iou: introduce iou_async() for threading

This is a preliminary implementaion of an iou-abstracted thread
pool.

Two callbacks are provided to iou_async():

async_cb:
 Called by a worker thread and must be carefully written for
 concurrent execution.

completion_cb:
 Called by iou_run() after a thread has finished with async_cb().

As completion_cb() is called in the iou_run() context, assuming
the caller is always entering iou_run() from the main thread,
it may be viewed as a continuation point for the async work
reentering the serial execution flow.

At this time every iou_new() will create two worker threads.  In
the future it may just create a thread per core or something like
that.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/iou.h b/src/iou.h
index 6609e81..77ddf97 100644
--- a/src/iou.h
+++ b/src/iou.h
@@ -36,5 +36,6 @@ int iou_run(iou_t *iou);
 int iou_quit(iou_t *iou);
 int iou_resize(iou_t *iou, unsigned entries);
 struct io_uring * iou_ring(iou_t *iou);
+int iou_async(iou_t *iou, int (*async_cb)(void *async_cb_data), void *async_cb_data, int (*completion_cb)(void *completion_cb_data), void *completion_cb_data);
 
 #endif