_spin_lock(SYNCH)

_spin_lock -- lock a spin lock

Synopsis

   cc [options] -Kthread file
   
   #include <synch.h>
   

   void _spin_lock(spin_t *lock);

Description

_spin_lock locks the spin lock pointed to by lock. If lock is locked, the calling thread will busy-wait, or ``spin'', until lock is available. When _spin_lock returns, the caller has acquired lock.

lock must previously have been initialized (see _spin_init(SYNCH)).

Parameters

lock: pointer to spin lock to be locked

Return values

_spin_lock does not return a value.

Errors

None

Usage

Because spin locks waste system resources, most applications should use mutexes instead of spin locks for mutual exclusion. In general, _spin_lock is used when the resources are held exclusively for such short durations that the expected spin is less costly than blocking and resuming the thread.

Spin locks should only be used when there is a guarantee that the thread will not be preempted or blocked while holding a spin lock.

The locks acquired with _spin_lock should be released with _spin_unlock.

Warnings

Spin locks must not be used on a single processor system. In the best case, a spin lock on a single processor system will waste resources, slowing down the owner of the lock; in the worst case, it will deadlock the processor.

Operations on spin locks are not recursive--a thread can deadlock if it attempts to relock a spin lock that it already has locked.

References

Intro(SYNCH), _spin(SYNCH), _spin_destroy(SYNCH), _spin_init(SYNCH), _spin_trylock(SYNCH), _spin_unlock(SYNCH)