What is the garbage collection process for SplObjectStorage in PHP5?

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In PHP5, garbage collection for SplObjectStorage objects is automatic and is handled by Zend's memory manager. When an object is no longer referenced by any part of the program, it is marked as garbage and is eventually destroyed by the garbage collector. The SplObjectStorage class implements the internal SplObjectStorage::rewind() method which is used by the garbage collector to iterate over the internal object collection and clean up un-referenced objects. This method removes any objects that are no longer referenced from the internal storage of the SplObjectStorage object. In other words, the garbage collection process for SplObjectStorage in PHP5 is automatic and transparent to the developer.