PROLOG         top

       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.

NAME         top

       pthread_attr_getguardsize, pthread_attr_setguardsize — get and set
       the thread guardsize attribute

SYNOPSIS         top

       #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         top

       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-

       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

       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.

RETURN VALUE         top

       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.

ERRORS         top

       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.

EXAMPLES         top

   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 */



RATIONALE         top

       The guardsize attribute is provided to the application for two

        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.



SEE ALSO         top

       The Base Definitions volume of POSIX.1‐2008, pthread.h(0p),

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group                 2013       PTHREAD_ATTR_GETGUARDSIZE(3P)