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futex.2: Make the example use C11 atomics rather than GCC builtins 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Benjamin Peterson 2018-11-13 22:53:41 -08:00 committed by Michael Kerrisk
parent 1605ddac8f
commit 915c4ba36f
1 changed files with 10 additions and 12 deletions
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22
man2/futex.2
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@ -1756,6 +1756,7 @@ Child (18535) 4
#define _GNU_SOURCE
#include <stdio.h>
#include <errno.h>
#include <stdatomic.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
@ -1785,22 +1786,19 @@ fwait(int *futexp)
{
int s;
/* __sync_bool_compare_and_swap(ptr, oldval, newval) is a gcc
built\-in function. It atomically performs the equivalent of:
/* atomic_compare_exchange_strong(ptr, oldval, newval)
atomically performs the equivalent of:
if (*ptr == oldval)
if (*ptr == *oldval)
*ptr = newval;
It returns true if the test yielded true and *ptr was updated.
The alternative here would be to employ the equivalent atomic
machine\-language instructions. For further information, see
the GCC Manual. */
It returns true if the test yielded true and *ptr was updated. */
while (1) {
/* Is the futex available? */
if (__sync_bool_compare_and_swap(futexp, 1, 0))
const int zero = 0;
if (atomic_compare_exchange_strong(futexp, &zero, 1))
break; /* Yes */
/* Futex is not available; wait */
@ -1820,10 +1818,10 @@ fpost(int *futexp)
{
int s;
/* __sync_bool_compare_and_swap() was described in comments above */
if (__sync_bool_compare_and_swap(futexp, 0, 1)) {
/* atomic_compare_exchange_strong() was described in comments above */
const int one = 1;
if (atomic_compare_exchange_strong(futexp, &one, 0)) {
s = futex(futexp, FUTEX_WAKE, 1, NULL, NULL, 0);
if (s == \-1)
errExit("futex\-FUTEX_WAKE");