pthread_attr_setguardsize(3P)			 pthread_attr_setguardsize(3P)

NAME    [Toc]    [Back]

     pthread_attr_setguardsize,	pthread_attr_getguardsize - get	or set the
     thread guardsize attribute

C SYNOPSIS    [Toc]    [Back]

     #include <pthread.h>

     int pthread_attr_setguardsize(pthread_attr_t *attr, size_t	guardsize);

     int pthread_attr_getguardsize(const pthread_attr_t	*attr,
	  size_t *oguardsize);

DESCRIPTION    [Toc]    [Back]

     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 results
     (possibly in a SIGSEGV signal being delivered to the thread).

     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 will 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 pthread_attr_getguardsize() function gets the guardsize attribute in
     the attr object.  This attribute is returned in the oguardsize parameter.

     The pthread_attr_setguardsize() function sets the guardsize attribute in
     the attr object.  The new value of	this attribute is obtained from	the
     guardsize parameter.  If guardsize	is zero, a guard area will not be
     provided for threads created with attr.  If guardsize is greater than
     zero, a guard area	of at least size guardsize bytes is provided for each
     thread created with attr.

     IRIX rounds up the	value of guardsize to a	multiple of the	configurable
     system variable PAGESIZE (see <sys/mman.h>).  However,
     pthread_attr_getguardsize() will return the guard size specified by the
     previous call to pthread_attr_setguardsize().

     The default value of the guardsize	attribute is PAGESIZE bytes.  The
     actual value of PAGESIZE is system-dependent and may vary.

     If	the stackaddr attribute	has been set (that is, the caller is
     allocating	and managing its own thread stacks), the guardsize attribute
     is	ignored	and no protection will be provided by the implementation.  It



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pthread_attr_setguardsize(3P)			 pthread_attr_setguardsize(3P)



     is	the responsibility of the application to manage	stack overflow along
     with stack	allocation and management in this case.

DIAGNOSTICS    [Toc]    [Back]

     The functions pthread_attr_getguardsize() and pthread_attr_setguardsize()
     always return zero.

SEE ALSO    [Toc]    [Back]

     pthread_attr_init(3P), pthread_create(3P).


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