Software Locking (with hardware support)

Notes

• This is 6.5
  • Mutex locks - mutual exclusion locks.
• Hardware locks are hard to use, especially in multi processor/core systems.
• So multiple software solutions are built on top.
• mutex locks have essentually two methods
  • Acquire the lock
  • Release the lock.
• Acquire should be written such that it is blocking until the process is safe to enter the critical section.
• In linux mutex is accomplished with
  • The pthred_mutex routines.
  • int pthread_mutex_lock(pthread_mutex_t *mutex);
  • int pthread_mutex_trylock(pthread_mutex_t *mutex);
  • int pthread_mutex_unlock(pthread_mutex_t *mutex);
• These routines have a large range of behaviours
  • We will only look at the process version, not the thread version.
  • And this means a more complex setup stage.
• We need some shared memory, in this case we will use anonomous shared memory.
• Take a look at mutex.cpp.