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

       #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.

       The pthread_attr_setguardsize() function sets the guard size  attribute
       of the thread attributes object referred to by attr to the value speci-
       fied 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 attri-
       bute  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  attri-
       bute  of the thread attributes object referred to by attr in the buffer
       pointed to by guardsize.

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

       POSIX.1  documents an EINVAL error if attr or guardsize is invalid.  On
       Linux these functions always succeed (but portable and future-proof ap-
       plications should nevertheless handle a possible error return).

       These functions are provided by glibc since version 2.1.

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

       |Interface                    | Attribute     | Value   |
       |pthread_attr_setguardsize(), | Thread safety | MT-Safe |
       |pthread_attr_getguardsize()  |               |         |
       POSIX.1-2001, POSIX.1-2008.

       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_get-
       guardsize()  returns  the  guard size that was set by pthread_attr_set-

       Setting a guard size of 0 may be useful to save memory in  an  applica-
       tion  that creates many threads and knows that stack overflow can never

       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.

       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,  allocat-
       ing extra space at the end of the stack for the guard area.

       See pthread_getattr_np(3).

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

       This page is part of release 5.05 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
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Linux                             2017-09-15      PTHREAD_ATTR_SETGUARDSIZE(3)
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