<indexterm><primary>parallelism</primary>
</indexterm>
- <para>GHC implements some major extensions to Haskell to support
+ <para>GHC implements some major extensions to Haskell to support
concurrent and parallel programming. Let us first establish terminology:
<itemizedlist>
<listitem><para><emphasis>Parallelism</emphasis> means running
performance. Ideally, this should be done invisibly, and with no
semantic changes.
</para></listitem>
- <listitem><para><emphasis>Concurrency</emphasis> means implementing
+ <listitem><para><emphasis>Concurrency</emphasis> means implementing
a program by using multiple I/O-performing threads. While a
- concurrent Haskell program <emphasis>can</emphasis> run on a
+ concurrent Haskell program <emphasis>can</emphasis> run on a
parallel machine, the primary goal of using concurrency is not to gain
performance, but rather because that is the simplest and most
direct way to write the program. Since the threads perform I/O,
the semantics of the program is necessarily non-deterministic.
</para></listitem>
</itemizedlist>
- GHC supports both concurrency and parallelism.
+ GHC supports both concurrency and parallelism.
</para>
<sect2 id="concurrent-haskell">
<sect2><title>Software Transactional Memory</title>
<para>GHC now supports a new way to coordinate the activities of Concurrent
- Haskell threads, called Software Transactional Memory (STM). The
+ Haskell threads, called Software Transactional Memory (STM). The
<ulink
url="http://research.microsoft.com/%7Esimonpj/papers/stm/index.htm">STM
papers</ulink> are an excellent introduction to what STM is, and how to use
it.</para>
- <para>The main library you need to use STM is <ulink
- url="../libraries/stm/Control-Concurrent-STM.html">
- Control.Concurrent.STM</ulink>. The main features supported are these:
+ <para>The main library you need to use is the <ulink
+ url="http://hackage.haskell.org/package/stm">
+ stm library</ulink>. The main features supported are these:
<itemizedlist>
<listitem><para>Atomic blocks.</para></listitem>
<listitem><para>Transactional variables.</para></listitem>
<sect2><title>Parallel Haskell</title>
<para>GHC includes support for running Haskell programs in parallel
- on symmetric, shared-memory multi-processor
+ on symmetric, shared-memory multi-processor
(SMP)<indexterm><primary>SMP</primary></indexterm>.
By default GHC runs your program on one processor; if you
want it to run in parallel you must link your program
One way to do so is forking threads using Concurrent Haskell (<xref
linkend="concurrent-haskell"/>), but the simplest mechanism for extracting parallelism from pure code is
to use the <literal>par</literal> combinator, which is closely related to (and often used
- with) <literal>seq</literal>. Both of these are available from <ulink
- url="../libraries/parallel/Control-Parallel.html"><literal>Control.Parallel</literal></ulink>:</para>
+ with) <literal>seq</literal>. Both of these are available from the <ulink
+ url="http://hackage.haskell.org/package/parallel">parallel library</ulink>:</para>
<programlisting>
infixr 0 `par`
statistics; see <xref linkend="rts-options-gc" />.</para>
<para>More sophisticated combinators for expressing parallelism are
- available from the <ulink
- url="../libraries/parallel/Control-Parallel-Strategies.html"><literal>Control.Parallel.Strategies</literal></ulink> module.
+ available from the <literal>Control.Parallel.Strategies</literal>
+ module in the <ulink
+ url="http://hackage.haskell.org/package/parallel">parallel package</ulink>.
This module builds functionality around <literal>par</literal>,
expressing more elaborate patterns of parallel computation, such as
parallel <literal>map</literal>.</para>
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