IMPORTANT: This project was completed by Matt Thomas. You may still contact the people above for details, but please do not submit an application for this project.
This project proposal is a subtask of smp networking and is elegible for funding independently.
The goal of this project is to implement lockess and atomic producer/consumer queues (PCQs) in the kernel. A PCQ allows multiple writers (producers) but only a single reader (consumer). Compare-And-Store operations are used to allow lockless updates. The consumer is expected to be protected by a mutex that covers the structure that the PCQ is embedded into (e.g. socket lock, ifnet hwlock). These queues operate in a First-In, First-Out (FIFO) manner. The act of inserting or removing an item from a PCQ does not modify the item in any way. A PCQ does not prevent an item being inserted multiple times into a single PCQ.
Since this structure is not specific to networking it has to be accessed
via <sys/pcq.h> and the code has to live in kern/subr_pcq.c.
The proposed interface looks like this:
bool pcq_put(pcq_t *pcq, void *item);Places item at the end of the queue. If there is no room in the queue for the item, false is returned; otherwise true is returned. The item must not have the value
NULL.void *pcq_peek(pcq_t *pcq);Returns the next item to be consumed from the queue but does not remove it from the queue. If the queue is empty,
NULLis returned.void *pcq_get(pcq_t *pcq);Removes the next item to be consumed from the queue and returns it. If the queue is empty,
NULLis returned.size_t pcq_maxitems(pcq_t *pcq);Returns the maximum number of items that the queue can store at any one time.
pcq_t *pcq_create(size_t maxlen, km_flags_t kmflags);void pcq_destroy(pcq_t *pcq);