When we need to walk through a container, we use an ao2_iterator to keep track of the current position. More...

#include <astobj2.h>

Collaboration diagram for ao2_iterator:

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Data Fields
struct ao2_container *	c

int	complete

int	flags

void *	last_node

Detailed Description

When we need to walk through a container, we use an ao2_iterator to keep track of the current position.

Because the navigation is typically done without holding the lock on the container across the loop, objects can be inserted or deleted or moved while we work. As a consequence, there is no guarantee that we manage to touch all the elements in the container, and it is possible that we touch the same object multiple times.

An iterator must be first initialized with ao2_iterator_init(), then we can use o = ao2_iterator_next() to move from one element to the next. Remember that the object returned by ao2_iterator_next() has its refcount incremented, and the reference must be explicitly released when done with it.

In addition, ao2_iterator_init() will hold a reference to the container being iterated and the last container node found. These objects will be unreffed when ao2_iterator_destroy() is called to free up the resources used by the iterator (if any).

Example:

struct ao2_container *c = ... // the container we want to iterate on
struct ao2_iterator i;
struct my_obj *o;
 
i = ao2_iterator_init(c, flags);
 
while ((o = ao2_iterator_next(&i))) {
   ... do something on o ...
   ao2_ref(o, -1);
}
 
ao2_iterator_restart(&i);
while ((o = ao2_iterator_next(&i))) {
   ... do something on o ...
   ao2_ref(o, -1);
}
 
ao2_iterator_destroy(&i);

The astobj2 iterator

Note: You are not supposed to know the internals of an iterator! We would like the iterator to be opaque, unfortunately its size needs to be known if we want to store it around without too much trouble. Anyways... The iterator has a pointer to the container, and a flags field specifying various things e.g. whether the container should be locked or not while navigating on it. The iterator "points" to the current container node.

Details are in the implementation of ao2_iterator_next()