spinlock_deprecated.3   [plain text]

.Dd May 26, 2004
.Dt SPINLOCK_DEPRECATED 3
.Os Darwin
.Sh NAME
.Nm OSSpinLockTry ,
.Nm OSSpinLockLock ,
.Nm OSSpinLockUnlock
.Nd deprecated atomic spin lock synchronization primitives
.Sh SYNOPSIS
.In libkern/OSAtomic.h
.Ft bool
.Fn OSSpinLockTry "OSSpinLock *lock"
.Ft void
.Fn OSSpinLockLock "OSSpinLock *lock"
.Ft void
.Fn OSSpinLockUnlock "OSSpinLock *lock"
.Sh DESCRIPTION
.Bf -symbolic
These are deprecated interfaces for userspace spinlocks, provided for
compatibility with legacy code. These interfaces should no longer be used,
particularily in situations where threads of differing priorities may contend
on the same spinlock.
.Pp
The interfaces in
.In os/lock.h
should be used instead in cases where a very low-level lock primitive is
required. In general however, using higher level synchronization primitives
such as those provided by the pthread or dispatch subsystems are preferred.
.Ef
.Pp
The OSSpinLock operations use memory barriers to synchronize access to shared
memory protected by the lock.  Preemption is possible while the lock is held.
.Pp
.Ft 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.
.Pp
.Fn OSSpinLockLock
will spin if the lock is already held, but employs various strategies to back
off. Because it can spin, it will generally be less cpu and power efficient than
other synchronization primitives.
.Pp
.Fn OSSpinLockTry
immediately returns false if the lock was held, true if it took the lock.
It does not spin.
.Pp
.Fn OSSpinLockUnlock
unconditionally unlocks the lock by zeroing it.
.Sh RETURN VALUES
.Fn OSSpinLockTry
returns true if it took the lock, false if the lock was already held.
.Sh SEE ALSO
.Xr atomic 3 ,
.Xr atomic_deprecated 3