Crash Reporting for Games With Hot Reload Enabled

Hot reload is one of the best things you can add to an iteration loop, letting you patch code or scripts while the game keeps running and your level stays loaded. It is also a reliable source of crashes that no player will ever see but that will eat your afternoon, because the running process now holds state created by one version of the code while executing another. This post is about making those crashes legible: capturing what survived a reload, recognizing faults that the reload itself caused, and instrumenting your handler so a trace tells you whether you found a real bug or a reload artifact.

Why hot reload creates its own crashes

When you swap code at runtime, the live process keeps every object, allocation, and pointer it had a moment ago, but the meaning of that memory just changed. A struct that grew a field now has stale instances laid out the old way. A function pointer cached before the reload points into a module that no longer exists. A virtual table moved. None of this happens in a clean build because the program starts from a consistent state, which is exactly why these crashes feel mysterious and why they vanish the moment you restart.

The category to internalize is the layout mismatch. As long as the code you reload only changes logic, you are usually fine. The instant it changes a data structure that already has live instances, you have objects whose bytes mean one thing and whose code expects another. Crashes from this are often delayed: the reload succeeds, play continues, and a fault surfaces three minutes later when something touches a stale object. Without reload history in the report, that delay makes the cause invisible.

Capturing state that survives a reload

The whole point of hot reload is that game state persists, so your crash reporting has to treat that persistent state as a first-class suspect. Record a small reload log in memory: how many reloads have happened this session, what was reloaded each time, and a timestamp. Keep it in a region that the reload mechanism explicitly preserves, the same way you preserve the game world, so it survives into the new code and rides along into any crash report that follows.

When a crash fires, attach that log. A trace that points at an object accessor is ambiguous on its own, but the same trace with three recent script reloads in the last ninety seconds tells you to suspect a layout mismatch before you suspect your logic. The reload log turns a confusing intermittent fault into a clear hypothesis, and it costs almost nothing to maintain because you are only appending a line each time a reload occurs.

Crashes triggered by the reload itself

Some faults happen during the reload, not after it. The swap touches global initializers, re-registers callbacks, and rebinds whatever your engine wired to the old module. If a destructor runs against the wrong layout or a registration list still references a freed function, the crash lands squarely inside the reload machinery. These are the ones that scare developers off hot reload entirely, and they deserve their own bucket in your reporting so you can see how often the mechanism rather than the gameplay is at fault.

Wrap the reload operation so you know, at crash time, whether you were mid-reload. A simple in-progress flag set before the swap and cleared after lets your handler tag the report accordingly. A crash with that flag set is a reload-machinery bug; a crash with it clear but recent reloads logged is a post-reload state bug. Separating these two cleanly is most of the diagnostic battle, because they have entirely different fixes.

Keeping traces honest after a swap

A stack trace captured after a hot reload can lie if your symbol resolution uses the old module image. The addresses in the live process now belong to freshly loaded code, so resolving them against a stale symbol set produces frames that look plausible and point at the wrong function. Make sure your handler resolves against the currently loaded module, and record which version of each reloadable unit was live when the crash occurred so offline resolution uses the right symbols.

Version your reloadable units. Each script bundle or shared library that can be swapped gets an identifier that you bump on every reload, and that identifier goes into the crash report. Now a trace is anchored to a specific revision of the code that was actually running, not to whatever happens to be on disk when you investigate. This matters most for the delayed crashes, where the offending reload may be several swaps in the past.

Setting it up with Bugnet

Bugnet captures crashes with stack traces and device context, and the reload history fits naturally as custom fields: reload count this session, last reloaded unit, and the in-progress flag. Because the in-game report button also captures game state automatically, a tester who hits a glitch after a reload but not a hard crash can still file a report that carries the same reload context, which is often where these bugs first show up. You end up with one record that says what was running and how it got there.

Occurrence grouping is unusually valuable here because reload bugs repeat in tight loops while you iterate. Folding twenty identical post-reload faults into one issue with a count keeps your dashboard readable during a heavy iteration session. Filter by the reload-in-progress field to separate machinery crashes from state crashes instantly, and sort by occurrence to find the swap that hurts most. The context travels with every report, so you are never guessing whether a given trace came from a clean run or a hot-patched one.

Iterate fast without losing the thread

Hot reload is worth the trouble, and the trouble shrinks once your reporting distinguishes its failure modes. Make the reload log and version identifiers part of the reload system itself so every swap updates them automatically and every crash inherits the context. Treat a report tagged reload-in-progress as a bug in your tooling and a report with recent reloads but no flag as a layout or lifetime bug, and you will fix both kinds far faster than by staring at traces.

Build the habit of reproducing on a clean start. If a crash vanishes when you restart and replay without reloading, you have confirmed it is a reload artifact, which narrows the fix to lifetime and layout handling rather than gameplay logic. Keep that loop tight, keep the reload context flowing into every report, and hot reload stays the productivity win it should be instead of a source of crashes you cannot explain.

A crash after a hot reload is usually a stale object, not a logic bug. Carry the reload history into every report and the cause stops hiding.