There are, however, three occasions when you might use your own autorelease pools:
1. If you are writing a program that is not based on a UI framework, such as a command-line tool.
2. If you write a loop that creats many temporary objects.
3. you spawn a secondary thread.
(2) Autorelease Pools and Threads
Each thread in a Cocoa application maintains its own stack of NSAutoreleasePool objects. When a thread terminates, it automatically releases all of the autorelease pools associated with itself.
(3) ownership
* If you create an object, you own it.
* If you get an object from somewhere else, you do not own it. if you want to prevent it being disposed of, you must add yourself as an owner.
* If you are an owner of an object, you must relinquish ownership when you have finished using it.