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);
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 parame‐
ter.
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 con‐
tained 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 allo‐
cating 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_set‐
guardsize() functions return 0. Otherwise, an error number is returned
to indicate the error.
ERRORS
The pthread_attr_getguardsize() and pthread_attr_setguardsize() func‐
tions 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(5) for descriptions of the following attributes:
┌────────────────────┬─────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼─────────────────┤
│Interface Stability │ Standard │
├────────────────────┼─────────────────┤
│MT-Level │ MT-Safe │
└────────────────────┴─────────────────┘
SEE ALSOsysconf(3C), pthread_attr_init(3C), attributes(5), standards(5)
Mar 23, 2005 PTHREAD_ATTR_GETGUARDSIZE(3C)
