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.TH GET_ROBUST_LIST 2 "8 August 2006" Linux "Linux System Calls"
.SH NAME
get_robust_list, set_robust_list \- get/set the list of robust futexes
.SH SYNOPSIS
.nf
.B #include <linux/futex.h>
.B #include <syscall.h>
.sp
.BI "long get_robust_list(int " pid ", struct robust_list_head **" head_ptr ,
.BI "			  size_t *" len_ptr );
.BI "long set_robust_list(struct robust_list_head *" head ", size_t " len );
.fi
.SH DESCRIPTION
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 only notified about
the location of the head of the list.

.B get_robust_list
returns the head of the robust futex list of the thread with TID defined
by the
.I pid 
argument. If
.I pid
is 0, the returned head belongs to the current thread.
.I head_ptr
is the pointer to the head of the list of robust futexes. 
The
.B get_robust_list 
function stores the address of the head of the list here.
.I len_ptr 
is the pointer to the length variable. 
.B get_robust_list 
stores \fBsizeof(**\fIhead_ptr\fB)\fR here.

.B set_robust_list
sets the head of the list of robust futexes owned by the current thread to 
\fIhead\fR.
.I len
is the size of \fB*\fIhead\fR. 

.SH "RETURN VALUE"
The
.B set_robust_list
and 
.B get_robust_list
functions return zero when the operation is successful,
an error code otherwise.

.SH ERRORS
The
.B set_robust_list
function fails with
.B EINVAL 
if the 
.I len
value does not match the size of structure
.B struct robust_list_head 
expected by kernel.

The
.B get_robust_list
function fails with
.B EPERM 
if the current process does not have permission to see the robust futex list of
the thread with the TID
\fIpid\fR, 
.B ESRCH 
if a thread with the TID
.I pid
does not exist, or
.B EFAULT
if the head of the robust futex list can't be stored in the space specified by
the
.I head 
argument.

.SH APPLICATION USAGE
A thread can have only one robust futex list; therefore applications that wish
to use this functionality should use robust mutexes provided by glibc.

The system call is only available for debugging purposes and 
is not needed for normal operations. 

Both system calls are not available to application programs as functions;
they can be called using the
.BR syscall (3)
function.

.SH "SEE ALSO"
.BR futex (2),
.BR pthread_mutexattr_setrobust_np (3)