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PTHREAD_ATTR_GETGUARDSIZE(3P)IX Programmer's ManualEAD_ATTR_GETGUARDSIZE(3P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
pthread_attr_getguardsize, pthread_attr_setguardsize — get and set
the thread guardsize attribute
#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);
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
guardsize 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() specifying attr shall store in the
guardsize parameter the guard size specified by the previous
pthread_attr_setguardsize() function call.
The default value of the guardsize attribute is implementation-
defined.
If the stackaddr 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.
The behavior is undefined if the value specified by the attr argument
to pthread_attr_getguardsize() or pthread_attr_setguardsize() does
not refer to an initialized thread attributes object.
If successful, the pthread_attr_getguardsize() and
pthread_attr_setguardsize() functions shall return zero; otherwise,
an error number shall be returned to indicate the error.
These functions shall fail if:
EINVAL The parameter guardsize is invalid.
These functions shall not return an error code of [EINTR].
The following sections are informative.
Retrieving the guardsize Attribute
This example shows how to obtain the guardsize attribute of a thread
attribute object.
#include <pthread.h>
pthread_attr_t thread_attr;
size_t guardsize;
int rc;
/* code initializing thread_attr */
...
rc = pthread_attr_getguardsize (&thread_attr, &guardsize);
if (rc != 0) {
/* handle error */
...
}
else {
if (guardsize > 0) {
/* a guard area of at least guardsize bytes is provided */
...
}
else {
/* no guard area provided */
...
}
}
None.
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.
The default size of the guard area is left implementation-defined
since on systems supporting very large page sizes, the overhead might
be substantial if at least one guard page is required by default.
If an implementation detects that the value specified by the attr
argument to pthread_attr_getguardsize() or
pthread_attr_setguardsize() does not refer to an initialized thread
attributes object, it is recommended that the function should fail
and report an [EINVAL] error.
None.
The Base Definitions volume of POSIX.1‐2008, pthread.h(0p),
sys_mman.h(0p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 PTHREAD_ATTR_GETGUARDSIZE(3P)
Pages that refer to this page: pthread.h(0p), pthread_attr_setguardsize(3p)