conditional - Output for sample code for an upcoming exam concerning pthread -

pthread_mutex_t mutex = pthread_mutex_initializer;  pthread_cond_t cond = pthread_cond_initializer;  int token = 2;  int value = 3;  void * red ( void *arg ) {   int myid = * ((int *) arg);   pthread_mutex_lock( &mutex );   while ( myid != token) {   pthread_cond_wait( &cond, &mutex );   }   value = value + (myid + 3);   printf( "red: id %d \n", value);   token = (token + 1) % 3;   pthread_cond_broadcast( &cond );   pthread_mutex_unlock( &mutex );  }  void * blue ( void *arg ) {   int myid = * ((int *) arg);   pthread_mutex_lock( &mutex );   while ( myid != token) {   pthread_cond_wait( &cond, &mutex );   }   value = value * (myid + 2);   printf( "blue: id %d \n", value);   token = (token + 1) % 3;   pthread_cond_broadcast( &cond );   pthread_mutex_unlock( &mutex );  }  void * white ( void *arg ) {   int myid = * ((int *) arg);   pthread_mutex_lock( &mutex );   while ( myid != token) {   pthread_cond_wait( &cond, &mutex );   }   value = value * (myid + 1);   printf( "white: id %d \n", value);   token = (token + 1) % 3;   pthread_cond_broadcast( &cond );   pthread_mutex_unlock( &mutex );  }   main( int argc, char *argv[] ) {   pthread_t tid;   int count = 0;   int id1, id2, id3;   id1 = count;   n = pthread_create( &tid, null, red, &id1);   id2 = ++count;   n = pthread_create( &tid, null, blue, &id2);   id3 = ++count;   n = pthread_create( &tid, null, white, &id3);   if ( n = pthread_join( tid, null ) ) {   fprintf( stderr, "pthread_join: %s\n", strerror( n ) );   exit( 1 );   }  } 

i looking comments , or notes output be. exam , offered example. not homework or going used type of submission. looking understand going on. appreciated.

i'm going assume know function of locks, condition variables, , waits. have 3 threads each call red, blue, , white. token 2, , value 3.

red called when id1 = 0, stay in while block calling wait() until token = 0.

blue called when id3 = 1, , stay in while block called wait() until token 1.

white called when id2 = 2, , stay in while block calling wait() until token 2.

so white enter critical section first, since it's 1 won't enter while loop. value = 3 * ( 3 ) = 9; token = ( 3 ) % 3 = 0;

broadcast wakes every waiting thread, 1 enter critical section red. adds 3 value 12; token = ( 1 ) % 3 = 1; broadcast wakes blue.

blue enters critical section. value = 12 * 3; token = 2 ( doesn't matter anymore ).

this order of threads execute, assume test asking. however, should come out just:

white 9

this because there 1 pthread_t tid. after pthread_join( tid, null ), can exit. if put different pthread_t in each of pthread_create() of them print.