cond_signal wakes an arbitrary thread that's waiting on the argument, not the thread specified by the argument.

If you wanted to use cond_signal, you'd have to replace

        cond_wait ($baton) until $baton == $id;
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with

        for (;;) {
           cond_wait ($baton);
           last if $baton == $id;
           # This isn't the right sprinter, so try another.
           cond_signal ($baton);
        }
[download]

I don't know which approach is better.