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Up-> CppAD multi_thread thread_test.cpp simple_ad_pthread.cpp

simple_ad_pthread.cpp

Headings-> Purpose Source Code

# include <cppad/cppad.hpp>
# include <pthread.h>
# define NUMBER_THREADS  4

namespace {
    // structure with problem specific information
    typedef struct {
        // function argument (worker input)
        double          x;
        // This structure would also have return information in it,
        // but this example only returns the ok flag
    } problem_specific;
    // =====================================================================
    // General purpose code you can copy to your application
    // =====================================================================
    using CppAD::thread_alloc;
    // ------------------------------------------------------------------
    // key for accessing thread specific information
    pthread_key_t thread_specific_key_;

    // no need to destroy thread specific information
    void thread_specific_destructor(void* thread_num_vptr)
    {   return; }

    // Are we in sequential mode; i.e., other threads are waiting for
    // master thread to set up next job ?
    bool sequential_execution_ = true;

    // used to inform CppAD when we are in parallel execution mode
    bool in_parallel(void)
    {   return ! sequential_execution_; }

    // used to inform CppAD of current thread number thread_number()
    size_t thread_number(void)
    {   // get thread specific information
        void*   thread_num_vptr = pthread_getspecific(thread_specific_key_);
        size_t* thread_num_ptr  = static_cast<size_t*>(thread_num_vptr);
        size_t  thread_num      = *thread_num_ptr;
        return thread_num;
    }
    // ---------------------------------------------------------------------
    // structure with information for one thread
    typedef struct {
        // number for this thread (thread specific points here)
        size_t            thread_num;
        // pthread unique identifier for this thread
        pthread_t         pthread_id;
        // false if an error occurs, true otherwise
        bool              ok;
        // pointer to problem specific information
        problem_specific* info;
    } thread_one_t;
    // vector with information for all threads
    thread_one_t thread_all_[NUMBER_THREADS];
    // --------------------------------------------------------------------
    // function that initializes the thread and then calls the actual worker
    bool worker(size_t thread_num, problem_specific* info);
    void* run_one_worker(void* thread_num_vptr)
    {   bool ok = true;

        // thread_num for this thread
        size_t thread_num = *static_cast<size_t*>(thread_num_vptr);

        // The master thread should call worker directly
        ok &= thread_num != 0;

        // This is not the master thread, so thread specific infromation
        // has not yet been set. We use it to inform other routines
        // of this threads number.
        // We must do this before calling thread_alloc::thread_num().
        int rc = pthread_setspecific(
            thread_specific_key_,
            thread_num_vptr
        );
        ok &= rc == 0;

        // check the value of thread_alloc::thread_num().
        ok = thread_num == thread_alloc::thread_num();

        // Now do the work
        ok &= worker(thread_num, thread_all_[thread_num].info);

        // pass back ok information for this thread
        thread_all_[thread_num].ok = ok;

        // no return value
        return nullptr;
    }
    // --------------------------------------------------------------------
    // function that calls all the workers
    bool run_all_workers(size_t num_threads, problem_specific* info_all[])
    {   bool ok = true;

        // initialize thread_all_ (execpt for pthread_id)
        size_t thread_num;
        for(thread_num = 0; thread_num < num_threads; thread_num++)
        {   // pointed to by thread specific info for this thread
            thread_all_[thread_num].thread_num = thread_num;
            // initialize as false to make sure worker gets called by other
            // threads. Note that thread_all_[0].ok does not get used
            thread_all_[thread_num].ok         = false;
            // problem specific information
            thread_all_[thread_num].info       = info_all[thread_num];
        }

        // master pthread_id
        thread_all_[0].pthread_id = pthread_self();

        // error flag for calls to pthread library
        int rc;

        // create a key for thread specific information
        rc = pthread_key_create(
            &thread_specific_key_, thread_specific_destructor
        );
        ok &= (rc == 0);

        // set thread specific information for this (master thread)
        void* thread_num_vptr = static_cast<void*>(
            &(thread_all_[0].thread_num)
        );
        rc = pthread_setspecific(thread_specific_key_, thread_num_vptr);
        ok &= (rc == 0);

        // Now thread_number() has necessary information for this thread
        // (number zero), and while still in sequential mode,
        // call setup for using CppAD::AD<double> in parallel mode.
        thread_alloc::parallel_setup(
            num_threads, in_parallel, thread_number
        );
        thread_alloc::hold_memory(true);
        CppAD::parallel_ad<double>();

        // inform CppAD that we now may be in parallel execution mode
        sequential_execution_ = false;

        // structure used to create the threads
        pthread_t       pthread_id;
        // default for pthread_attr_setdetachstate is PTHREAD_CREATE_JOINABLE
        pthread_attr_t* no_attr= nullptr;

        // This master thread is already running, we need to create
        // num_threads - 1 more threads
        for(thread_num = 1; thread_num < num_threads; thread_num++)
        {   // Create the thread with thread number equal to thread_num
            thread_num_vptr = static_cast<void*> (
                &(thread_all_[thread_num].thread_num)
            );
            rc = pthread_create(
                    &pthread_id ,
                    no_attr     ,
                    run_one_worker,
                    thread_num_vptr
            );
            thread_all_[thread_num].pthread_id = pthread_id;
            ok &= (rc == 0);
        }

        // now call worker for the master thread
        thread_num = thread_alloc::thread_num();
        ok &= thread_num == 0;
        ok &= worker(thread_num, thread_all_[thread_num].info);

        // now wait for the other threads to finish
        for(thread_num = 1; thread_num < num_threads; thread_num++)
        {   void* no_status = nullptr;
            rc      = pthread_join(
                thread_all_[thread_num].pthread_id, &no_status
            );
            ok &= (rc == 0);
        }

        // Inform CppAD that we now are definately back to sequential mode
        sequential_execution_ = true;

        // now inform CppAD that there is only one thread
        thread_alloc::parallel_setup(1, nullptr, nullptr);
        thread_alloc::hold_memory(false);
        CppAD::parallel_ad<double>();

        // destroy the key for thread specific data
        pthread_key_delete(thread_specific_key_);

        // check to ok flag returned by during calls to work by other threads
        for(thread_num = 1; thread_num < num_threads; thread_num++)
            ok &= thread_all_[thread_num].ok;

        return ok;
    }
    // =====================================================================
    // End of General purpose code
    // =====================================================================
    // function that does the work for one thread
    bool worker(size_t thread_num, problem_specific* info)
    {   bool ok = true;

        // CppAD::vector uses the CppAD fast multi-threading allocator
        CppAD::vector< CppAD::AD<double> > ax(1), ay(1);
        ax[0] = info->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        &= CppAD::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    &= CppAD::NearEqual(d_x[0], 1., eps, eps);

        return ok;
    }
}
bool simple_ad(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 info_all
    problem_specific *info, *info_all[NUMBER_THREADS];
    for(thread_num = 0; thread_num < num_threads; thread_num++)
    {   // problem specific information
        size_t min_bytes(sizeof(info)), cap_bytes;
        void*  v_ptr = thread_alloc::get_memory(min_bytes, cap_bytes);
        info         = static_cast<problem_specific*>(v_ptr);
        info->x      = double(thread_num) + 1.;
        info_all[thread_num] = info;
    }

    ok &= run_all_workers(num_threads, info_all);

    // go down so that free memory for other threads before memory for master
    thread_num = num_threads;
    while(thread_num--)
    {   // delete problem specific information
        void* v_ptr = static_cast<void*>( info_all[thread_num] );
        thread_alloc::return_memory( v_ptr );
        // check that there is no longer any memory inuse by this thread
        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;
}