PTHREAD_ATTR_GETGUARD... BSD Library Functions Manual PTHREAD_ATTR_GETGUARD...NAME
pthread_attr_getguardsize — get and set thread guard size
LIBRARY
POSIX Threads Library (libpthread, -lpthread)
SYNOPSIS
#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 pthread_attr_getguardsize() and pthread_attr_setguardsize() functions
get and set guardsize in the attr object. If guardsize is larger than 0,
the system reserves an additional region of guarded memory of at least
guardsize bytes at the end of the thread's stack for each new thread cre‐
ated by using attr.
The guarded area is understood to be pages of memory that are protected
from read and write access. While the guarded area should be rounded by
the system page size, the actual default size is implementation-defined.
In NetBSD the default guardsize is _SC_PAGESIZE, the system page size.
The rationale behind guardsize is two-fold:
1. On the one hand, it provides protection against overflow of the
stack pointer. If there is a guard area and a thread overflows
its stack pointer into this extra memory area, it should receive a
SIGSEGV signal or experience other comparable fatal error condi‐
tion. Note that if a thread allocates large data structures on
stack, it may be necessary to raise the default guardsize in order
to detect stack overflows.
2. On the other hand, the overflow protection may waste system
resources if an application that creates a large number of threads
knows that it will never overflow the stack. In this case it is
possible to set guardsize to 0.
If pthread_attr_setstack(3) or pthread_attr_setstackaddr(3) is used to
set the stack address attribute in attr, the guard size attribute is
ignored and no guard area will be allocated; it is the responsibility of
the application to handle the overflow conditions.
RETURN VALUES
If successful, both functions return 0. Otherwise, an error number is
returned to indicate the error.
ERRORS
No errors are defined for pthread_attr_getguardsize().
The pthread_attr_setguardsize() may fail if:
[ENOMEM] There was insufficient memory.
SEE ALSOpthread_attr(3), pthread_attr_setstack(3), sysconf(3)STANDARDS
Both functions conform to IEEE Std 1003.1-2008 (“POSIX.1”).
BSD July 7, 2010 BSD
