libgomp/doc/the-libgomp-abi/implementing-parallel-construct.rst

   1 ..
   2   Copyright 1988-2022 Free Software Foundation, Inc.
   3   This is part of the GCC manual.
   4   For copying conditions, see the copyright.rst file.
   5
   6 .. _implementing-parallel-construct:
   7
   8 Implementing PARALLEL construct
   9 *******************************
  10
  11 .. code-block:: c++
  12
  13     #pragma omp parallel
  14     {
  15       body;
  16     }
  17
  18 becomes
  19
  20 .. code-block:: c++
  21
  22     void subfunction (void *data)
  23     {
  24       use data;
  25       body;
  26     }
  27
  28     setup data;
  29     GOMP_parallel_start (subfunction, &data, num_threads);
  30     subfunction (&data);
  31     GOMP_parallel_end ();
  32
  33 .. code-block:: c++
  34
  35     void GOMP_parallel_start (void (*fn)(void *), void *data, unsigned num_threads)
  36
  37 The :samp:`{FN}` argument is the subfunction to be run in parallel.
  38
  39 The :samp:`{DATA}` argument is a pointer to a structure used to
  40 communicate data in and out of the subfunction, as discussed
  41 above with respect to FIRSTPRIVATE et al.
  42
  43 The :samp:`{NUM_THREADS}` argument is 1 if an IF clause is present
  44 and false, or the value of the NUM_THREADS clause, if
  45 present, or 0.
  46
  47 The function needs to create the appropriate number of
  48 threads and/or launch them from the dock.  It needs to
  49 create the team structure and assign team ids.
  50
  51 .. code-block:: c++
  52
  53     void GOMP_parallel_end (void)
  54
  55 Tears down the team and returns us to the previous ``omp_in_parallel()`` state.