay[0], ax[0], eps, eps);

      // Check derivative value corresponds to the identity.
      CppAD::vector<double> d_x(1), d_y(1);
      d_x[0] = 1.;
      d_y    = f.Forward(1, d_x);
      ok    &= NearEqual(d_x[0], 1., eps, eps);

      // pass back ok information for this thread
      work_all_[thread_num]->ok = ok;
   }
}

// This test routine is only called by the master thread (thread_num = 0).
bool team_example(void)
{  bool ok = true;

   size_t num_threads = NUMBER_THREADS;

   // Check that no memory is in use or avialable at start
   // (using thread_alloc in sequential mode)
   size_t thread_num;
   for(thread_num = 0; thread_num < num_threads; thread_num++)
   {  ok &= thread_alloc::inuse(thread_num) == 0;
      ok &= thread_alloc::available(thread_num) == 0;
   }

   // initialize work_all_
   for(thread_num = 0; thread_num < num_threads; thread_num++)
   {  // allocate separate memory for this thread to avoid false sharing
      size_t min_bytes(sizeof(work_one_t)), cap_bytes;
      void*  v_ptr = thread_alloc::get_memory(min_bytes, cap_bytes);
      work_all_[thread_num]     = static_cast<work_one_t*>(v_ptr);
      // in case this thread's worker does not get called
      work_all_[thread_num]->ok = false;
      // parameter that defines the work for this thread
      work_all_[thread_num]->x  = double(thread_num) + 1.;
   }

   ok &= team_create(num_threads);
   ok &= team_work(worker);
   ok &= team_destroy();

   // go down so that free memrory for other threads before memory for master
   thread_num = num_threads;
   while(thread_num--)
   {  // check that this thread was ok with the work it did
      ok &= work_all_[thread_num]->ok;
      // delete problem specific information
      void* v_ptr = static_cast<void*>( work_all_[thread_num] );
      thread_alloc::return_memory( v_ptr );
      // check that there is no longer any memory inuse by this thread
      // (for general applications, the master might still be using memory)
      ok &= thread_alloc::inuse(thread_num) == 0;
      // return all memory being held for future use by this thread
      thread_alloc::free_available(thread_num);
   }
   return ok;
}