Thread 1 executing: start
Thread 2 executing: start
Thread 2 executing: retag x (&mut, protect)
Thread 1 executing: retag x (&mut, protect)
Thread 1 executing: retag y (&mut, protect)
Thread 2 executing: retag y (&mut, protect)
Thread 2 executing: spurious read x
Thread 1 executing: spurious read x
Thread 1 executing: ret x
Thread 2 executing: ret x
Thread 2 executing: ret y
Thread 1 executing: ret y
Thread 1 executing: write y
Thread 2 executing: write y
Thread 2 executing: end
Thread 1 executing: end