Threads, Events, Mailboxes, and Semaphores

Run several testbench activities in parallel and choose the right synchronization mechanism.

Several activities at once

A testbench often needs to generate commands, monitor responses, and enforce a timeout in parallel. fork...join launches several threads.

fork
  drive_requests();
  monitor_responses();
  watch_timeout();
join

join waits for every thread. join_any resumes after the first finishes. join_none resumes immediately and leaves all branches running. With join_any, the remaining branches often need a clean stop such as disable fork so a timeout or driver does not outlive the test.

Automatic local variables prevent loop iterations from unintentionally sharing one value between threads.

for (int port = 0; port < 4; port++) begin
  automatic int selected_port