PTHREAD_ATTR_GETGUARDSIZE(3)				   BSD Library Functions Manual 			      PTHREAD_ATTR_GETGUARDSIZE(3)

NAME

     pthread_attr_getguardsize -- get and set thread guard size

LIBRARY

     POSIX Threads Library (libpthread, -lpthread)

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() and pthread_attr_setguardsize() functions get and set guardsize in the attr object.  If guardsize is larger
     than 0, the system reserves an additional region of guarded memory of at least guardsize bytes at the end of the thread's stack for each new
     thread created by using attr.

     The guarded area is understood to be pages of memory that are protected from read and write access.  While the guarded area should be rounded
     by the system page size, the actual default size is implementation-defined.  In NetBSD the default guardsize is _SC_PAGESIZE, the system page
     size.

     The rationale behind guardsize is two-fold:

       1.   On the one hand, it provides protection against overflow of the stack pointer.  If there is a guard area and a thread overflows its
	    stack pointer into this extra memory area, it should receive a SIGSEGV signal or experience other comparable fatal error condition.
	    Note that if a thread allocates large data structures on stack, it may be necessary to raise the default guardsize in order to detect
	    stack overflows.

       2.   On the other hand, the overflow protection may waste system resources if an application that creates a large number of threads knows
	    that it will never overflow the stack.  In this case it is possible to set guardsize to 0.

     If pthread_attr_setstack(3) or pthread_attr_setstackaddr(3) is used to set the stack address attribute in attr, the guard size attribute is
     ignored and no guard area will be allocated; it is the responsibility of the application to handle the overflow conditions.

RETURN VALUES

     If successful, both functions return 0.  Otherwise, an error number is returned to indicate the error.

ERRORS

     No errors are defined for pthread_attr_getguardsize().

     The pthread_attr_setguardsize() may fail if:

     [ENOMEM]		There was insufficient memory.

SEE ALSO

     pthread_attr(3), pthread_attr_setstack(3), sysconf(3)

STANDARDS

     Both functions conform to IEEE Std 1003.1-2008 (``POSIX.1'').

BSD
								   July 7, 2010 							       BSD