PTHREAD_ATTR_GETGUARDSIZE(PPOSIX Programmer's ManuPTHREAD_ATTR_GETGUARDSIZE(P)NAME
pthread_attr_getguardsize, pthread_attr_setguardsize - get and set the
thread guardsize attribute
SYNOPSIS
#include <pthread.h>
int pthread_attr_getguardsize(const pthread_attr_t *restrict attr,
size_t *restrict guardsize);
int pthread_attr_setguardsize(pthread_attr_t *attr,
size_t guardsize);
DESCRIPTION
The pthread_attr_getguardsize() function shall get the guardsize
attribute in the attr object. This attribute shall be returned in the
guardsize parameter.
The pthread_attr_setguardsize() function shall set the guardsize
attribute in the attr object. The new value of this attribute shall be
obtained from the guardsize parameter. If guardsize is zero, a guard
area shall not be provided for threads created with attr. If guardsize
is greater than zero, a guard area of at least size guardsize bytes
shall be provided for each thread created with attr.
The guardsize attribute controls the size of the guard area for the
created thread's stack. The guardsize attribute provides protection
against overflow of the stack pointer. If a thread's stack is created
with guard protection, the implementation allocates extra memory at the
overflow end of the stack as a buffer against stack overflow of the
stack pointer. If an application overflows into this buffer an error
shall result (possibly in a SIGSEGV signal being delivered to the
thread).
A conforming implementation may round up the value contained in guard‐
size to a multiple of the configurable system variable {PAGESIZE} (see
<sys/mman.h>). If an implementation rounds up the value of guardsize to
a multiple of {PAGESIZE}, a call to pthread_attr_getguardsize() speci‐
fying attr shall store in the guardsize parameter the guard size speci‐
fied by the previous pthread_attr_setguardsize() function call.
The default value of the guardsize attribute is {PAGESIZE} bytes. The
actual value of {PAGESIZE} is implementation-defined.
If the stackaddr or stack attribute has been set (that is, the caller
is allocating and managing its own thread stacks), the guardsize
attribute shall be ignored and no protection shall be provided by the
implementation. It is the responsibility of the application to manage
stack overflow along with stack allocation and management in this case.
RETURN VALUE
If successful, the pthread_attr_getguardsize() and pthread_attr_set‐
guardsize() functions shall return zero; otherwise, an error number
shall be returned to indicate the error.
ERRORS
The pthread_attr_getguardsize() and pthread_attr_setguardsize() func‐
tions shall fail if:
EINVAL The attribute attr is invalid.
EINVAL The parameter guardsize is invalid.
These functions shall not return an error code of [EINTR].
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
The guardsize attribute is provided to the application for two reasons:
1. Overflow protection can potentially result in wasted system
resources. An application that creates a large number of threads,
and which knows its threads never overflow their stack, can save
system resources by turning off guard areas.
2. When threads allocate large data structures on the stack, large
guard areas may be needed to detect stack overflow.
FUTURE DIRECTIONS
None.
SEE ALSO
The Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>,
<sys/mman.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 PTHREAD_ATTR_GETGUARDSIZE(P)
