NAME¶
pthread_attr_setguardsize, pthread_attr_getguardsize - set/get guard size
attribute in thread attributes object
SYNOPSIS¶
#include <pthread.h>
int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);
int pthread_attr_getguardsize(const 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 nonzero 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.
ATTRIBUTES¶
Multithreading (see pthreads(7))¶
The
pthread_attr_setguardsize() and
pthread_attr_getguardsize()
functions are thread-safe.
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.
EXAMPLE¶
See
pthread_getattr_np(3).
SEE ALSO¶
mmap(2),
mprotect(2),
pthread_attr_init(3),
pthread_attr_setstack(3),
pthread_attr_setstacksize(3),
pthread_create(3),
pthreads(7)
COLOPHON¶
This page is part of release 3.74 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
http://www.kernel.org/doc/man-pages/.
