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     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
     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.


     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
     applications 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
     |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 4.16 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


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