pthread_attr_getguardsize(3C)											     pthread_attr_getguardsize(3C)

NAME

       pthread_attr_getguardsize, pthread_attr_setguardsize - get or set thread guardsize attribute

SYNOPSIS

       cc -mt [ flag... ] file... -lpthread [ library... ]
       #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);

       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 guardsize
       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  0, a guard area will not be provided for threads created with attr. If guardsize is greater than
       0, a guard area of at least size guardsize bytes is provided for each thread created with attr.

       A conforming implementation is permitted to round up the value contained in guardsize to a multiple of  the  configurable  system  variable
       PAGESIZE.  If an implementation rounds up the value of guardsize to a multiple of  PAGESIZE, a call to pthread_attr_getguardsize() specify-
       ing attr will 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	PAGESIZE bytes. The actual value of  PAGESIZE is implementation-dependent and may  not	be
       the same on all implementations.

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

       If successful, the  pthread_attr_getguardsize() and pthread_attr_setguardsize() functions return  0. Otherwise, an error number is returned
       to indicate the error.

       The pthread_attr_getguardsize() and pthread_attr_setguardsize() functions will fail if:

       EINVAL	       The attribute attr is invalid.

       EINVAL	       The parameter guardsize is invalid.

       EINVAL	       The parameter guardsize contains an invalid value.

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

       sysconf(3C), pthread_attr_init(3C), attributes(5), standards(5)

								    23 mar 2005 				     pthread_attr_getguardsize(3C)