PTHREAD_ATTR_GETGUARDSIZE(3C) Standard C Library Functions

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);

DESCRIPTION

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() specifying 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.

RETURN VALUES

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

ERRORS

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.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


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

SEE ALSO

pthread_attr_init(3C), sysconf(3C), attributes(7), standards(7)

March 23, 2005 PTHREAD_ATTR_GETGUARDSIZE(3C)