ATOMIC(3)						   BSD Library Functions Manual 						 ATOMIC(3)

NAME

     OSAtomicEnqueue, OSAtomicDequeue -- atomic lockless queues

SYNOPSIS

     #include <libkern/OSAtomic.h>

     void
     OSAtomicEnqueue(OSQueueHead *list, void *new, size_t offset);

     void*
     OSAtomicDequeue(OSQueueHead *list, size_t offset);

DESCRIPTION

     The routines OSAtomicEnqueue() and OSAtomicDequeue() operate on singly linked LIFO queues.  Ie, a dequeue operation will return the most
     recently enqueued element, or NULL if the list is empty.  The operations are lockless, and barriers are used as necessary to permit thread-
     safe access to the queue element.	offset is the offset in bytes to the link field in the queue element.

     Important: the memory backing the link field of a queue element must not be unmapped after OSAtomicDequeue() returns until all concurrent
     calls to OSAtomicDequeue() for the same list on other threads have also returned, as they may still be accessing that memory location.

EXAMPLES

		   typedef struct elem {
			   long    data1;
			   struct elem *link;
			   int	   data2;
		   } elem_t;

		   elem_t fred, mary, *p;

		   OSQueueHead q = OS_ATOMIC_QUEUE_INIT;

		   OSAtomicEnqueue( &q, &fred, offsetof(elem_t,link) );
		   OSAtomicEnqueue( &q, &mary, offsetof(elem_t,link) );

		   p = OSAtomicDequeue( &q, offsetof(elem_t,link) );

     In this example, the call of OSAtomicDequeue() will return a ptr to mary.

RETURN VALUES

     The dequeue operation returns the most recently enqueued element, or NULL if the list in empty.

SEE ALSO

     stdatomic(3), atomic_deprecated(3), spinlock_deprecated(3)

HISTORY

     These functions first appeared in Mac OS 10.5 (Leopard).

Darwin								   May 26, 2004 							    Darwin