= The spin_lock library =

The [source:soft/giet_vm/giet_libs/spin_lock.c spin_lock.c] and [source:soft/giet_vm/giet_libs/spin_lock.h spin_lock.h] 
files define a user-level spin-lock service to obtain exclusive access to a shared resource in a parallel multi-tasks application.
Each lock (giet_lock_t object) occupies a complete 64 bytes cache line to avoid false sharing.
If the hardware architecture supports hardware cache coherence, it is recommanded to store the lock in a cachable segment architecture

 == Lock declaration ==

There is to ways to define a user-level lock, depending on the placement constraints:

 * If the lock is defined as a global variable in the application code, there is no precise control on the lock placement: the lock will be stored in the application global data ''vseg".

 * If the lock is defined as a specific ''vobj'' in the application mapping, it will be stored in the ''vseg'' specified in the mapping. The lock should not be declared as a global variable in the application code, and the lock virtual address can be obtained using the ''giet_vobj_get_vbase() system call.

 == Access functions ==

 * '''void lock_acquire( giet_lock_t * lock )'''
This blocking function uses an atomic LL/SC mechanism to take the lock, and return only when the lock has been successfully taken.

 * '''void lock_release( giet_lock_t * lock )'''
This function uses a simple SW to release the lock.