Cómo detectar errores de sincronización con synccheck

A __syncthreads barrier only works if every thread in the block reaches it. Skip it for some threads and behavior turns undefined. ⚠️

Calling a barrier inside a branch some threads skip is a divergent sync, the exact hazard the synccheck tool is built to catch.

Run the synccheck tool of compute-sanitizer to detect illegal or divergent uses of __syncthreads and related barriers.

Here only some threads call the barrier, leaving the rest behind. synccheck flags this as a divergent __syncthreads.

Pull the barrier out of the branch so all threads reach it together, while only the guarded work stays conditional.

Every thread must run the same number of barriers, so a loop with a thread-dependent trip count plus an inner sync is a trap.

A thread that hits an early return before a barrier never arrives, so synccheck reports the remaining threads stuck waiting.

synccheck names the barrier and the threads that diverged, so you can trace which branch or return broke the contract.

synccheck also checks __syncwarp masks, flagging when a thread participates with a mask that does not match its lane.

Compile with -lineinfo so synccheck can point at the exact barrier call instead of just naming the kernel.

Run synccheck on its own pass, separate from memcheck and racecheck, since each sanitizer tool targets a different class of bug.

What problem does the synccheck tool specifically detect?

You learned the barrier contract, ran synccheck, and fixed divergent syncs by moving barriers out of branches. Your block stays in step. 🙌