GET_ROBUST_LIST(2) Linux System Calls GET_ROBUST_LIST(2)
NAME
get_robust_list, set_robust_list - get/set list of robust futexes
SYNOPSIS
#include <linux/futex.h>
#include <sys/types.h>
#include <syscall.h>
long get_robust_list(int pid, struct robust_list_head **head_ptr,
size_t *len_ptr);
long set_robust_list(struct robust_list_head *head, size_t len);
Note: There are no glibc wrappers for these system calls; see NOTES.
DESCRIPTION
These system calls deal with per-thread robust futex lists. These
lists are managed in user space: the kernel knows only about the loca-
tion of the head of the list. A thread can inform the kernel of the
location of its robust futex list using set_robust_list(). The address
of a thread's robust futex list can be obtained using
get_robust_list().
The purpose of the robust futex list is to ensure that if a thread
accidentally fails to unlock a futex before terminating or calling
execve(2), another thread that is waiting on that futex is notified
that the former owner of the futex has died. This notification con-
sists of two pieces: the FUTEX_OWNER_DIED bit is set in the futex word,
and the kernel performs a futex(2) FUTEX_WAKE operation on one of the
threads waiting on the futex.
The get_robust_list() system call returns the head of the robust futex
list of the thread whose thread ID is specified in pid. If pid is 0,
the head of the list for the calling thread is returned. The list head
is stored in the location pointed to by head_ptr. The size of the
object pointed to by **head_ptr is stored in len_ptr.
Permission to employ get_robust_list() is governed by a ptrace access
mode PTRACE_MODE_READ_REALCREDS check; see ptrace(2).
The set_robust_list() system call requests the kernel to record the
head of the list of robust futexes owned by the calling thread. The
head argument is the list head to record. The len argument should be
sizeof(*head).
RETURN VALUE
The set_robust_list() and get_robust_list() system calls return zero
when the operation is successful, an error code otherwise.
ERRORS
The set_robust_list() system call can fail with the following error:
EINVAL len does not equal sizeof(struct robust_list_head).
The get_robust_list() system call can fail with the following errors:
EPERM The calling process does not have permission to see the robust
futex list of the thread with the thread ID pid, and does not
have the CAP_SYS_PTRACE capability.
ESRCH No thread with the thread ID pid could be found.
EFAULT The head of the robust futex list can't be stored at the loca-
tion head.
VERSIONS
These system calls were added in Linux 2.6.17.
NOTES
These system calls are not needed by normal applications. No support
for them is provided in glibc. In the unlikely event that you want to
call them directly, use syscall(2).
A thread can have only one robust futex list; therefore applications
that wish to use this functionality should use the robust mutexes pro-
vided by glibc.
In the initial implementation, a thread waiting on a futex was notified
that the owner had died only if the owner terminated. Starting with
Linux 2.6.28, notification was extended to include the case where the
owner performs an execve(2).
The thread IDs mentioned in the main text are kernel thread IDs of the
kind returned by clone(2) and gettid(2).
SEE ALSO
futex(2), pthread_mutexattr_setrobust(3)
Documentation/robust-futexes.txt and Documentation/robust-futex-ABI.txt
in the Linux kernel source tree
COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 GET_ROBUST_LIST(2)
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