#include <pthread.h>int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);int pthread_attr_getguardsize(pthread_attr_t *attr, size_t *guardsize);
Compile and link with -pthread.
DESCRIPTION
The
pthread_attr_setguardsize()
function sets the guard size attribute of the
thread attributes object referred to by
attr
to the value specified in
guardsize.
If
guardsize
is greater than 0,
then for each new thread created using
attr
the system allocates an additional region of at least
guardsize
bytes at the end of the thread's stack to act as the guard area
for the stack (but see BUGS).
If
guardsize
is 0, then new threads created with
attr
will not have a guard area.
The default guard size is the same as the system page size.
If the stack address attribute has been set in
attr
(using
pthread_attr_setstack(3)
or
pthread_attr_setstackaddr(3)),
meaning that the caller is allocating the thread's stack,
then the guard size attribute is ignored
(i.e., no guard area is created by the system):
it is the application's responsibility to handle stack overflow
(perhaps by using
mprotect(2)
to manually define a guard area at the end of the stack
that it has allocated).
The
pthread_attr_getguardsize()
function returns the guard size attribute of the
thread attributes object referred to by
attr
in the buffer pointed to by
guardsize.
RETURN VALUE
On success, these functions return 0;
on error, they return a non-zero error number.
ERRORS
POSIX.1-2001 documents an
EINVAL
error if
attr
or
guardsize
is invalid.
On Linux these functions always succeed
(but portable and future-proof applications should nevertheless
handle a possible error return).
VERSIONS
These functions are provided by glibc since version 2.1.
CONFORMING TO
POSIX.1-2001.
NOTES
A guard area consists of virtual memory pages that are protected
to prevent read and write access.
If a thread overflows its stack into the guard area,
then, on most hard architectures, it receives a
SIGSEGV
signal, thus notifying it of the overflow.
Guard areas start on page boundaries,
and the guard size is internally rounded up to
the system page size when creating a thread.
(Nevertheless,
pthread_attr_getguardsize()
returns the guard size that was set by
pthread_attr_setguardsize().)
Setting a guard size of 0 may be useful to save memory
in an application that creates many threads
and knows that stack overflow can never occur.
Choosing a guard size larger than the default size
may be necessary for detecting stack overflows
if a thread allocates large data structures on the stack.
BUGS
As at glibc 2.8, the NPTL threading implementation includes
the guard area within the stack size allocation,
rather than allocating extra space at the end of the stack,
as POSIX.1 requires.
(This can result in an
EINVAL
error from
pthread_create(3)
if the guard size value is too large,
leaving no space for the actual stack.)
The obsolete LinuxThreads implementation did the right thing,
allocating extra space at the end of the stack for the guard area.
This page is part of release 3.14 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
