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)