atomic_deprecated.3   [plain text]

.Dd May 26, 2004
.Dt ATOMIC_DEPRECATED 3
.Os Darwin
.Sh NAME
.Nm OSAtomicAdd32 ,
.Nm OSAtomicAdd32Barrier ,
.Nm OSAtomicIncrement32 ,
.Nm OSAtomicIncrement32Barrier ,
.Nm OSAtomicDecrement32 ,
.Nm OSAtomicDecrement32Barrier ,
.Nm OSAtomicOr32 ,
.Nm OSAtomicOr32Barrier ,
.Nm OSAtomicOr32Orig ,
.Nm OSAtomicOr32OrigBarrier ,
.Nm OSAtomicAnd32 ,
.Nm OSAtomicAnd32Barrier ,
.Nm OSAtomicAnd32Orig ,
.Nm OSAtomicAnd32OrigBarrier ,
.Nm OSAtomicXor32 ,
.Nm OSAtomicXor32Barrier ,
.Nm OSAtomicXor32Orig ,
.Nm OSAtomicXor32OrigBarrier ,
.Nm OSAtomicAdd64 ,
.Nm OSAtomicAdd64Barrier ,
.Nm OSAtomicIncrement64 ,
.Nm OSAtomicIncrement64Barrier ,
.Nm OSAtomicDecrement64 ,
.Nm OSAtomicDecrement64Barrier ,
.Nm OSAtomicCompareAndSwapInt ,
.Nm OSAtomicCompareAndSwapIntBarrier ,
.Nm OSAtomicCompareAndSwapLong ,
.Nm OSAtomicCompareAndSwapLongBarrier ,
.Nm OSAtomicCompareAndSwapPtr ,
.Nm OSAtomicCompareAndSwapPtrBarrier ,
.Nm OSAtomicCompareAndSwap32 ,
.Nm OSAtomicCompareAndSwap32Barrier ,
.Nm OSAtomicCompareAndSwap64 ,
.Nm OSAtomicCompareAndSwap64Barrier ,
.Nm OSAtomicTestAndSet ,
.Nm OSAtomicTestAndSetBarrier ,
.Nm OSAtomicTestAndClear ,
.Nm OSAtomicTestAndClearBarrier ,
.Nm OSMemoryBarrier
.Nd deprecated atomic add, increment, decrement, or, and, xor, compare and swap, test and set, test and clear, and memory barrier
.Sh SYNOPSIS
.In libkern/OSAtomic.h
.Ft int32_t
.Fn OSAtomicAdd32 "int32_t theAmount" "volatile int32_t *theValue"
.Ft int32_t
.Fn OSAtomicAdd32Barrier "int32_t theAmount" "volatile int32_t *theValue"
.Ft int32_t
.Fn OSAtomicIncrement32 "volatile int32_t *theValue"
.Ft int32_t
.Fn OSAtomicIncrement32Barrier "volatile int32_t *theValue"
.Ft int32_t
.Fn OSAtomicDecrement32 "volatile int32_t *theValue"
.Ft int32_t
.Fn OSAtomicDecrement32Barrier "volatile int32_t *theValue"
.Ft int32_t
.Fn OSAtomicOr32 "uint32_t theMask" "volatile uint32_t *theValue"
.Ft int32_t
.Fn OSAtomicOr32Barrier "uint32_t theMask" "volatile uint32_t *theValue"
.Ft int32_t
.Fn OSAtomicAnd32 "uint32_t theMask" "volatile uint32_t *theValue"
.Ft int32_t
.Fn OSAtomicAnd32Barrier "uint32_t theMask" "volatile uint32_t *theValue"
.Ft int32_t
.Fn OSAtomicXor32 "uint32_t theMask" "volatile uint32_t *theValue"
.Ft int32_t
.Fn OSAtomicXor32Barrier "uint32_t theMask" "volatile uint32_t *theValue"
.Ft int32_t
.Fn OSAtomicOr32Orig "uint32_t theMask" "volatile uint32_t *theValue"
.Ft int32_t
.Fn OSAtomicOr32OrigBarrier "uint32_t theMask" "volatile uint32_t *theValue"
.Ft int32_t
.Fn OSAtomicAnd32Orig "uint32_t theMask" "volatile uint32_t *theValue"
.Ft int32_t
.Fn OSAtomicAnd32OrigBarrier "uint32_t theMask" "volatile uint32_t *theValue"
.Ft int32_t
.Fn OSAtomicXor32Orig "uint32_t theMask" "volatile uint32_t *theValue"
.Ft int32_t
.Fn OSAtomicXor32OrigBarrier "uint32_t theMask" "volatile uint32_t *theValue"
.Ft int64_t
.Fn OSAtomicAdd64 "int64_t theAmount" "volatile OSAtomic_int64_aligned64_t *theValue"
.Ft int64_t
.Fn OSAtomicAdd64Barrier "int64_t theAmount" "volatile OSAtomic_int64_aligned64_t *theValue"
.Ft int64_t
.Fn OSAtomicIncrement64 "volatile OSAtomic_int64_aligned64_t *theValue"
.Ft int64_t
.Fn OSAtomicIncrement64Barrier "volatile OSAtomic_int64_aligned64_t *theValue"
.Ft int64_t
.Fn OSAtomicDecrement64 "volatile OSAtomic_int64_aligned64_t *theValue"
.Ft int64_t
.Fn OSAtomicDecrement64Barrier "volatile OSAtomic_int64_aligned64_t *theValue"
.Ft bool
.Fn OSAtomicCompareAndSwapInt "int oldValue" "int newValue" "volatile int *theValue"
.Ft bool
.Fn OSAtomicCompareAndSwapIntBarrier "int oldValue" "int newValue" "volatile int *theValue"
.Ft bool
.Fn OSAtomicCompareAndSwapLong "long oldValue" "long newValue" "volatile long *theValue"
.Ft bool
.Fn OSAtomicCompareAndSwapLongBarrier "long oldValue" "long newValue" "volatile long *theValue"
.Ft bool
.Fn OSAtomicCompareAndSwapPtr "void* oldValue" "void* newValue" "void* volatile *theValue"
.Ft bool
.Fn OSAtomicCompareAndSwapPtrBarrier "void* oldValue" "void* newValue" "void* volatile *theValue"
.Ft bool
.Fn OSAtomicCompareAndSwap32 "int32_t oldValue" "int32_t newValue" "volatile int32_t *theValue"
.Ft bool
.Fn OSAtomicCompareAndSwap32Barrier "int32_t oldValue" "int32_t newValue" "volatile int32_t *theValue"
.Ft bool
.Fn OSAtomicCompareAndSwap64 "int64_t oldValue" "int64_t newValue" "volatile OSAtomic_int64_aligned64_t *theValue"
.Ft bool
.Fn OSAtomicCompareAndSwap64Barrier "int64_t oldValue" "int64_t newValue" "volatile OSAtomic_int64_aligned64_t *theValue"
.Ft bool
.Fn OSAtomicTestAndSet "uint32_t n" "volatile void *theAddress"
.Ft bool
.Fn OSAtomicTestAndSetBarrier "uint32_t n" "volatile void *theAddress"
.Ft bool
.Fn OSAtomicTestAndClear "uint32_t n" "volatile void *theAddress"
.Ft bool
.Fn OSAtomicTestAndClearBarrier "uint32_t n" "volatile void *theAddress"
.Ft bool
.Fn OSAtomicEnqueue "OSQueueHead *list" "void *new" "size_t offset"
.Ft void*
.Fn OSAtomicDequeue "OSQueueHead *list" "size_t offset"
.Ft void
.Fn OSMemoryBarrier "void"
.Sh DESCRIPTION
.Bf -symbolic
These are deprecated interfaces for atomic and synchronization
operations, provided for compatibility with legacy code. New code should use
the C11
.In stdatomic.h
interfaces.
.Ef
.Pp
These functions are thread and multiprocessor safe.  For each function, there
is a version which incorporates a memory barrier and another version which does
not.
Barriers strictly order memory access on a weakly-ordered architecture such as
ARM. All loads and stores executed in sequential program
order before the barrier will complete before any load or store executed after
the barrier.
On some platforms, such as ARM, the barrier operation can be quite expensive.
.Pp
Most code will want to use the barrier functions to ensure that memory shared
between threads is properly synchronized.  For example, if you want to
initialize a shared data structure and then atomically increment a variable to
indicate that the initialization is complete, then you must use
.Fn OSAtomicIncrement32Barrier
to ensure that the stores to your data structure complete before the atomic add.
Likewise, the consumer of that data structure must use
.Fn OSAtomicDecrement32Barrier ,
in order to ensure that their loads of the structure are not executed before
the atomic decrement.  On the other hand, if you are simply incrementing a
global counter, then it is safe and potentially much faster to use
.Fn OSAtomicIncrement32 .
If you are unsure which version to use, prefer the barrier variants as they are
safer.
.Pp
The logical (and, or, xor) and bit test operations are layered on top of the
.Fn OSAtomicCompareAndSwap
primitives.  There are four versions of each logical operation, depending on
whether or not there is a barrier, and whether the return value is the result
of the operation (eg,
.Fn OSAtomicOr32
) or the original value before the operation (eg,
.Fn OSAtomicOr32Orig
).
.Pp
The memory address
.Fa theValue
must be "naturally aligned", i.e. 32-bit aligned for 32-bit operations and
64-bit aligned for 64-bit operations. Note that this is not the default alignment
of the
.Vt int64_t
in the iOS ARMv7 ABI, the
.Vt OSAtomic_int64_aligned64_t
type can be used to declare variables with the required alignment.
.Pp
The
.Fn OSAtomicCompareAndSwap
operations 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.
.Pp
The
.Fn OSMemoryBarrier
function strictly orders memory accesses in a weakly ordered memory model such
as with ARM, by creating a barrier.
All loads and stores executed in sequential program order before the barrier
will complete with respect to the memory coherence mechanism, before any load
or store executed after the barrier. Used with an atomic operation, the barrier
can be used to create custom synchronization protocols as an alternative to the
spinlock or queue/dequeue operations. Note that this barrier does not order
uncached loads and stores. On a uniprocessor, the barrier operation is
typically optimized into a no-op.
.Sh RETURN VALUES
The arithmetic operations return the new value, after the operation has been
performed. The boolean operations come in two styles, one of which returns the
new value, and one of which (the "Orig" versions) returns the old.
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 atomic 3 ,
.Xr spinlock_deprecated 3
.Sh HISTORY
Most of these functions first appeared in Mac OS 10.4 (Tiger).  The "Orig"
forms of the boolean operations, the "int", "long" and "ptr" forms of
compare-and-swap first appeared in Mac OS 10.5 (Leopard).