08-26-2010
"volatile" has nothing to do with atomic, "volatile" just tells the compiler to never assume that variable is whatever it set it to last. (otherwise, it might assume it never changes and hardcode it in the instructions.)
No variables (except the gcc atomic extensions) are guaranteed to be atomic, at all, ever. There's other problems than being atomic, too -- on a multicore system, one core might have a different copy of the memory still in cache, causing even "volatile" to fail. You need to inform other cores you're modifying values out from under them, which is what memory barriers are for. pthreads does memory barriers for you. I don't know if gcc atomic ops do.
Last edited by Corona688; 08-26-2010 at 05:33 PM..
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LEARN ABOUT NETBSD
atomic_dec_ulong
ATOMIC_DEC(3) BSD Library Functions Manual ATOMIC_DEC(3)
NAME
atomic_dec, atomic_dec_32, atomic_dec_uint, atomic_dec_ulong, atomic_dec_ptr, atomic_dec_64, atomic_dec_32_nv, atomic_dec_uint_nv,
atomic_dec_ulong_nv, atomic_dec_ptr_nv, atomic_dec_64_nv -- atomic decrement operations
SYNOPSIS
#include <sys/atomic.h>
void
atomic_dec_32(volatile uint32_t *ptr);
void
atomic_dec_uint(volatile unsigned int *ptr);
void
atomic_dec_ulong(volatile unsigned long *ptr);
void
atomic_dec_ptr(volatile void *ptr);
void
atomic_dec_64(volatile uint64_t *ptr);
uint32_t
atomic_dec_32_nv(volatile uint32_t *ptr);
unsigned int
atomic_dec_uint_nv(volatile unsigned int *ptr);
unsigned long
atomic_dec_ulong_nv(volatile unsigned long *ptr);
void *
atomic_dec_ptr_nv(volatile void *ptr);
uint64_t
atomic_dec_64_nv(volatile uint64_t *ptr);
DESCRIPTION
The atomic_dec family of functions decrement (by one) the variable referenced by ptr in an atomic fashion.
The *_nv() variants of these functions return the new value.
The 64-bit variants of these functions are available only on platforms that can support atomic 64-bit memory access. Applications can check
for the availability of 64-bit atomic memory operations by testing if the pre-processor macro __HAVE_ATOMIC64_OPS is defined.
SEE ALSO
atomic_ops(3)
HISTORY
The atomic_dec functions first appeared in NetBSD 5.0.
BSD
April 11, 2007 BSD