pthread_attr_getguardsize(3p) — Linux manual page



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 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.

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

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

       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.1‐2017, pthread.h(0p),

COPYRIGHT         top

       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 .

       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               2017            PTHREAD...UARDSIZE(3P)

Pages that refer to this page: pthread.h(0p)pthread_attr_setguardsize(3p)