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Mps wiki article on gc: mps formats: clarify explanation of methods, and list variants.

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@ -65,10 +65,12 @@ as:</p>
</ul>
<p>For each type of question, the client must provide a function that gives
the answer. These functions collected together are called a "format"
the answer. These functions are called "format methods", and are
collected together into a "format"
(mps_fmt_t). Usually the client developer writes these functions,
collects them into a format, and passes this format to the MPS as an
argument to mps_pool_create().</p>
calls "<code>mps_fmt_create_...</code>" to
collect them into a format, and passes this format to the MPS as an
argument to <code>mps_pool_create()</code>.</p>
<p>A client's format code is 'special'. It is called at special times (eg.
when handling an interrupt), and is quite restricted in what it is
@ -108,41 +110,61 @@ whether it is a client object, a forwarding object, or a padding object.
<h3><a id="format-methods">The most important format methods are:</a></h3>
<p>To support collectable client objects:</p>
<p>Indicate the size of a collectable client object:</p>
<ul>
<li> Skip (see <a href="../reference/index.html#mps_fmt_skip_t">mps_fmt_skip_t</a>):
tell the MPS how big this object is.</li>
client must tell the MPS how big this object is.</li>
</ul>
<p>To support movable client objects:</p>
<p>List all references from this object to (other) collectable objects:</p>
<ul>
<li> Scan (see <a href="../reference/index.html#mps_fmt_scan_t">mps_fmt_scan_t</a>):
tell the MPS what other objects this object
refers to;</li>
<li> Copy (see <a href="../reference/index.html#mps_fmt_copy_t">mps_fmt_copy_t</a>):
copy an object to a new location.</li>
client must 'scan' the object for pointers, and tell
the MPS to 'fix' each pointer it finds;</li>
</ul>
<p>To support forwarding objects (once a movable client object has been moved):</p>
<p>Move this client object:</p>
<ul>
<li> Copy (see <a href="../reference/index.html#mps_fmt_copy_t">mps_fmt_copy_t</a>):
client must copy the object to a new location.</li>
</ul>
<p>Create/use a forwarding object (used by an incremental moving collector after moving a client object):</p>
<ul>
<li> Fwd (see <a href="../reference/index.html#mps_fmt_fwd_t">mps_fmt_fwd_t</a>):
create a forwarding object here, please;</li>
client must create a forwarding object here, and store
the supplied forwarding pointer in it;</li>
<li> IsFwd (see <a href="../reference/index.html#mps_fmt_isfwd_t">mps_fmt_isfwd_t</a>):
is this a forwarding object, and where
did it move to?</li>
client must test whether this is a forwarding object
(created by the Fwd method), and if so return the
forwarding pointer stored in it. (This is how the
MPS remembers where a moved object was moved to).</li>
</ul>
<p>To support padding objects:</p>
<p>Create a padding object:</p>
<ul>
<li> Pad (see <a href="../reference/index.html#mps_fmt_pad_t">mps_fmt_pad_t</a>):
create a padding object here, please.</li>
</ul>
<h3><a id="format-variants">Format Variants</a></h3>
<p>There are several different ways to package-up the format methods -- these different ways are called 'variants'. MPS currently supports four format variants. The creation functions for these are:</p>
<ul>
<li> <a href="../reference/index.html#mps_fmt_create_A">mps_fmt_create_A</a>;</li>
<li> <a href="../reference/index.html#mps_fmt_create_B">mps_fmt_create_B</a>;</li>
<li> <a href="../reference/index.html#mps_fmt_create_auto_header">mps_fmt_create_auto_header</a>;</li>
<li> <a href="../reference/index.html#mps_fmt_create_fixed">mps_fmt_create_fixed</a>.</li>
</ul>
<p>It's a bit messy -- sorry.</p>
<h2><a id="section-B" name="section-B">B. Document History</a></h2>
<pre>
2006-06-02 RHSK Created.
2006-06-02 RHSK Introduction to MPS Formats
2006-06-06 RHSK Formats: clarify explanation of methods, and list variants.
</pre>