Parallel Programming with O2scl
===============================

:ref:`O2scl <o2scl>`

Parallel contents
-----------------

- :ref:`Thread safety and parallelism`
- :ref:`OpenMP and O2scl`
- :ref:`MPI and O2scl`

Thread safety and parallelism
-----------------------------

Generally, O₂scl objects are thread-safe in the same way that
classes like ``std::vector<double>`` are thread-safe:
reads are safe and writes are unsafe. It may be useful to make
objects ``const`` to ensure that one is reading data in a
thread-safe way. O₂scl is designed to ensure const methods are
thread-safe, unless noted. (A few classes contain mutable internal
members which mean that const methods are not thread-safe, and
this is noted in the class documentation.)

OpenMP and O2scl
----------------

OpenMP support may be enabled during installation by
``--enable-openmp``. OpenMP support during installation
allows O₂scl to use parallelism to speed up
some :ref:`table <table>` functions and to 
test the multithreaded behavior of :ref:`anneal_para <anneal_para>`,
:ref:`mcmc_para_base <mcmc_para_base>`, and :ref:`mcmc_para_table
<mcmc_para_table>`.

On some systems, code similar to the following may be required to
ensure that the error handler is valid on each OpenMP thread::
  
  int main(int argc, char *argv[]) {
    cout.setf(ios::scientific);
    MPI_Init(&argc,&argv);
    // Create a new error handler for this thread
    o2scl::err_hnd_cpp ee;
    o2scl::err_hnd=&ee;
    // Do stuff here
    MPI_Finalize();
    return 0;
  }

You can test to see if OpenMP support was enabled during installation
in the :cpp:var:`o2scl::o2scl_settings` object of type
:ref:`lib_settings_class <lib_settings_class>` or with ``acol -v``.

MPI and O2scl
-------------

Currently, all MPI calls are in header classes. MPI functions are used
in :ref:`anneal_para <anneal_para>`, :ref:`mcmc_para_base
<mcmc_para_base>`, and :ref:`mcmc_para_table <mcmc_para_table>`.
An MPI-friendly tool for seeding random number generators is
provided in :cpp:func:`o2scl::rng_set_seed_mpi()`.
    
.. You can test to see if MPI support was enabled during installation in
   the \ref o2scl::o2scl_settings object of type \ref
   o2scl::lib_settings_class or with ``acol -v``.