NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | NOTES | SEE ALSO | COLOPHON

GET_ROBUST_LIST(2)           Linux System Calls           GET_ROBUST_LIST(2)

NAME         top

       get_robust_list, set_robust_list - get/set list of robust futexes

SYNOPSIS         top

       #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         top

       These system calls deal with per-thread robust futex lists.  These
       lists are managed in user space: the kernel knows only about the
       location 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
       consists 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         top

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

ERRORS         top

       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
              location head.

VERSIONS         top

       These system calls were added in Linux 2.6.17.

NOTES         top

       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.

       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         top

       futex(2), pthread_mutexattr_setrobust(3)

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

COLOPHON         top

       This page is part of release 4.13 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)

Pages that refer to this page: execve(2)futex(2)gettid(2)ptrace(2)syscalls(2)exit(3)pthread_mutexattr_setrobust(3)capabilities(7)futex(7)