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   pthread_attr_getguardsize    ( 3 )

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)