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

NAME
     OSpinLockTry, OSpinLockLock, OSpinLockUnlock -- atomic spin lock syn-
     chronization primitives

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     ##include <>

     bool
     OSpinLockTry(OSpinLock *lock);

     void
     OSpinLockLock(OSpinLock *lock);

     void
     OSpinLockUnlock(OSpinLock *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.

     OSpinLock 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.

     OSpinLockLock() will spin if the lock is already held, but employs vari-
     ous strategies to back off, making it immune to most priority-inversion
     livelocks.  But because it can spin, it may be inefficient in some situa-
     tions.

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

     OSpinLockUnlock() unconditionally unlocks the lock by zeroing it.

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

SEE ALSO
     atomic(3), atomicqueue(3), barrier(3)

Darwin                           May 26, 2004                           Darwin