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 has problems with
passing objects from one scope to another, so it's
augmented 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 -
Methods whose names begin with init return an
initialised version of the receiving object,
owned by the caller. NB. The returned object
may not actually be the same as the receiver...
sometimes an init method releases the original
receiver and returns an alternative.
Adds anObj 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).
Allocate and return an autorelease pool instance.
If there is an already-allocated
NSAutoreleasePool available, save time by
just returning that, rather than allocating a new one.
The pool instance becomes the current
autorelease pool for this thread.
Intended to trigger a garbage collection run (if
needed) when called in a garbage collected
environment. In a non-garbage collected
environment, this method implements the
undocumented MacOS-X behavior, and releases
the receiver.
Empties the current pool by releasing all the
autoreleased objects in it. Also destroys any
child pools (ones created after the receiver in the
same thread) causing any objects in those pools to be
released. This is a low cost (efficient)
method which may be used to get rid of autoreleased
objects in the pool, but carry on using the pool.
Warning the underscore at the start of the
name of this instance variable indicates that, even
though it is not technically private, it is
intended for internal use within the package, and
you should not use the variable in other code.
Warning the underscore at the start of the
name of this instance variable indicates that, even
though it is not technically private, it is
intended for internal use within the package, and
you should not use the variable in other code.
Warning the underscore at the start of the
name of this instance variable indicates that, even
though it is not technically private, it is
intended for internal use within the package, and
you should not use the variable in other code.
Warning the underscore at the start of the
name of this instance variable indicates that, even
though it is not technically private, it is
intended for internal use within the package, and
you should not use the variable in other code.
Warning the underscore at the start of the
name of this instance variable indicates that, even
though it is not technically private, it is
intended for internal use within the package, and
you should not use the variable in other code.
Warning the underscore at the start of the
name of this instance variable indicates that, even
though it is not technically private, it is
intended for internal use within the package, and
you should not use the variable in other code.