[lkml]   [2014]   [Aug]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: Does anyone know when FUTEX_WAIT can fail with EAGAIN?
Steven Stewart-Gallus <> wrote:
> I'm trying to debug a hangup where my program loops with FUTEX_WAIT (actually
> FUTEX_WAIT_PRIVATE but same thing) endlessly erring out with EAGAIN. I would
> like to know if anyone on the mailing list knows when FUTEX_WAIT can fail with

FUTEX_WAIT fails with EAGAIN if the value of *uaddr no longer matches
the expected val.
#include <linux/futex.h>
#include <sys/syscall.h>
#include <unistd.h>
#include <errno.h>
int main(void) {
int op = FUTEX_WAIT;
int exp = 1;
int *addr = &exp;
int val = 1; /* XXX change this to anything else to get EAGAIN */
int rc = syscall(SYS_futex, addr, op, val, 0, 0, 0);

if (rc < 0 && errno == EAGAIN)
write(1, "EAGAIN\n", 7);

return 0;
I just encountered this myself yesterday while implementing futex-based
locks/condvars for Ruby:

 \ /
  Last update: 2014-08-17 00:21    [W:0.041 / U:0.104 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site