/* A counting semaphore. */
struct semaphore
{
unsigned value;
struct list waiters;
};
void
void
bool
void
void
sema_init (struct semaphore *, unsigned val);
sema_down (struct semaphore *);
sema_try_down (struct semaphore *);
sema_up (struct semaphore *);
sema_self_test (void);
/* Lock. */
struct lock
{
struct thread *holder;
/* For debug */
struct semaphore semaphore;
};
void
void
bool
void
lock_init (struct lock *);
lock_acquire (struct lock *);
lock_try_acquire (struct lock *);
lock_release (struct lock *);
/* Condition variable. */
struct condition
{
struct list waiters;
};
cond_init (struct condition *);
cond_wait (struct condition *, struct lock *);
cond_signal (struct condition *, struct lock *);
cond_broadcast (struct condition *, struct lock *);
/*
− Locks must be used on ALL accesses (read and
write) to be effective
− Conditions are critical and REQUIRE a lock
− Conditions ALWAYS have your custom expression to
determine if the condition is true or false
− Signal on a condition will only awake one thread
that is ALREADY WAITING
− Up on a semaphore will EVENTUALLY (slutligen/till
slut) awake one thread, already waiting or not
yet waiting
− Down on a semaphore can be done twice by the same
thread
− A semaphore will allow any thread to Up it
− A lock will allow only the locker to release it
− A lock can never be Acqired if already held by
the thread
*/