Improve ilist.h's support for deletion of slist elements during iteration.

Previously one had to use slist_delete(), implying an additional scan of
the list, making this infrastructure considerably less efficient than
traditional Lists when deletion of element(s) in a long list is needed.
Modify the slist_foreach_modify() macro to support deleting the current
element in O(1) time, by keeping a "prev" pointer in addition to "cur"
and "next".  Although this makes iteration with this macro a bit slower,
no real harm is done, since in any scenario where you're not going to
delete the current list element you might as well just use slist_foreach
instead.  Improve the comments about when to use each macro.

Back-patch to 9.3 so that we'll have consistent semantics in all branches
that provide ilist.h.  Note this is an ABI break for callers of
slist_foreach_modify().

Andres Freund and Tom Lane

1 files changed, 1 insertions, 1 deletions

diff --git a/src/include/postmaster/bgworker_internals.h b/src/include/postmaster/bgworker_internals.h
index 6484cfb7a6..478a1fff0d 100644
--- a/src/include/postmaster/bgworker_internals.h
+++ b/src/include/postmaster/bgworker_internals.h
@@ -39,7 +39,7 @@ extern slist_head BackgroundWorkerList;
 extern Size BackgroundWorkerShmemSize(void);
 extern void BackgroundWorkerShmemInit(void);
 extern void BackgroundWorkerStateChange(void);
-extern void ForgetBackgroundWorker(RegisteredBgWorker *);
+extern void ForgetBackgroundWorker(slist_mutable_iter *cur);
 
 #ifdef EXEC_BACKEND
 extern BackgroundWorker *BackgroundWorkerEntry(int slotno);