pthread_attr_getguardsize(3p) — Linux manual page

PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

PTHREAD_ATTR_GETGUARDSIZE(3P) Programmer's ManualD_ATTR_GETGUARDSIZE(3P)

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-
       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.

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 */
               ...
               }
           }

APPLICATION USAGE         top

       None.

RATIONALE         top

       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.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       The Base Definitions volume of POSIX.1‐2017, pthread.h(0p),
       sys_mman.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 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_ATTR_GETGUARDSIZE(3P)

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