Programming :: Pthread And Mutex With Short Unlock Time?

I am wondering if pthread could make that a single thread keeps the "mutex" all the time if the time it remains unlocked is very small.

thread1
{
while (1)
{
lock; do_task(); unlock();

[code]...

I experiment the thread2 never getting access to the mutex and never printing the nice message. I would expect that once thread2 calls "lock", it would get the mutex as soon as thread1 calls unlock() but it does not seem to be the case. If I add a sleep of some microseconds (100) in thread1 after unlocking the mutex, it solves the problem.

Does anyone know if this behaviour is normal? Is there a way to configure my mutex so that thread2 receives it when unlocked?I use

pthread_mutexattr_settype(&att, PTHREAD_MUTEX_RECURSIVE_NP);
pthread_mutex_init(&handle, &att);

to create my mutex. I am running ubuntu 9.04