get_robust_list, set_robust_list — get/set list of robust futexes


#include <linux/futex.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] Note
There are no glibc wrappers for these system calls; see NOTES.


The robust futex implementation needs to maintain per-thread lists of robust futexes which are unlocked when the thread exits. These lists are managed in user space; the kernel is notified about only the location of the head of the list.

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.

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).


The set_robust_list() and get_robust_list() system calls return zero when the operation is successful, an error code otherwise.


The set_robust_list() system call can fail with the following error:


len does not match the size of structure struct robust_list_head expected by kernel.

The get_robust_list() system call can fail with the following errors:


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.


No thread with the thread ID pid could be found.


The head of the robust futex list can't be stored at the location head.


These system calls were added in Linux 2.6.17. No library support is provided; use syscall(2).


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 provided by glibc.



Documentation/robust-futexes.txt and Documentation/robust-futex-ABI.txt in the Linux kernel source tree


This page is part of release 3.52 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at−pages/.

  Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
Written by Ivana Varekova <>

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FIXME Something could be added to this page (or exit(2))
      about exit_robust_list processing