From 8fbd087ba9599eee3f392fb9f066fd563ec4b55a Mon Sep 17 00:00:00 2001
From: Michael McGee <mmcgee@jumptrading.com>
Date: Sat, 9 Nov 2024 20:23:32 +0000
Subject: [PATCH] gui: fix rare crash

---
 src/disco/gui/fd_gui.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/src/disco/gui/fd_gui.c b/src/disco/gui/fd_gui.c
index 421615ab0..476f59289 100644
--- a/src/disco/gui/fd_gui.c
+++ b/src/disco/gui/fd_gui.c
@@ -1402,10 +1402,15 @@ fd_gui_handle_optimistically_confirmed_slot( fd_gui_t * gui,
     for( ulong i=gui->summary.slot_optimistically_confirmed; i>=_slot; i-- ) {
       fd_gui_slot_t * slot = gui->slots[ i % FD_GUI_SLOTS_CNT ];
       if( FD_UNLIKELY( slot->slot==ULONG_MAX ) ) break;
-      FD_TEST( slot->slot==i );
-      slot->level = FD_GUI_SLOT_LEVEL_COMPLETED;
-      fd_gui_printf_slot( gui, i );
-      fd_http_server_ws_broadcast( gui->http );
+      if( FD_LIKELY( slot->slot==i ) ) {
+        /* It's possible for the optimistically confirmed slot to skip
+           backwards between two slots that we haven't yet replayed.  In
+           that case we don't need to change anything, since they will
+           get marked properly when they get completed. */
+        slot->level = FD_GUI_SLOT_LEVEL_COMPLETED;
+        fd_gui_printf_slot( gui, i );
+        fd_http_server_ws_broadcast( gui->http );
+      }
     }
   }