osx man page for spinlock

SPINLOCK(3)						   BSD Library Functions Manual 					       SPINLOCK(3)

NAME
     OSSpinLockTry, OSSpinLockLock, OSSpinLockUnlock -- atomic spin lock synchronization primitives

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <libkern/OSAtomic.h>

     bool
     OSSpinLockTry(OSSpinLock *lock);

     void
     OSSpinLockLock(OSSpinLock *lock);

     void
     OSSpinLockUnlock(OSSpinLock *lock);

DESCRIPTION
     Spin locks are a simple, fast, thread-safe synchronization primitive that is suitable in situations where contention is expected to be low.
     The spinlock operations use memory barriers to synchronize access to shared memory protected by the lock.	Preemption is possible while the
     lock is held.

     OSSpinLock is an integer type.  The convention is that unlocked is zero, and locked is nonzero.  Locks must be naturally aligned and cannot
     be in cache-inhibited memory.

     OSSpinLockLock() will spin if the lock is already held, but employs various strategies to back off, making it immune to most priority-inver-
     sion livelocks.  But because it can spin, it may be inefficient in some situations.

     OSSpinLockTry() immediately returns false if the lock was held, true if it took the lock.	It does not spin.

     OSSpinLockUnlock() unconditionally unlocks the lock by zeroing it.

RETURN VALUES
     OSSpinLockTry() returns true if it took the lock, false if the lock was already held.

SEE ALSO
     atomic(3), barrier(3)

Darwin								   May 26, 2004 							    Darwin