установить / получить атрибут размера защиты в объекте атрибутов потока (set/get guard size attribute in thread attributes object)
Имя (Name)
pthread_attr_setguardsize, pthread_attr_getguardsize - set/get
guard size attribute in thread attributes object
Синопсис (Synopsis)
#include <pthread.h>
int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);
int pthread_attr_getguardsize(const pthread_attr_t *restrict attr,
size_t *restrict guardsize);
Compile and link with -pthread.
Описание (Description)
The pthread_attr_setguardsize() function sets the guard size
attribute of the thread attributes object referred to by attr to
the value specified in guardsize.
If guardsize is greater than 0, then for each new thread created
using attr the system allocates an additional region of at least
guardsize bytes at the end of the thread's stack to act as the
guard area for the stack (but see BUGS).
If guardsize is 0, then new threads created with attr will not
have a guard area.
The default guard size is the same as the system page size.
If the stack address attribute has been set in attr (using
pthread_attr_setstack(3) or pthread_attr_setstackaddr(3)),
meaning that the caller is allocating the thread's stack, then
the guard size attribute is ignored (i.e., no guard area is
created by the system): it is the application's responsibility to
handle stack overflow (perhaps by using mprotect(2) to manually
define a guard area at the end of the stack that it has
allocated).
The pthread_attr_getguardsize() function returns the guard size
attribute of the thread attributes object referred to by attr in
the buffer pointed to by guardsize.
Возвращаемое значение (Return value)
On success, these functions return 0; on error, they return a
nonzero error number.
Ошибки (Error)
POSIX.1 documents an EINVAL error if attr or guardsize is
invalid. On Linux these functions always succeed (but portable
and future-proof applications should nevertheless handle a
possible error return).
Версии (Versions)
These functions are provided by glibc since version 2.1.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│pthread_attr_setguardsize(), │ Thread safety │ MT-Safe │
│pthread_attr_getguardsize() │ │ │
└──────────────────────────────────────┴───────────────┴─────────┘
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008.
Примечание (Note)
A guard area consists of virtual memory pages that are protected
to prevent read and write access. If a thread overflows its
stack into the guard area, then, on most hard architectures, it
receives a SIGSEGV signal, thus notifying it of the overflow.
Guard areas start on page boundaries, and the guard size is
internally rounded up to the system page size when creating a
thread. (Nevertheless, pthread_attr_getguardsize() returns the
guard size that was set by pthread_attr_setguardsize().)
Setting a guard size of 0 may be useful to save memory in an
application that creates many threads and knows that stack
overflow can never occur.
Choosing a guard size larger than the default size may be
necessary for detecting stack overflows if a thread allocates
large data structures on the stack.
Ошибки (баги) (Bugs)
As at glibc 2.8, the NPTL threading implementation includes the
guard area within the stack size allocation, rather than
allocating extra space at the end of the stack, as POSIX.1
requires. (This can result in an EINVAL error from
pthread_create(3) if the guard size value is too large, leaving
no space for the actual stack.)
The obsolete LinuxThreads implementation did the right thing,
allocating extra space at the end of the stack for the guard
area.
Примеры (Examples)
See pthread_getattr_np(3).
Смотри также (See also)
mmap(2), mprotect(2), pthread_attr_init(3),
pthread_attr_setstack(3), pthread_attr_setstacksize(3),
pthread_create(3), pthreads(7)
