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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>GSCache class documentation</title>
</head>
<body>
<font face="serif">
<h1><a name="title$GSCache">GSCache class documentation</a></h1>
<h3>Authors</h3>
<dl>
<dt>Richard Frith-Macdonald (<a href="mailto:rfm@gnu.org"><code>rfm@gnu.org</code></a>)</dt>
<dd>
</dd>
</dl>
<p><b>Version:</b> 36997</p>
<p><b>Date:</b> 2013-08-21 09:47:28 +0100 (Wed, 21 Aug 2013)</p>
<p><b>Copyright:</b> (C) 2005 Free Software Foundation, Inc.</p>
<div>
<hr width="50%" align="left" />
<h3>Contents -</h3>
<ol>
<li>
<a href="#001000000000">Software documentation for the GSCache class</a>
</li>
<li>
<a href="#002000000000">Software documentation for the
NSObject(GSCacheSizeInBytes)
category</a>
</li>
<li>
<a href="#003000000000">Software documentation for the GSCacheDelegate
protocol</a>
</li>
</ol>
<hr width="50%" align="left" />
</div>
<h1><a name="001000000000">
Software documentation for the GSCache class
</a></h1>
<h2><a name="class$GSCache">GSCache</a> : NSObject</h2>
<blockquote class="declared">
<dl>
<dt><b>Declared in:</b></dt>
<dd>GSCache.h</dd>
</dl>
</blockquote>
<div class="desc">
The GSCache class is used to maintain a cache of objects
in memory for relatively rapid access. <br /> Typical
usage might be to keep the results of a database query
around for a while in order to re-use them... for
instance when application configuration is obtained
from a database which might be updated while the
application is running. <br /> When the cache is
full, old objects are removed to make room for new ones
on a least-recently-used basis. <br /> Cache sizes may be
limited by the number of objects in the cache, or by
the memory used by the cache, or both. Calculation of the
size of items in the cache is relatively expensive, so
caches are only limited by number of objects in the
default case. <br /> Objects stored in the cache may
be given a limited lifetime, in which case an attempt to
fetch an <em>expired</em> object from the cache will
cause it to be removed from the cache instead (subject
to control by the delegate). <br /> Cache keys may be
objects of any type as <strong>long</strong> as they
are copyable (and the copied keys are immutable) and
implement the
-hash
and -isEqual:
methods such that any two keys can be tested for
equality and used as dictionary keys. <br /> NB.
GSCache currently does not support subclassing... use
it as is or extend it via categories, but do not try to
add instance variables.
</div>
<b>Method summary</b>
<ul>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache+allInstances">+allInstances</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache+description">+description</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-currentObjects">-currentObjects</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-currentSize">-currentSize</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-delegate">-delegate</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-description">-description</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-lifetime">-lifetime</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-maxObjects">-maxObjects</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-maxSize">-maxSize</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-name">-name</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-objectForKey$">-objectForKey:</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-purge">-purge</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-setDelegate$">-setDelegate:</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-setLifetime$">-setLifetime:</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-setMaxObjects$">-setMaxObjects:</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-setMaxSize$">-setMaxSize:</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-setName$">-setName:</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-setObject$forKey$">-setObject:forKey:</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-setObject$forKey$lifetime$">-setObject:forKey:lifetime:</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-setObject$forKey$until$">-setObject:forKey:until:</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$GSCache-shrinkObjects$andSize$">-shrinkObjects:andSize:</a></li>
</ul>
<hr width="50%" align="left" />
<div class="method">
<h3><a name="method$GSCache+allInstances">allInstances </a></h3>
+ (NSArray*) <b>allInstances</b>;<br />
<div class="desc">
Return all the current cache instances... useful if
you want to do something to all cache instances in your
process.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache+description">description </a></h3>
+ (NSString*) <b>description</b>;<br />
<div class="desc">
Return a report on all GSCache instances... calls
the
<a rel="gsdoc" href="#method$GSCache-description">
[GSCache -description]
</a>
method of the individual cache instances to get a
report on each one.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-currentObjects">currentObjects </a></h3>
- (unsigned) <b>currentObjects</b>;<br />
<div class="desc">
Return the count of objects currently in the cache.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-currentSize">currentSize </a></h3>
- (<a rel="gsdoc" href="GSLinkedList.html#type$NSUInteger">NSUInteger</a>) <b>currentSize</b>;<br />
<div class="desc">
Return the total size of the objects currently in
the cache.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-delegate">delegate </a></h3>
- (id) <b>delegate</b>;<br />
<div class="desc">
Return the delegate object previously set using the
<a rel="gsdoc" href="#method$GSCache-setDelegate$">
-setDelegate:
</a>
method.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-description">description </a></h3>
- (NSString*) <b>description</b>;<br />
<div class="desc">
Returns a string describing the status of the
receiver for debug/reporting.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-lifetime">lifetime </a></h3>
- (unsigned) <b>lifetime</b>;<br />
<div class="desc">
Return the default lifetime for items set in the
cache. <br /> A value of zero means that items are
not purged based on lifetime.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-maxObjects">maxObjects </a></h3>
- (unsigned) <b>maxObjects</b>;<br />
<div class="desc">
Return the maximum number of items in the cache.
<br /> A value of zero means there is no limit.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-maxSize">maxSize </a></h3>
- (<a rel="gsdoc" href="GSLinkedList.html#type$NSUInteger">NSUInteger</a>) <b>maxSize</b>;<br />
<div class="desc">
Return the maximum tital size of items in the cache.
<br /> A value of zero means there is no limit.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-name">name </a></h3>
- (NSString*) <b>name</b>;<br />
<div class="desc">
Return the name of this instance (as set using
-setName:)
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-objectForKey$">objectForKey: </a></h3>
- (id) <b>objectForKey:</b> (id)aKey;<br />
<div class="desc">
Return the cached value for the specified key, or
<code>nil</code> if there is no value in the cache.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-purge">purge </a></h3>
- (void) <b>purge</b>;<br />
<div class="desc">
Remove all items whose lifetimes have passed (if
lifetimes are in use for the cache). <br />
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-setDelegate$">setDelegate: </a></h3>
- (void) <b>setDelegate:</b> (id)anObject;<br />
<div class="desc">
Sets the delegate for the receiver. <br /> The
delegate object is not retained. <br /> If a
delegate it set, it will be sent the messages in
the (GSCacheDelegate) protocol (if it implements them
... which it does not need to do).
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-setLifetime$">setLifetime: </a></h3>
- (void) <b>setLifetime:</b> (unsigned)max;<br />
<div class="desc">
Sets the lifetime (seconds) for items added to the
cache. If this is set to zero then items are not
removed from the cache based on lifetimes when the
cache is full and an object is added, though
<em>expired</em> items are still removed when an
attempt to retrieve them is made.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-setMaxObjects$">setMaxObjects: </a></h3>
- (void) <b>setMaxObjects:</b> (unsigned)max;<br />
<div class="desc">
Sets the maximum number of objects in the cache. If
this is non-zero then an attempt to set an object in a
full cache will result in the least recently used item
in the cache being removed.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-setMaxSize$">setMaxSize: </a></h3>
- (void) <b>setMaxSize:</b> (<a rel="gsdoc" href="GSLinkedList.html#type$NSUInteger">NSUInteger</a>)max;<br />
<div class="desc">
Sets the maximum total size for objects in the cache.
If this is non-zero then an attempt to set an object
whose size would exceed the cache limit will result
in the least recently used items in the cache being
removed.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-setName$">setName: </a></h3>
- (void) <b>setName:</b> (NSString*)name;<br />
<div class="desc">
Sets the <var>name</var> of this instance.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-setObject$forKey$">setObject: forKey: </a></h3>
- (void) <b>setObject:</b> (id)anObject<b> forKey:</b> (id)aKey;<br />
<div class="desc">
Sets (or replaces)the cached value for the specified
key. <br /> The value of <var>anObject</var> may be
<code>nil</code> to remove any cached object for
<var>aKey</var>.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-setObject$forKey$lifetime$">setObject: forKey: lifetime: </a></h3>
- (void) <b>setObject:</b> (id)anObject<b> forKey:</b> (id)aKey<b> lifetime:</b> (unsigned)lifetime;<br />
<div class="desc">
Sets (or replaces)the cached value for the specified
key, giving the value the specified
<var>lifetime</var> (in seconds). A
<var>lifetime</var> of zero means that the item is
not limited by <var>lifetime</var>. <br /> The value of
<var>anObject</var> may be <code>nil</code> to remove
any cached object for <var>aKey</var>.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-setObject$forKey$until$">setObject: forKey: until: </a></h3>
- (void) <b>setObject:</b> (id)anObject<b> forKey:</b> (id)aKey<b> until:</b> (NSDate*)expires;<br />
<div class="desc">
Sets (or replaces)the cached value for the specified
key, giving the value the specified expiry date. Calls
<a rel="gsdoc" href="#method$GSCache-setObject$forKey$lifetime$">
-setObject:forKey:lifetime:
</a>
to do the real work... this is just a convenience method
to handle working out the lifetime in seconds. <br /> If
<var>expires</var> is <code>nil</code> or not in the
future, this method simply removes the cache entry
for <var>aKey</var>. If it is many years in the future,
the item is set in the cache so that it is not limited
by lifetime.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$GSCache-shrinkObjects$andSize$">shrinkObjects: andSize: </a></h3>
- (void) <b>shrinkObjects:</b> (unsigned)objects<b> andSize:</b> (<a rel="gsdoc" href="GSLinkedList.html#type$NSUInteger">NSUInteger</a>)size;<br />
<div class="desc">
Called by
<a rel="gsdoc" href="#method$GSCache-setObject$forKey$lifetime$">
-setObject:forKey:lifetime:
</a>
to make space for a new object in the cache (also when
the cache is resized). <br /> This will, if a lifetime
is set (see the
<a rel="gsdoc" href="#method$GSCache-setLifetime$">
-setLifetime:
</a>
method) first purge all <em>expired</em>
<var>objects</var> from the cache, then (if
necessary) remove <var>objects</var> from the
cache until the number of <var>objects</var> and
<var>size</var> of cache meet the limits specified.
<br /> If the <var>objects</var> argument is zero
then all <var>objects</var> are removed from the
cache. <br /> The <var>size</var> argument is used
<em>only</em> if a maximum <var>size</var> is set for
the cache.
</div>
<hr width="25%" align="left" />
</div>
<h1><a name="002000000000">
Software documentation for the
NSObject(GSCacheSizeInBytes)
category
</a></h1>
<h2>NSObject(<a name="category$NSObject(GSCacheSizeInBytes)">GSCacheSizeInBytes</a>)</h2>
<blockquote class="declared">
<dl>
<dt><b>Declared in:</b></dt>
<dd>GSCache.h</dd>
</dl>
</blockquote>
<div class="desc">
</p>
<p>
This category declares the
<a rel="gsdoc" href="#method$NSObject(GSCacheSizeInBytes)-sizeInBytes$">
-sizeInBytes:
</a>
method which is used by
<a rel="gsdoc" href="#class$GSCache">GSCache</a>
to ask objects for their size when adding them to a
cache which has a limited size in bytes.
</p>
<p>
</p>
<p>
The
NSObject
implementation of this method is
intended to provide a rough estimnate of
object size which subclasses may refine in order
to provide more accurate sizing information. <br />
Subclasses should call the superclass
implementation and use the resulting
size information (if it is zero then the object is
in the exclude set and the subclass implementation
should also return zero) as a starting point on
which to add the sizes of any objects contained.
</p>
<p>
For example:
<pre>
- (NSUInteger) sizeInBytes: (NSMutableSet*)exclude
{
NSUInteger size = [super sizeInBytes: exclude];
if (size > 0)
{
size += [myInstanceVariable sizeInBytes: exclude];
}
return size;
}
</pre>
</p>
<p>
The performance library contains implementations giving
reasonable size estimates for several common
classes:
</p>
<p>
<ul>
<li>
NSArray
</li>
<li>
NSData
</li>
<li>
NSDictionary
</li>
<li>
NSSet
</li>
<li>
NSString
</li>
<li>
GSMimeDocument (if built with the GNUstep
base library)
</li>
</ul>
</p>
<p>
The default
NSObject
) implementation provides a reasonable size for any
class whose instance variables do not include other
objects or pointers to memory allocated on the
heap.
</p>
<p>
</div>
<b>Method summary</b>
<ul>
<li><a rel="gsdoc" href="GSCache.html#method$NSObject(GSCacheSizeInBytes)-sizeInBytes$">-sizeInBytes:</a></li>
</ul>
<hr width="50%" align="left" />
<div class="method">
<h3><a name="method$NSObject(GSCacheSizeInBytes)-sizeInBytes$">sizeInBytes: </a></h3>
- (<a rel="gsdoc" href="GSLinkedList.html#type$NSUInteger">NSUInteger</a>) <b>sizeInBytes:</b> (NSMutableSet*)exclude;<br />
<div class="desc">
If the receiver is a member of the <var>exclude</var>
set, this method simply returns zero. Otherwise, the
receiver adds itsself to the <var>exclude</var>
set and returns its own size in bytes (the size of the
memory used to hold all the instance variables
defined for the receiver's class including all
superclasses).
</div>
<hr width="25%" align="left" />
</div>
<h1><a name="003000000000">
Software documentation for the GSCacheDelegate
protocol
</a></h1>
<h2><a name="protocol$(GSCacheDelegate)">GSCacheDelegate</a></h2>
<blockquote class="declared">
<dl>
<dt><b>Declared in:</b></dt>
<dd>GSCache.h</dd>
</dl>
</blockquote>
<div class="desc">
This protocol defines the messages which may be sent to
a delegate of a GSCache object. The messages are only sent
if the delegate actually implements them, so a delegate
does not need to actually conform to the protocol.
</div>
<b>Method summary</b>
<ul>
<li><a rel="gsdoc" href="GSCache.html#method$(GSCacheDelegate)-mayRefreshItem$withKey$lifetime$after$">-mayRefreshItem:withKey:lifetime:after:</a></li>
<li><a rel="gsdoc" href="GSCache.html#method$(GSCacheDelegate)-shouldKeepItem$withKey$lifetime$after$">-shouldKeepItem:withKey:lifetime:after:</a></li>
</ul>
<hr width="50%" align="left" />
<div class="method">
<h3><a name="method$(GSCacheDelegate)-mayRefreshItem$withKey$lifetime$after$">mayRefreshItem: withKey: lifetime: after: </a></h3>
- (void) <b>mayRefreshItem:</b> (id)anObject<b> withKey:</b> (id)aKey<b> lifetime:</b> (unsigned)lifetime<b> after:</b> (unsigned)delay;<br />
<div class="desc">
Alerts the delegate to the fact that
<var>anObject</var>, which was cached using
<var>aKey</var> and will expire <var>delay</var>
seconds in the future has been looked up now, and
needs to be refreshed if it is not to expire from the
cache. <br /> This is called the first time an
attempt is made to access the cached value for
<var>aKey</var> and the object is found in the cache
but more than half its <var>lifetime</var> has expired.
<br /> The delegate method (if implemented) may
replace the item in the cache immediately, or do it
later asynchronously, or may simply take no action.
</div>
<hr width="25%" align="left" />
</div>
<div class="method">
<h3><a name="method$(GSCacheDelegate)-shouldKeepItem$withKey$lifetime$after$">shouldKeepItem: withKey: lifetime: after: </a></h3>
- (BOOL) <b>shouldKeepItem:</b> (id)anObject<b> withKey:</b> (id)aKey<b> lifetime:</b> (unsigned)lifetime<b> after:</b> (unsigned)delay;<br />
<div class="desc">
Asks the delegate to decide whether
<var>anObject</var>, which was cached using
<var>aKey</var> and expired <var>delay</var> seconds
ago should still be retained in the cache. <br /> This
is called when an attempt is made to access the cached
value for <var>aKey</var> and the object is found in
the cache but it is no longer valid (has expired).
<br /> If the method returns <code>YES</code>, then
<var>anObject</var> will not be removed as it
normally would. This allows the delegate to change
the cached item or refresh it. <br /> For instance, the
delegate could replace the object in the cache
before returning <code>YES</code> in order to update
the cached value when its <var>lifetime</var> has
expired. <br /> Another possibility would be for
the delegate to return <code>YES</code> (in order to
continue using the existing object) and queue an
asynchronous database query to update the
cache later. In this case the expiry time of the item
will be reset relative to the current time, based upon
its original <var>lifetime</var>.
</div>
<hr width="25%" align="left" />
</div>
<br />
</font>
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