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team_bthread.cpp

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# include <boost/thread.hpp>
# include <cppad/cppad.hpp>
# include "../team_thread.hpp"
# define MAX_NUMBER_THREADS 48

namespace {
    using CppAD::thread_alloc;

    // number of threads in the team
    size_t num_threads_ = 1;

    // no need to cleanup up thread specific data
    void cleanup(size_t*)
    {   return; }

    // thread specific pointer the thread number (initialize as null)
    boost::thread_specific_ptr<size_t> thread_num_ptr_(cleanup);

    // type of the job currently being done by each thread
    enum thread_job_t { init_enum, work_enum, join_enum } thread_job_;

    // barrier used to wait for other threads to finish work
    boost::barrier* wait_for_work_ = nullptr;

    // barrier used to wait for master thread to set next job
    boost::barrier* wait_for_job_ = nullptr;

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

    // structure with information for one thread
    typedef struct {
        // The thread
        boost::thread*       bthread;
        // CppAD thread number as global (pointed to by thread_num_ptr_)
        size_t               thread_num;
        // true if no error for this thread, false otherwise.
        bool                 ok;
    } thread_one_t;

    // vector with information for all threads
    thread_one_t thread_all_[MAX_NUMBER_THREADS];

    // pointer to function that does the work for one thread
    void (* worker_)(void) = nullptr;

    // ---------------------------------------------------------------------
    // in_parallel()
    bool in_parallel(void)
    {   return ! sequential_execution_; }

    // ---------------------------------------------------------------------
    // thread_number()
    size_t thread_number(void)
    {   // return thread_all_[thread_num].thread_num
        return *thread_num_ptr_.get();
    }
    // --------------------------------------------------------------------
    // function that gets called by boost thread constructor
    void thread_work(size_t thread_num)
    {   bool ok = wait_for_work_ != nullptr;
        ok     &= wait_for_job_  != nullptr;
        ok     &= thread_num     != 0;

        // thread specific storage of thread number for this thread
        thread_num_ptr_.reset(& thread_all_[thread_num].thread_num );

        while( true )
        {
            // Use wait_for_jog_ to give master time in sequential mode
            // (so it can change global information like thread_job_)
            wait_for_job_->wait();

            // case where we are terminating this thread (no more work)
            if( thread_job_ == join_enum)
                break;

            // only other case once wait_for_job_ has been completed (so far)
            ok &= thread_job_ == work_enum;
            worker_();

            // Use wait_for_work_ to inform master that our work is done and
            // that this thread will not use global infromation until
            // passing its barrier wait_for_job_ above.
            wait_for_work_->wait();

        }
        thread_all_[thread_num].ok &= ok;
        return;
    }
}

bool team_create(size_t num_threads)
{   bool ok = true;;

    if( num_threads > MAX_NUMBER_THREADS )
    {   std::cerr << "team_create: num_threads greater than ";
        std::cerr << MAX_NUMBER_THREADS << std::endl;
        exit(1);
    }
    // check that we currently do not have multiple threads running
    ok  = num_threads_ == 1;
    ok &= wait_for_work_ == nullptr;
    ok &= wait_for_job_  == nullptr;
    ok &= sequential_execution_;

    size_t thread_num;
    for(thread_num = 0; thread_num < num_threads; thread_num++)
    {   // Each thread gets a pointer to its version of this thread_num
        // so it knows which section of thread_all it is working with
        thread_all_[thread_num].thread_num = thread_num;

        // initialize
        thread_all_[thread_num].ok = true;
        thread_all_[0].bthread     = nullptr;
    }
    // Finish setup of thread_all_ for this thread
    thread_num_ptr_.reset(& thread_all_[0].thread_num);

    // Now that thread_number() has necessary information for the case
    // num_threads_ == 1, 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>();

    // now change num_threads_ to its final value.
    num_threads_ = num_threads;

    // initialize two barriers, one for work done, one for new job ready
    wait_for_work_ = new boost::barrier( (unsigned int) num_threads );
    wait_for_job_  = new boost::barrier( (unsigned int) num_threads );

    // initial job for the threads
    thread_job_           = init_enum;
    if( num_threads > 1 )
        sequential_execution_ = false;

    // 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_all_[thread_num].bthread =
            new boost::thread(thread_work, thread_num);
    }

    // Current state is other threads are at wait_for_job_.
    // This master thread (thread zero) has not completed wait_for_job_
    sequential_execution_ = true;
    return ok;
}

bool team_work(void worker(void))
{
    // Current state is other threads are at wait_for_job_.
    // This master thread (thread zero) has not completed wait_for_job_
    bool ok = sequential_execution_;
    ok     &= thread_number() == 0;
    ok     &= wait_for_work_  != nullptr;
    ok     &= wait_for_job_   != nullptr;

    // set global version of this work routine
    worker_ = worker;

    // set the new job that other threads are waiting for
    thread_job_ = work_enum;

    // Enter parallel exectuion when master thread calls wait_for_job_
    if( num_threads_ > 1 )
        sequential_execution_ = false;
    wait_for_job_->wait();

    // Now do the work in this thread and then wait
    // until all threads have completed wait_for_work_
    worker();
    wait_for_work_->wait();

    // Current state is other threads are at wait_for_job_.
    // This master thread (thread zero) has not completed wait_for_job_
    sequential_execution_ = true;

    size_t thread_num;
    for(thread_num = 0; thread_num < num_threads_; thread_num++)
        ok &= thread_all_[thread_num].ok;
    return ok;
}

bool team_destroy(void)
{   // Current state is other threads are at wait_for_job_.
    // This master thread (thread zero) has not completed wait_for_job_
    bool ok = sequential_execution_;
    ok     &= thread_number() == 0;
    ok     &= wait_for_work_ != nullptr;
    ok     &= wait_for_job_  != nullptr;

    // set the new job that other threads are waiting for
    thread_job_ = join_enum;

    // enter parallel exectuion soon as master thread completes wait_for_job_
    if( num_threads_ > 1 )
            sequential_execution_ = false;
    wait_for_job_->wait();

    // now wait for the other threads to be destroyed
    size_t thread_num;
    ok &= thread_all_[0].bthread == nullptr;
    for(thread_num = 1; thread_num < num_threads_; thread_num++)
    {   thread_all_[thread_num].bthread->join();
        delete thread_all_[thread_num].bthread;
        thread_all_[thread_num].bthread = nullptr;
    }
    // now we are down to just the master thread (thread zero)
    sequential_execution_ = true;

    // destroy wait_for_work_
    delete wait_for_work_;
    wait_for_work_ = nullptr;

    // destroy wait_for_job_
    delete wait_for_job_;
    wait_for_job_ = nullptr;

    // check ok before changing num_threads_
    for(thread_num = 0; thread_num < num_threads_; thread_num++)
        ok &= thread_all_[thread_num].ok;

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

    return ok;
}

const char* team_name(void)
{   return "bthread"; }