From c3ce3f160671de4b8172f765a7c42e40d1956af6 Mon Sep 17 00:00:00 2001
From: Jakub <106778416+MarekZegare4@users.noreply.github.com>
Date: Thu, 3 Sep 2026 22:34:47 +0200
Subject: [PATCH] fix(sim): add sim_stop_main_loop() -- host pages must stop
 old instances

A Reset control on a host page (meshcore-solo-site's RESET button,
mesh.html's own Reset buttons) re-invokes the MODULARIZE factory for the
same simInstanceTag to simulate a device restart, since board.reboot()
just exit()s the wasm process (inert / freezes the tab under
-sEXIT_RUNTIME=0). Nothing ever tore down the OLD instance's own
emscripten_set_main_loop() callback, so it keeps ticking forever after
being "replaced" -- and keeps drawing onto the same simInstanceTag-keyed
<canvas> the new instance draws onto too. Two visible symptoms this
caused on meshcore-solo-site: flicker/reversion after resetting the same
device more than once (multiple orphaned instances competing for one
canvas), and -- together with the HomeScreen::poll() fix in 5fbfd7c5 --
would have still left a residual single-old-instance repaint race even
after that fix alone.

sim_stop_main_loop() wraps emscripten_cancel_main_loop() so a host page
can explicitly stop the OLD Module reference right before discarding it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018iubftDmKNWmkNnhJRz8UH
---
 examples/companion_radio/main.cpp | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/examples/companion_radio/main.cpp b/examples/companion_radio/main.cpp
index 2e9d9d37..b12f931f 100644
--- a/examples/companion_radio/main.cpp
+++ b/examples/companion_radio/main.cpp
@@ -359,6 +359,27 @@ extern "C" EMSCRIPTEN_KEEPALIVE int sim_is_ready() {
   return g_sim_ready ? 1 : 0;
 }
 
+// A host page's "Reset" control (meshcore-solo-site's RESET button,
+// mesh.html's own Reset buttons) re-invokes the MODULARIZE factory
+// function for the same simInstanceTag to simulate a real device restart
+// -- board.reboot() is inert here (exit()s the whole wasm process, which
+// under -sEXIT_RUNTIME=0 just freezes the tab). That leaves the OLD
+// Module instance's own emscripten_set_main_loop() callback (see
+// sim_main.cpp's sim_idbfs_ready()) still registered and still ticking
+// forever afterwards -- nothing ever tore it down. Two real, user-visible
+// consequences: it keeps re-drawing onto the same simInstanceTag-keyed
+// <canvas> element the NEW instance is also drawing onto (visible as
+// flicker/reversion once more than one reset has piled up orphaned
+// instances), and if the old instance had been sitting on the Shutdown
+// screen, HomeScreen::poll() keeps re-firing shutdown() -> turnOff() on
+// every tick, permanently blacking that canvas out from under the new
+// instance. A host page should call this on the OLD Module reference
+// right before discarding it (i.e. right before re-invoking the
+// MODULARIZE factory for that same tag) to actually stop it.
+extern "C" EMSCRIPTEN_KEEPALIVE void sim_stop_main_loop() {
+  emscripten_cancel_main_loop();
+}
+
 extern "C" EMSCRIPTEN_KEEPALIVE int sim_test_advert_flood() {
   if (!g_sim_ready) return 0;
   return the_mesh.advertFlood() ? 1 : 0;