GIET-VM / Locks access functions

The locks.c and locks.h files define the functions used to take & release the kernel locks. These locks are implemented as spin-locks with a waiting queue (based on a ticket allocator scheme) to enforce fairness and avoid live-lock situations. The GIET_LOCK_MAX_TICKET define the wrapping value for the ticket allocator.

The lock access functions are prefixed by "_" to remind that they can only be executed by a processor in kernel mode.

The spin_lock_t structure is defined to have one single lock in a 64 bytes cache line, and should be aligned on a cache line boundary.

unsigned int _atomic_increment( unsigned int * shared , unsigned int increment )

This blocking function use a LL/SC to atomically increment a shared variable.

• shared : pointer on the shared variable
• increment : increment value

void _lock_init( spin_lock_t * lock )

This function initializes the spin lock ticket allocator.

void _lock_acquire( spin_lock_t * lock )

This blocking function uses the atomic_increment() function, and returns only when the lock as been granted.

void _lock_release( giet_lock_t * lock )

This function releases the spin-lock. It must always be called after a successful _lock_acquire().