From 757de96db5628cfbf0f2d0dbaaa135da77440bd9 Mon Sep 17 00:00:00 2001
From: Hodlinator <172445034+hodlinator@users.noreply.github.com>
Date: Fri, 21 Feb 2025 14:31:36 +0100
Subject: [PATCH] http: Ensure eventHTTP is always freed

There is a race between ThreadHTTP exiting and our queuing of the freeing-event (event_base_once).

Additional free was useful in 709 of 962 runs.
---
 src/httpserver.cpp | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/httpserver.cpp b/src/httpserver.cpp
index bc65453dbda..a3a6a8bea62 100644
--- a/src/httpserver.cpp
+++ b/src/httpserver.cpp
@@ -546,16 +546,25 @@ void StopHTTPServer()
         // Schedule a callback to call evhttp_free in the event base thread, as
         // otherwise eventHTTP often keeps internal events alive, meaning
         // aforementioned thread would never run out of events and exit.
-        event_base_once(eventBase, -1, EV_TIMEOUT, [](evutil_socket_t, short, void*) {
+        if (event_base_once(eventBase, -1, EV_TIMEOUT, [](evutil_socket_t, short, void*) {
             evhttp_free(eventHTTP);
             eventHTTP = nullptr;
-        }, nullptr, nullptr);
+        }, nullptr, nullptr) != 0) {
+            LogDebug(BCLog::HTTP, "event_base_once failed");
+        }
     }
     if (eventBase) {
         LogDebug(BCLog::HTTP, "Waiting for HTTP event thread to exit\n");
         if (g_thread_http.joinable()) g_thread_http.join();
+        if (eventHTTP) {
+            LogDebug(BCLog::HTTP, "Freeing eventHTTP-event was not picked up by ThreadHTTP before it exited.");
+            evhttp_free(eventHTTP);
+            eventHTTP = nullptr;
+        }
         event_base_free(eventBase);
         eventBase = nullptr;
+    } else {
+        Assume(!g_thread_http.joinable());
     }
     g_work_queue.reset();
     LogDebug(BCLog::HTTP, "Stopped HTTP server\n");