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000bf4a523
git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/performance/trunk@37812 72102866-910b-0410-8b05-ffd578937521
80 lines
3.2 KiB
Objective-C
80 lines
3.2 KiB
Objective-C
#if !defined(INCLUDED_GSUNIQUED)
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#define INCLUDED_GSUNIQUED 1
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/**
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Copyright (C) 2014 Free Software Foundation, Inc.
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Written by: Richard Frith-Macdonald <rfm@gnu.org>
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Date: April 2014
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This file is part of the Performance Library.
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 3 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the Free
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Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111 USA.
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*/
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#import <Foundation/NSObject.h>
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/** Class used to unique other objects.<br />
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* <p>The point of this class is to lower the memory footprint and speed
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* up comparisons (pointer equality) in cases where an application
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* stores multiple copies of the same object in various maps.<br />
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* Since uniquing is performed by storing an immutable copy of the
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* original object in a map until there are no further references
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* to that object, it's pointless to use this uniquing unless the
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* application would be storing at least two copies of the object.<br />
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* Also, since this is thread-safe there is a lock management
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* overhead wherever a uniqued object is released, so performance
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* gains are to be expected only if the uniqued object has a
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* relatively long lifetime and is tested for equality with other
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* instances frequently.<br />
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* In short, use with care; while uniquing can have a big performance
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* advantage for some programs, this is actually quite rare.
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* </p>
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* <p>The internal implementation of the uniquing works by taking
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* immutable copies of the objects to be uniqued, storing those copies
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* in a hash table, and swizzling their class pointers to a sub-class
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* which will automatically remove the instance from the hash table
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* before it is deallocated.<br />
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* Access to the hash table is protected by locks so that uniqued
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* objects may be used freely in multiple threads.<br />
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* The name of the subclass used is the name of the original class
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* with 'GSUniqued' added as a prefix.
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* </p>
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*/
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@interface GSUniqued : NSObject
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/** This method returns a copy of its argument, uniqued so that other
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* such copies of equal objects will be the same instance.<br />
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* The argument must respond to -copyWithZone: by returning an instance
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* of class of immutable objects (ie where the -hash and -isEqual:
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* methods are stable for that instance).
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*/
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+ (id) copyUniqued: (id<NSObject,NSCopying>)anObject;
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@end
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/** Category for uniquing any copyable object.<br />
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* NB. This must only be used by classes for which -copyWithZone:
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* produces an instance of an immutable class.
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*/
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@interface NSObject (GSUniqued)
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/** This method returns a copy of the receiver uniqued so that other
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* such copies of equal objects content will be the same instance.
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*/
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- (id) copyUniqued;
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@end
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#endif
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