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NSAutoreleasePool class reference

Authors

Andrew Kachites McCallum (mccallum@gnu.ai.mit.edu)
Richard Frith-Macdonald (rfm@gnu.org)

Version: 1.52

Date: 2003/07/31 23:49:31

Copyright: (C) 1995, 1996, 1997 Free Software Foundation, Inc.

Software documentation for the NSAutoreleasePool class

NSAutoreleasePool : NSObject

Declared in:
Foundation/NSAutoreleasePool.h
Standards:

The standard OpenStep system of memory management employs retain counts. When an object is created, it has a retain count of 1. When an object is retained, the retain count is incremented. When it is released the retain count is decremented, and when the retain count goes to zero the object gets deallocated.

A simple retain/release mechanism is not very interesting ... so it's spiced up with autorelease pools. You can use the AUTORELEASE() macro to call the [NSObject -autorelease] method, which adds an object to the current autorelease pool by calling [NSAutoreleasePool +addObject:] .
An autorelease pool simply maintains a reference to each object added to it, and for each addition, the autorelease pool will call the [NSObject -release] method of the object when the pool is released. So doing an AUTORELEASE() is just the same as doing a RELEASE() , but deferred until the current autorelease pool is deallocated.

The NSAutoreleasePool class maintains a separate stack of autorelease pools objects in each thread.

When an autorelease pool is created, it is automatically added to the stack of pools in the thread.

When a pool is destroyed, it (and any pool later in the stack) is removed from the stack.

This mechanism provides a simple but controllable and reasonably efficient way of managing temporary objects. An object can be autoreleased and then passed around and used until the topmost pool in the stack is destroyed.

Most methods return objects which are either owned by autorelease pools or by the receiver of the method, so the lifetime of the returned object can be assumed to be the shorter of the lifetime of the current autorelease pool, or that of the receiver on which the method was called.
The exceptions to this are those object returned by -

[NSObject +alloc] , [NSObject +allocWithZone:]
Methods whose names begin with alloc return an uninitialised object, owned by the caller.
[NSObject -init]
Methods whose names begin with init return an initialised version of the receiving object, owned by the caller.
NB. The returned object may not actualy be the same as the receiver... sometimes an init method releases the original receiver and returns an alternative.
[NSObject +new]
Methods whose names begin with new combine the effects of allocation and initialisation.
[NSObject -copy] , [<NSCopying>-copyWithZone:]
Methods whose names begin with copy create a copy of the receiver which is owned by the caller.
[NSObject -mutableCopy] , [<NSMutableCopying>-mutableCopyWithZone:]
Methods whose names begin with mutableCopy create a copy of the receiver which is owned by the caller.

Method summary

_endThread:

+ (void) _endThread: (NSThread*)thread;

Warning the underscore at the start of the name of this method indicates that it is private, for internal use only, and you should not use the method in your code.
Destroys all the autorelease pools in the thread. You should not call this directly, it's called automatically when a thread exits.


addObject:

+ (void) addObject: (id)anObj;

Adds the specified object to the current autorelease pool. If there is no autorelease pool in the thread, a warning is logged and the object is leaked (ie it will not be released).


autoreleaseCountForObject:

+ (unsigned) autoreleaseCountForObject: (id)anObject;

Counts the number of times that the specified object occurs in autorelease pools in the current thread.

This method is slow and should probably only be used for debugging purposes.


enableRelease:

+ (void) enableRelease: (BOOL)enable;

Specifies whether objects contained in autorelease pools are to be released when the pools are deallocated (by default YES ).

You can set this to NO for debugging purposes.


freeCache

+ (void) freeCache;

When autorelease pools are deallocated, the memory they used is retained in a cache for re-use so that new polls can be created very quickly.

This method may be used to empty that cache, ensuring that the minimum memory is used by the application.


resetTotalAutoreleasedObjects

+ (void) resetTotalAutoreleasedObjects;

Resets (to zero) the count of autoreleased objects in the current thread.


setPoolCountThreshhold:

+ (void) setPoolCountThreshhold: (unsigned)c;

Specifies a limit to the number of objects that may be added to an autorelease pool. When this limit is reached an exception is raised.

You can set this to a smallish value to catch problems with code that autoreleases too many objects to operate efficiently.

Default value is maxint.


totalAutoreleasedObjects

+ (unsigned) totalAutoreleasedObjects;

Returns the number of objects which have been autoreleased in the current thread since the last call to +resetTotalAutoreleasedObjects .
NB. This is not normally supported... enable it as a compile time option by editing NSAutoreleasePool.m when building the base library.


addObject:

- (void) addObject: (id)anObj;

Adds the specified object to this autorelease pool.



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