The joys of programming

The joys of programming
Nov 1st 2025, by Arisotura

There have been reports of melonDS 1.0 crashing at random when running multiple instances. This is kind of a problem, especially when local multiplayer is one of melonDS's selling points.

So I went and tried to reproduce it. I could get the 1.0 and 1.0RC builds to crash just by having two instances open, even if they weren't running anything. But I couldn't get my dev build to crash. I thought, great, one of those cursed bugs that don't manifest when you try to debug them. I think our team knows all about this.

Not having too many choices, I took the 1.0 release build and started hacking away at it with a hex editor. Basic idea being, if it crashes with no ROM loaded, the emulator core isn't the culprit, and there aren't that many places to look. So I could nop out function calls until it stopped crashing.

In the end, I ended up rediscovering a bug that I had already fixed.

The SDL joystick API isn't thread-safe. When running multiple emulator instances in 1.0, this API will get called from several different threads, since each instance gets its own emulation thread. I had already addressed this 2.5 months ago, by adding adequate locking.

I guess at the time of 1.0, it slipped through the cracks due to its random nature, as with many threading-related bugs.

Regardless, if you know your melonDS lore, you know what is coming soon. There will be a new release which will include this fix, among other fun shit. In the meantime, you can use the nightly builds.

5 comments have been posted.

< Sneak peekHappy birthday melonDS! >

lucaspltn says:
Nov 1st 2025

Programming is SO GOOD 😭😭😭😭😭

Arisotura says:
Nov 1st 2025

heh, isn't it

Heartless1Riku says:
Nov 2nd 2025

I have run into a regression while trying out nightly builds in which Pokémon ranger will not run at full speed causing audio crackle. Game works fine on the 1.0 RC though. Thank you for all your hard work.

LEGO_Vince says:
Nov 3rd 2025

I haven't been having too many issues, but I haven't been checking anything new for like a month. Hope it gets fixed.

Deaddie999 says:
Nov 6th 2025

Hey all good ! You put in such good work on MelonDS, just do your thing when you can. Ty for reviving DS Emulation.