NAME

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

SYNOPSIS

       #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

       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

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

ERRORS

       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).

VERSIONS

       These functions are provided by glibc since version 2.1.

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()  │               │         │
       └─────────────────────────────┴───────────────┴─────────┘

CONFORMING TO

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

NOTES

       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.

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.

EXAMPLES

       See pthread_getattr_np(3).

SEE ALSO

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

COLOPHON

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       information  about  reporting  bugs,  and  the  latest  version  of  this   page,   can   be   found   at
       https://www.kernel.org/doc/man-pages/.