From 08654a9a86831147a496681f25187a0a0dd78b18 Mon Sep 17 00:00:00 2001
From: ADAM David Alan Martin <adam@recursive.engineer>
Date: Sat, 6 Jan 2024 01:46:34 -0500
Subject: [PATCH] Deal with last-item-in-the-queue bug.

---
 Atomic/Dropbox.h | 27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/Atomic/Dropbox.h b/Atomic/Dropbox.h
index 312fddb..68c4ff1 100644
--- a/Atomic/Dropbox.h
+++ b/Atomic/Dropbox.h
@@ -102,12 +102,21 @@ namespace Alepha::Hydrogen::Atomic  ::detail::  Dropbox_m
 				drops.producer.releaseBox();
 			}
 
+			void
+			recycle()
+			{
+				auto &filled= drops.consumer.acquireBox();
+				filled.notification= nullptr;
+				filled.items.clear();
+				drops.consumer.releaseBox();
+			}
+
 		public:
 			explicit
 			Dropbox( const size_t lim )
 				: boxLimit( lim )
 			{
-				drops.consumer.releaseBox();
+				recycle();
 			}
 
 			Item
@@ -118,14 +127,24 @@ namespace Alepha::Hydrogen::Atomic  ::detail::  Dropbox_m
 				{
 					[[unlikely]];
 					auto notification= std::move( filled.notification );
-					filled.notification= nullptr;
-					drops.consumer.releaseBox();
+					recycle();
 					std::rethrow_exception( std::move( notification ) );
 				}
+				assert( not filled.items.empty() );
 				auto &rv= *filled.pos++;
+				// If it was the last item and we're going to rotate/reccyle,
+				// be sure that we don't reference the now-stale value.
+				// This is a special case that will only come up at the end of each queue
+				// cycle.
+				//
+				// I need to research if NRV applies in this circumstance -- if so, then the
+				// `rv` variable can be an instance instead of a reference.
 				if( filled.pos == end( filled.items ) and filled.notification == nullptr )
 				{
-					drops.consumer.releaseBox();
+					[[unlikely]];
+					auto rvTemp= std::move( rv );
+					recycle();
+					return rvTemp;
 				}
 				return std::move( rv );
 			}