question about homework in chapter30 threads-cv

[tangxibomb]

homework 4, run ./main-two-cvs-while -p 1 -c 3 -m 1 -C 0,0,0,1,0,0,0:0,0,0,1,0,0,0:0,0,0,1,0,0,0 -l 10 -v -t

the output is

NF         P0 C0 C1 C2 
  0 [*--- ] p0
  0 [*--- ]    c0
  0 [*--- ]       c0
  0 [*--- ]          c0
  0 [*--- ]       c1
  0 [*--- ]       c2
  0 [*--- ]    c1
  0 [*--- ]    c2
.....

It seems that thread c1 execute Mutex_lock(&m);while (num_full == 0) {,so thread c1 get the lock.

Then the CPU run thread c0,want to execute the same code.when he run Mutex_lock(&m); ,the lock is owned by c1.So he won't return from this routine.But the output shows that thread c0 has executed the Mutex_lock(&m);while (num_full == 0) {.

WHY?
I have a poor english.I 'll be appreciated if someone can answer me!