获得pthread锁的优先级

Question

Let say i have a list List and i have pthread_t t1 that polls from the list and i have many other pthreads that insert elements to the list. The list is locked with a lock listLock . when t1 has the lock - if the list is empty he goes to sleep with pthread_cond_wait(..) and when a thread inserts to the list he signals him.

my question is: if t1 is in wait state and there are many threads that are stuck in pthread_mutex_lock(&listLock) , when the lock will be unlocked, will t1 have a priority to get the lock or will he "fight" the other threads to get the lock?

thank you

Answer 1

It will fight, however it's a fair fight. All callers are put into a queue based on the order that they called the wait. It's completely deterministic.

However given the way that you're using things, you may possibly want to think about using a read/write lock. It allows N simultaneous readers, but anytime something tries to do a write it will lock everyone down until it's done.

Answer 2

As Chris said, the threads will fairly fight for the mutex. However, you may control how fair is the scheduling of the threads by using threads attribute variables. The following two links you guide you in the advantages and drawbacks of using this mechanism.

Thread Scheduling with pthreads under Linux and FreeBSD

Basic Scheduling Functions