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PTHREAD_ATTR_GETGUARDSIZE(PPOSIX Programmer's ManuPTHREAD_ATTR_GETGUARDSIZE(P)



PROLOG
       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
       pthread_attr_getguardsize, pthread_attr_setguardsize - get and set  the
       thread guardsize attribute

SYNOPSIS
       #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
       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 guard-
       size 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()	speci-
       fying attr shall store in the guardsize parameter the guard size speci-
       fied by the previous pthread_attr_setguardsize() function call.

       The default value of the guardsize attribute is {PAGESIZE} bytes.   The
       actual value of {PAGESIZE} is implementation-defined.

       If  the	stackaddr or stack 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.

RETURN VALUE
       If successful, the  pthread_attr_getguardsize()	and  pthread_attr_set-
       guardsize()  functions  shall  return  zero; otherwise, an error number
       shall be returned to indicate the error.

ERRORS
       The pthread_attr_getguardsize() and  pthread_attr_setguardsize()	 func-
       tions shall fail if:

       EINVAL The attribute attr is invalid.

       EINVAL The parameter guardsize is invalid.


       These functions shall not return an error code of [EINTR].

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       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.


FUTURE DIRECTIONS
       None.

SEE ALSO
       The  Base  Definitions  volume  of  IEEE Std 1003.1-2001,  <pthread.h>,
       <sys/mman.h>

COPYRIGHT
       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003	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 .



IEEE/The Open Group		     2003	  PTHREAD_ATTR_GETGUARDSIZE(P)
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