Free public beta until December 4, 2026:
every course is open, no card needed.
After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept.
How the beta works
thread dump
A list of every thread in a running JVM with its state, stack and locks.
Produced by jcmd Thread.print, jstack , Ctrl+Break (Windows) or kill -3 (macOS, Linux); it lists locked and waiting-to-lock monitors and ends with any "Found one Java-level deadlock" report.