Multicores
==========

Since computers with multiple cores are the norm today,
let us discuss how this can be exploited with D.

While concurrency and parallelism are
`actually different concepts <http://stackoverflow.com/questions/1050222/concurrency-vs-parallelism-what-is-the-difference>`_,
we will not discuss them separately,
because programmers usually encounter them at same time anyways.
However, this means we only provide an overview here.

Threads
-------

The basic mechanism for threads managed by the operating system
(PThread) is provided by ``std.concurrency``.

.. literalinclude:: ../examplecode/threads.d
   :language: d

Once you use threads,
keep in mind that in D global variables are thread-local.
You can declare them global to the whole process with the ``shared`` qualifier.

.. code-block:: d

   shared int countA;  // global counter
   int countB;         // thread-local counter

Tasks
-----

This is about the lightweight thread variant,
which is managed by the program itself.
It is also called user-level threads.
Since the tasks are usually executed by a thread pool,
they are run in parallel as well.

.. literalinclude:: ../examplecode/tasks.d
   :language: d

Synchronization
---------------

Once you have parallelism,
usually concurrency arises and the need for synchronization.
Of course,
D provides the ususal suspects:
Locks,
semaphores,
atomic variables.

Memory Model
------------