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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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PTHREAD...UARDSIZE(3P) POSIX Programmer's Manual PTHREAD...UARDSIZE(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.1‐2017, pthread.h(0p),
sys_mman.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
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 2017 PTHREAD...UARDSIZE(3P)
Pages that refer to this page: pthread.h(0p), pthread_attr_setguardsize(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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