Sophie: sbcl-1.0.31-1mdv2010.0 i586

sbcl-1.0.31-1mdv2010.0.i586.rpm

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<h3 class="section">7.10 Efficiency Hacks</h3>

<p>The <code>sb-ext:purify</code> function causes SBCL first to collect all
garbage, then to mark all uncollected objects as permanent, never again
attempting to collect them as garbage. This can cause a large increase
in efficiency when using a primitive garbage collector, or a more
moderate increase in efficiency when using a more sophisticated garbage
collector which is well suited to the program's memory usage pattern. It
also allows permanent code to be frozen at fixed addresses, a
precondition for using copy-on-write to share code between multiple Lisp
processes.  This is less important with modern generational garbage
collectors, but not all SBCL platforms use such a garbage collector.

   <p><a name="Function-sb_002dext_003apurify"></a>

<div class="defun">
&mdash; Function: <b>sb-ext:purify</b><var> &amp;key root-structures environment-name<a name="index-sb_002dext_003apurify-265"></a></var><br>
<blockquote><p><a name="index-sb_002dext_003apurify-266"></a>This function optimizes garbage collection by moving all currently live
   objects into non-collected storage. <code>root-structures</code> is an optional list of
   objects which should be copied first to maximize locality.

        <p><code>defstruct</code> structures defined with the (:PURE T) option are moved into
   read-only storage, further reducing <code>gc</code> cost. List and vector slots of pure
   structures are also moved into read-only storage.

        <p><code>environment-name</code> is gratuitous documentation for compacted version of the
   current global environment (as seen in <code>sb</code>!<code>c::*info-environment*</code>.) If <code>nil</code> is
   supplied, then environment compaction is inhibited.

        <p>This function is a no-op on platforms using the generational garbage
   collector (x86, x86-64, ppc). 
</p></blockquote></div>

   <p>The <code>sb-ext:truly-the</code> special form declares the type of the
result of the operations, producing its argument; the declaration is
not checked. In short: don't use it.

   <p><a name="Special_002dOperator-sb_002dext_003atruly_002dthe"></a>

<div class="defun">
&mdash; Special Operator: <b>sb-ext:truly-the</b><var> value-type form<a name="index-sb_002dext_003atruly_002dthe-267"></a></var><br>
<blockquote><p>Specifies that the values returned by <code>form</code> conform to the
<code>value-type</code>, and causes the compiler to trust this information
unconditionally.

        <p>Consequences are undefined if any result is not of the declared type
<code>--</code> typical symptoms including memory corruptions. Use with great
care. 
</p></blockquote></div>

   <p>The <code>sb-ext:freeze-type</code> declaration declares that a
type will never change, which can make type testing
(<code>typep</code>, etc.) more efficient for structure types.

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