Asynchronous content switching

1. A method comprising:

receiving a first signal from a user session;

creating a first ranked list of content items;

based on the first signal, assigning a first subset of the first ranked list to a first plurality of slots of the user session;

assigning a second subset of the first ranked list to a second plurality of slots of the user session;

the second subset does not include the first subset;

the second plurality of slots does not include the first plurality of slots;

receiving at least one second signal from the user session;

the at least one second signal comprises user activity data associated with a rendering of the first subset in the first plurality of slots;

receiving at least one third signal from the user session;

the at least one third signal comprises position context data associated with the rendering of the first subset in the first plurality of slots;

based on the user activity data and the position context data, creating a second ranked list of content items asynchronously with the receiving of the at least one second signal from the user session;

the second ranked list does not include the first subset; and

assigning the second ranked list instead of the second subset to the second plurality of slots.

2. The method of claim 1 , wherein creating the second ranked list comprises:

computing a probability of user response to a content item not in the first subset based on the user activity data, the position context data, and content item data associated with the position context data; and

determining the second ranked list based on the computed probability.

3. The method of claim 1 , further comprising:

creating the first ranked list using a first ranking mechanism that does not include user activity data generated after the receiving of the first signal or position context data generated after the receiving of the first signal.

4. The method of claim 1 , further comprising:

receiving a fourth signal from the user session; and

based on the fourth signal, rendering the second ranked list instead of the second subset in the second plurality of slots.

5. The method of claim 1 , further comprising:

for a content item of the second ranked list, determining whether a distribution criterion is satisfied; and

in response to determining that the distribution criterion is not satisfied, assigning the content item to a slot of the second plurality of slots.

6. The method of claim 1 , further comprising:

applying an auction process to a position of a slot in the second plurality of slots; and

based on an output of the auction process, assigning a content item of the second ranked list to the slot.

7. The method of claim 1 , wherein creating the second ranked list comprises:

retrieving a content item from a set of content items that does not include the first subset and does not include the second subset; and

based on the user activity data and the position context data, replacing a content item of the second subset with the retrieved content item.

8. The method of claim 1 , wherein creating the second ranked list comprises:

dividing the second ranked list into a plurality of groups; and

based on at least one of the user activity data or the position context data, re-ranking at least one group of the plurality of groups at least once before the at least one group is rendered.

9. The method of claim 1 , further comprising:

storing a content item rendered in the first subset in a rendered cache; and

removing the content item stored in the rendered cache from the second ranked list.

10. The method of claim 1 , further comprising:

computing a first score for a first content item of the second subset;

computing a second score for a second content item retrieved from a set of content items that does not include the first subset or the second subset;

determining whether a difference between the first score and the second score satisfies a ranking criterion; and

in response to determining that the difference between the first score and the second score satisfies the ranking criterion, including the second content item in the second ranked list instead of the first content item.

11. The method of claim 1 , further comprising:

storing the second subset and position context data associated with the second subset in a cache;

reading the position context data from the cache; and

creating the second ranked list using the position context data read from the cache.

12. The method of claim 11 , further comprising:

receiving a fourth signal from the user session;

determining that the fourth signal comprises a pagination mechanism; and

rendering the second ranked list instead of the second subset in the second plurality of slots.

13. A system comprising:

at least one processor; and

at least one memory coupled to the at least one processor;

the at least one memory comprising instructions that when executed by the at least one processor cause the at least one processor to be capable of:

creating a first ranked list of content items;

assigning a first subset of the first ranked list to a first set of slots of a user session;

assigning a second subset of the first ranked list to a second set of slots having lower positions than the first set of slots in the user session;

receiving user activity data and corresponding slot position context data from the user session;

using the received user activity and corresponding slot position context data, creating a second ranked list of content items from the second subset and a set of content items that does not include the first ranked list;

assigning the second ranked list instead of the second subset to the second set of slots; and

continuously re-creating the second ranked list asynchronously while receiving signals from the user session.

14. The system of claim 13 , wherein the instructions, when executed by the at least one processor, cause the at least one processor to be capable of:

computing a probability of user response to a content item not in the first subset based on the user activity data, the slot position context data, and content item data associated with the slot position context data; and

determining the second ranked list based on the computed probability.

15. The system of claim 13 , wherein the instructions, when executed by the at least one processor, cause the at least one processor to be capable of:

for a content item of the second ranked list, determining whether a distribution criterion is satisfied; and

in response to determining that the distribution criterion is not satisfied, assigning the content item to a slot of the second set of slots.

16. The system of claim 13 , wherein the instructions, when executed by the at least one processor, cause the at least one processor to be capable of:

applying an auction process to a position of a slot in the second set of slots; and

based on an output of the auction process, assigning a content item of the second ranked list to the slot.

17. The system of claim 13 , wherein the instructions, when executed by the at least one processor, cause the at least one processor to be capable of:

retrieving a content item from a set of content items that does not include the first subset and does not include the second subset; and

based on the user activity data and the slot position context data, replacing a content item of the second subset with the retrieved content item.

18. The system of claim 13 , wherein the instructions, when executed by the at least one processor, cause the at least one processor to be capable of:

determining whether a comparison of at least one content item of the second ranked list to at least one content item of the first ranked list satisfies a similarity criterion; and

in response to determining that the comparison satisfies the similarity criterion, removing at least one content item from the second ranked list.