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)