получить и установить атрибут threadguardsize (get and set the thread guardsize attribute)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
pthread_attr_getguardsize, pthread_attr_setguardsize — get and
set the thread guardsize attribute
Синопсис (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);
Описание (Description)
The pthread_attr_getguardsize() function shall get the guardsize
attribute in the attr object. This attribute shall be returned in
the guardsize parameter.
The pthread_attr_setguardsize() function shall set the guardsize
attribute in the attr object. The new value of this attribute
shall be obtained from the guardsize parameter. If guardsize is
zero, a guard area shall not be provided for threads created with
attr. If guardsize is greater than zero, a guard area of at
least size guardsize bytes shall be provided for each thread
created with attr.
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 shall result
(possibly in a SIGSEGV signal being delivered to the thread).
A conforming implementation may round up the value contained in
guardsize to a multiple of the configurable system variable
{PAGESIZE} (see <sys/mman.h>). If an implementation rounds up
the value of guardsize to a multiple of {PAGESIZE}, a call to
pthread_attr_getguardsize() specifying attr shall 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 implementation-
defined.
If the stackaddr attribute has been set (that is, the caller is
allocating and managing its own thread stacks), the guardsize
attribute shall be ignored and no protection shall 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.
The behavior is undefined if the value specified by the attr
argument to pthread_attr_getguardsize() or
pthread_attr_setguardsize() does not refer to an initialized
thread attributes object.
Возвращаемое значение (Return value)
If successful, the pthread_attr_getguardsize() and
pthread_attr_setguardsize() functions shall return zero;
otherwise, an error number shall be returned to indicate the
error.
Ошибки (Error)
These functions shall fail if:
EINVAL The parameter guardsize is invalid.
These functions shall not return an error code of [EINTR].
The following sections are informative.
Примеры (Examples)
Retrieving the guardsize Attribute
This example shows how to obtain the guardsize attribute of a
thread attribute object.
#include <pthread.h>
pthread_attr_t thread_attr;
size_t guardsize;
int rc;
/* code initializing thread_attr */
...
rc = pthread_attr_getguardsize (&thread_attr, &guardsize);
if (rc != 0) {
/* handle error */
...
}
else {
if (guardsize > 0) {
/* a guard area of at least guardsize bytes is provided */
...
}
else {
/* no guard area provided */
...
}
}
Использование в приложениях (Application usage)
None.
Обоснование (Rationale)
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 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 default size of the guard area is left implementation-defined
since on systems supporting very large page sizes, the overhead
might be substantial if at least one guard page is required by
default.
If an implementation detects that the value specified by the attr
argument to pthread_attr_getguardsize() or
pthread_attr_setguardsize() does not refer to an initialized
thread attributes object, it is recommended that the function
should fail and report an [EINVAL] error.
Будущие направления (Future directions)
None.
Смотри также (See also)
The Base Definitions volume of POSIX.1‐2017, pthread.h(0p),
sys_mman.h(0p)
