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Fast Multi-Threading Memory Allocator: Example and Test
# include <cppad/utility/thread_alloc.hpp>
# include <vector>
# include <limits>


namespace { // Begin empty namespace



bool raw_allocate(void)
{     bool ok = true;
     using CppAD::thread_alloc;
     size_t thread;

     // check that no memory is initilaly inuse
     ok &= thread_alloc::free_all();

     // amount of static memory used by thread zero
     size_t static_inuse = 0;

     // repeatedly allocate enough memory for at least two size_t values.
     size_t min_size_t = 2;
     size_t min_bytes  = min_size_t * sizeof(size_t);
     size_t n_outter   = 10;
     size_t n_inner    = 5;
     for(size_t i = 0; i < n_outter; i++)
     {     // Do not use CppAD::vector here because its use of thread_alloc
          // complicates the inuse and avaialble results.
          std::vector<void*> v_ptr(n_inner);
          // cap_bytes will be set by get_memory
          size_t cap_bytes = 0; // set here to avoid MSC warning
          for(size_t j = 0; j < n_inner; j++)
          {     // allocate enough memory for min_size_t size_t objects
               v_ptr[j]    = thread_alloc::get_memory(min_bytes, cap_bytes);
               size_t* ptr = reinterpret_cast<size_t*>(v_ptr[j]);
               // determine the number of size_t values we have obtained
               size_t  cap_size_t = cap_bytes / sizeof(size_t);
               ok                &= min_size_t <= cap_size_t;
               // use placement new to call the size_t copy constructor
               for(size_t k = 0; k < cap_size_t; k++)
                    new(ptr + k) size_t(i + j + k);
               // check that the constructor worked
               for(size_t k = 0; k < cap_size_t; k++)
                    ok &= ptr[k] == (i + j + k);
          }
          // check that n_inner * cap_bytes are inuse and none are available
          thread = thread_alloc::thread_num();
          ok &= thread_alloc::inuse(thread) == n_inner*cap_bytes + static_inuse;
          ok &= thread_alloc::available(thread) == 0;
          // return the memrory to thread_alloc
          for(size_t j = 0; j < n_inner; j++)
               thread_alloc::return_memory(v_ptr[j]);
          // check that now n_inner * cap_bytes are now available
          // and none are in use
          ok &= thread_alloc::inuse(thread) == static_inuse;
          ok &= thread_alloc::available(thread) == n_inner * cap_bytes;
     }
     thread_alloc::free_available(thread);

     // check that the tests have not held onto memory
     ok &= thread_alloc::free_all();

     return ok;
}

class my_char {
public:
     char ch_ ;
     my_char(void) : ch_(' ')
     { }
     my_char(const my_char& my_ch) : ch_(my_ch.ch_)
     { }
};

bool type_allocate(void)
{     bool ok = true;
     using CppAD::thread_alloc;
     size_t i;

     // check initial memory values
     size_t thread = thread_alloc::thread_num();
     ok &= thread == 0;
     ok &= thread_alloc::free_all();
     size_t static_inuse = 0;

     // initial allocation of an array
     size_t  size_min  = 3;
     size_t  size_one;
     my_char *array_one  =
          thread_alloc::create_array<my_char>(size_min, size_one);

     // check the values and change them to null 'x'
     for(i = 0; i < size_one; i++)
     {     ok &= array_one[i].ch_ == ' ';
          array_one[i].ch_ = 'x';
     }

     // now create a longer array
     size_t size_two;
     my_char *array_two =
          thread_alloc::create_array<my_char>(2 * size_min, size_two);

     // check the values in array one
     for(i = 0; i < size_one; i++)
          ok &= array_one[i].ch_ == 'x';

     // check the values in array two
     for(i = 0; i < size_two; i++)
          ok &= array_two[i].ch_ == ' ';

     // check the amount of inuse and available memory
     // (an extra size_t value is used for each memory block).
     size_t check = static_inuse + sizeof(my_char)*(size_one + size_two);
     ok   &= thread_alloc::inuse(thread) - check < sizeof(my_char);
     ok   &= thread_alloc::available(thread) == 0;

     // delete the arrays
     thread_alloc::delete_array(array_one);
     thread_alloc::delete_array(array_two);
     ok   &= thread_alloc::inuse(thread) == static_inuse;
     check = sizeof(my_char)*(size_one + size_two);
     ok   &= thread_alloc::available(thread) - check < sizeof(my_char);

     // free the memory for use by this thread
     thread_alloc::free_available(thread);

     // check that the tests have not held onto memory
     ok &= thread_alloc::free_all();

     return ok;
}

} // End empty namespace

bool check_alignment(void)
{     bool ok = true;
     using CppAD::thread_alloc;

     // number of binary digits in a size_t value
     size_t n_digit = std::numeric_limits<size_t>::digits;

     // must be a multiple of 8
     ok &= (n_digit % 8) == 0;

     // number of bytes in a size_t value
     size_t n_byte  = n_digit / 8;

     // check raw allocation -------------------------------------------------
     size_t min_bytes = 1;
     size_t cap_bytes;
     void* v_ptr = thread_alloc::get_memory(min_bytes, cap_bytes);

     // convert to a size_t value
     size_t v_size_t = reinterpret_cast<size_t>(v_ptr);

     // check that it is aligned
     ok &= (v_size_t % n_byte) == 0;

     // return memory to available pool
     thread_alloc::return_memory(v_ptr);

     // check array allocation ----------------------------------------------
     size_t size_min = 1;
     size_t size_out;
     my_char *array_ptr =
          thread_alloc::create_array<my_char>(size_min, size_out);

     // convert to a size_t value
     size_t array_size_t = reinterpret_cast<size_t>(array_ptr);

     // check that it is aligned
     ok &= (array_size_t % n_byte) == 0;

     // return memory to avialable pool
     thread_alloc::delete_array(array_ptr);

     return ok;
}


bool thread_alloc(void)
{     bool ok  = true;
     using CppAD::thread_alloc;

     // check that there is only on thread
     ok  &= thread_alloc::num_threads() == 1;
     // so thread number must be zero
     ok  &= thread_alloc::thread_num() == 0;
     // and we are in sequential execution mode
     ok  &= thread_alloc::in_parallel() == false;

     // Instruct thread_alloc to hold onto memory.  This makes memory
     // allocation faster (especially when there are multiple threads).
     thread_alloc::hold_memory(true);

     // run raw allocation tests
     ok &= raw_allocate();

     // run typed allocation tests
     ok &= type_allocate();

     // check alignment
     ok &= check_alignment();

     // return allocator to its default mode
     thread_alloc::hold_memory(false);
     return ok;
}


Input File: example/utility/thread_alloc.cpp