atomic3
Atomic lockless queues
Usage
#include <libkern/OSAtomic.h>
void
OSAtomicEnqueue(OSQueueHead *list, void *new, size_t offset);
void*
OSAtomicDequeue(OSQueueHead *list, size_t offset);
Overview
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.
Releases
116 releases since Mac OS X 10.4; the text changed 4 times.