Chapter 6. The trylock Functions
There are functions that try to acquire a lock only once and immediately
return a value telling about success or failure to acquire the lock.
They can be used if you need no access to the data protected with the lock
when some other thread is holding the lock. You should acquire the lock
later if you then need access to the data protected with the lock.
spin_trylock() does not spin but returns non-zero if
it acquires the spinlock on the first try or 0 if not. This function can
be used in all contexts like spin_lock: you must have
disabled the contexts that might interrupt you and acquire the spin lock.
mutex_trylock() does not suspend your task
but returns non-zero if it could lock the mutex on the first try
or 0 if not. This function cannot be safely used in hardware or software
interrupt contexts despite not sleeping.