initially: number[1] = number[2] = 0

​

thread 1                                   thread 2

//choosing[1]=true

1.tmp1 = number[1]

1.tmp2 = number[2]

                                           //choosing[2]=true

                                           2.tmp1 = number[1]

                                           2.tmp2 = number[2]

                                           number[2] = max(2.tmp1,2.tmp2)+1 = 1

                                           //choosing[2]=false

                                           //while (choosing[1]) {}

                                           while (number[1]≠0 &&

                                                  (number[1],1)<(number[2],2)) {}

                                           critical section ...

number[1] = max(1.tmp1,1.tmp2)+1 = 1

//choosing[1]=false

//while (choosing[2]) {}

while (number[2]≠0 &&

       (number[2],2)<(number[1],1)) {}

critical section ...

                                           critical section ...