Question

There are so many functions like

1. NSDefaultMallocZone()
2. NSCreateZone();
3. NSRecycleZone();
4. NSSetZoneName();
5. NSZoneMalloc();
and many more related to NSZone

What does NSZone means, where to use these functions and when?
What are the advantages of initWithZone: and how to use in my iphone app?

Answer 1

NSZone is Apple’s way of optimizing
object allocation and freeing. NSZone
is not an object; it is an opaque
C-struct storing information about how
memory should be handled for a set of
objects.

One rarely needs to worry about
handling your own zones in
applications; Cocoa handles it
transparently. A default NSZone is
created on startup and all objects
default to being allocated there. So
why would you want to use your own?

If you are mass-allocating hundreds of
cheap objects, you may find the cost
of actually allocating space for them
becomes significant. Because the
standard zone is used all the time, it
can become very patchy; deleted
objects can leave awkward gaps
throughout memory. The allocator for
the standard NSZone knows this, and it
tries to fill these gaps in preference
to grabbing more memory off the
system, but this can be costly in time
if the zone has grown quite large.

If you want to mass-allocate objects,
then, you can create your own zone and
tell it not to bother with finding
gaps to put new objects in. The
allocator can now jump to the end of
its allotted memory each time and
quickly assign memory to your new
objects, saving a lot of effort.

Allocators can save you time
elsewhere, too, as asking the OS for
more memory, which a zone needs to do
whenever it fills up, is another
costly operation if it’s done a lot.
Much quicker is to ask for huge chunks
of memory at a time, and you can tell
your NSZone what to do here as well.

Rumor has it that NSZone could save
you deallocation time in the Good Old
Days, too, with a method that simply
chucks away all the allotted memory
without bothering to call
deallocators. If a set of objects is
self-contained, this could save a lot
of time, as you can chuck them all
away at once without tediously
deallocating them all. Alas, there
appears to be no sign of this godsend
in the current documentation; the
single NSZone method (NSRecycleZone?)
carefully puts all the objects in a
zone neatly on the default NSZone. Not
exactly a huge time-saver.

So, in summary, zones save you time in
mass allocations. But only if
programmers know how to use them!

From CocoaDev

Edit from comments: "Also important to note is that you can’t use NSZone any more if you’re using ARC. Which you should be."