NAME         top

       pthread_attr_setguardsize,  pthread_attr_getguardsize - set/get guard
       size attribute in thread attributes object

SYNOPSIS         top

       #include <pthread.h>

       int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);
       int pthread_attr_getguardsize(const pthread_attr_t *attr, size_t *guardsize);

       Compile and link with -pthread.

DESCRIPTION         top

       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.

RETURN VALUE         top

       On success, these functions return 0; on error, they return a nonzero
       error number.

ERRORS         top

       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

VERSIONS         top

       These functions are provided by glibc since version 2.1.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface                    Attribute     Value   │
       │pthread_attr_setguardsize(), │ Thread safety │ MT-Safe │
       │pthread_attr_getguardsize()  │               │         │

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008.

NOTES         top

       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

       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.

BUGS         top

       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.

EXAMPLE         top

       See pthread_getattr_np(3).

SEE ALSO         top

       mmap(2), mprotect(2), pthread_attr_init(3), pthread_attr_setstack(3),
       pthread_attr_setstacksize(3), pthread_create(3), pthreads(7)

COLOPHON         top

       This page is part of release 4.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                            2015-08-08     PTHREAD_ATTR_SETGUARDSIZE(3)