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 created 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
given by the
vm.thread_guard_size
sysctl(7).
The rationale behind
guardsize is two-fold:
- 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 condition. 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.
- 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 ALSO
pthread_attr(3),
pthread_attr_setstack(3),
sysconf(3)
STANDARDS
Both functions conform to
IEEE Std 1003.1-2008
(“POSIX.1”).