More Semaphores in Redcode

While not as elegant as the solution found by Neo and Roy, the following has the advantage of only requiring one DAT.

semaphore: dat    1
        ....
reset:     mul.ab semaphore, semaphore
wait:      djn    reset,     semaphore
           mov.a  #0,        semaphore
        ....
signal:    mov    #1,        }sema

The second technique kills waiting processes, then respawns them when signaled.

semaphore: dat    1
        ....
kill:      dat    0
        ....
wait:      djn    kill,      semaphore
next:
        ....
signal:    mov.a  #1,        semaphore
           add.x  semaphore, semaphore
           seq.a  #1,        semaphore
           spl    next

Semaphores in Redcode

I'm looking for suggestions on how to code busy-waiting semaphores in Redcode.  The lack of an atomic test-and-set operation complicates matters.

The code below works for up to three processes, but under certain circumstances can fail with four processes.  The entry points are wait and signal.

semaphore: dat 1
        ....
fail:      add #1,   semaphore
wait:      djn fail, semaphore
        .....
signal:    add #1,   semaphore

If you have any suggestions, please let me know in the comments below.