core: simplify background IO API

- removes unused "completed" IO callback handler
- moves primary post-IO callback handlers from the queue definition to
  the actual IO objects.
- allows IO object callbacks to be handled generically instead of based
  on the queue they were submitted from.

1 files changed, 4 insertions, 1 deletions

diff --git a/proxy.h b/proxy.h
index f82630b..dce74f5 100644
--- a/proxy.h
+++ b/proxy.h
@@ -409,7 +409,10 @@ struct _io_pending_proxy_t {
     int io_queue_type;
     LIBEVENT_THREAD *thread;
     conn *c;
-    mc_resp *resp;  // original struct ends here
+    mc_resp *resp;
+    io_queue_cb return_cb; // called on worker thread.
+    io_queue_cb finalize_cb; // called back on the worker thread.
+    // original struct ends here
 
     struct _io_pending_proxy_t *next; // stack for IO submission
     STAILQ_ENTRY(_io_pending_proxy_t) io_next; // stack for backends