Deadlock Empire
Schedule threads step by step to break concurrent code
In The Deadlock Empire you play the scheduler, not the programmer. Each level shows a few threads running short pieces of C# code. You choose which thread runs its next instruction, one step at a time. Your goal is to break the program, for example by getting two threads into the same critical section or causing a deadlock.
Free · No login · Browser · Intermediate
About Deadlock Empire
The levels show how locks, monitors and other synchronization tools fail when code is not careful. It suits developers who are learning concurrency, and university courses use it as an exercise.
It runs in the browser with no sign-up, and you can undo steps and retry. Petr Hudeček and Michal Pokorný made it at HackCambridge 2016. The code is open source under the GPL v2.
On Breakpoint since 23 Oct 2026.