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man:get_robust_list

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 4.16 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)

/data/webs/external/dokuwiki/data/pages/man/get_robust_list.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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