atomic.3   [plain text]

.Dd May 26, 2004
.Dt ATOMIC 3
.Os Darwin
.Sh NAME
.Nm OSAtomicAdd32 ,
.Nm OSAtomicIncrement32 ,
.Nm OSAtomicDecrement32 ,
.Nm OSAtomicOr32 ,
.Nm OSAtomicAnd32 ,
.Nm OSAtomicXor32 ,
.Nm OSAtomicAdd64 ,
.Nm OSAtomicIncrement64 ,
.Nm OSAtomicDecrement64 ,
.Nm OSAtomicCompareAndSwap32 ,
.Nm OSAtomicCompareAndSwap64 ,
.Nm OSAtomicTestAndSet ,
.Nm OSAtomicTestAndClear
.Nd atomic add, increment, decrement, or, and, xor, compare and swap, test and set, and test and clear
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In libkern/OSAtomic.h
.Ft int32_t
.Fn OSAtomicAdd32 "int32_t theAmount, int32_t *theValue"
.Ft int32_t
.Fn OSAtomicIncrement32 "int32_t *theValue"
.Ft int32_t
.Fn OSAtomicDecrement32 "int32_t *theValue"
.Ft int32_t
.Fn OSAtomicOr32 "uint32_t theMask, uint32_t *theValue"
.Ft int32_t
.Fn OSAtomicAnd32 "uint32_t theMask, uint32_t *theValue"
.Ft int32_t
.Fn OSAtomicXor32 "uint32_t theMask, uint32_t *theValue"
.Ft int64_t
.Fn OSAtomicAdd64 "int64_t theAmount, int64_t *theValue"
.Ft int64_t
.Fn OSAtomicIncrement64 "int64_t *theValue"
.Ft int64_t
.Fn OSAtomicDecrement64 "int64_t *theValue"
.Ft bool
.Fn OSAtomicCompareAndSwap32 "int32_t oldValue" "int32_t newValue" "int32_t *theValue"
.Ft bool
.Fn OSAtomicCompareAndSwap64 "int64_t oldValue" "int64_t newValue" "int64_t *theValue"
.Ft bool
.Fn OSAtomicTestAndSet "uint32_t n, void *theAddress"
.Ft bool
.Fn OSAtomicTestAndClear "uint32_t n, void *theAddress"
.Sh DESCRIPTION
These functions are thread and multiprocessor safe, but do not incorporate memory barriers
and thus cannot be used by themselves to synchronize shared memory other than the memory
being operated on (ie,
.Fa theValue
and
.Fa theAddress
).  The logical (and, or, xor) and bit test operations are layered on top of the
.Fn OSAtomicCompareAndSwap
primitives.  The memory address
.Fa theValue
must be naturally aligned, ie 32-bit aligned for 32-bit operations and 64-bit
aligned for 64-bit operations.  The 64-bit operations are only implemented for
64-bit processes.
.Pp
.Fn OSAtomicCompareAndSwap32
and
.Fn OSAtomicCompareAndSwap64
compare
.Fa oldValue
to
.Fa *theValue ,
and set
.Fa *theValue
to
.Fa newValue
if the comparison is equal.  The comparison and assignment
occur as one atomic operation.
.Pp
.Fn OSAtomicTestAndSet
and
.Fn OSAtomicTestAndClear
operate on bit (0x80 >> (
.Fa n
& 7)) of byte ((char*)
.Fa theAddress
+ (
.Fa n
>> 3)).  They set the named bit to either 1 or 0, respectively.
.Fa theAddress
need not be aligned.
.Sh RETURN VALUES
The arithmetic and logical operations return the new value, after the operation has been performed.
The compare-and-swap operations return true if the comparison was equal, ie if the swap occured.
The bit test and set/clear operations return the original value of the bit.
.Sh SEE ALSO
.Xr atomicqueue 3 ,
.Xr spinlock 3 ,
.Xr barrier 3