1PTHREAD_ATTR_SETGUARDSIZE(3)Linux Programmer's ManuaPlTHREAD_ATTR_SETGUARDSIZE(3)
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NAME

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

10       #include <pthread.h>
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12       int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);
13       int pthread_attr_getguardsize(const pthread_attr_t *attr,
14                                     size_t *guardsize);
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16       Compile and link with -pthread.
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DESCRIPTION

19       The pthread_attr_setguardsize() function sets the guard size  attribute
20       of the thread attributes object referred to by attr to the value speci‐
21       fied in guardsize.
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23       If guardsize is greater than 0, then for each new thread created  using
24       attr  the  system  allocates an additional region of at least guardsize
25       bytes at the end of the thread's stack to act as the guard area for the
26       stack (but see BUGS).
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28       If  guardsize  is 0, then new threads created with attr will not have a
29       guard area.
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31       The default guard size is the same as the system page size.
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33       If  the  stack  address  attribute  has  been  set   in   attr   (using
34       pthread_attr_setstack(3) or pthread_attr_setstackaddr(3)), meaning that
35       the caller is allocating the thread's stack, then the guard size attri‐
36       bute  is  ignored (i.e., no guard area is created by the system): it is
37       the application's responsibility to handle stack overflow  (perhaps  by
38       using  mprotect(2)  to  manually  define a guard area at the end of the
39       stack that it has allocated).
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41       The pthread_attr_getguardsize() function returns the guard size  attri‐
42       bute  of the thread attributes object referred to by attr in the buffer
43       pointed to by guardsize.
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RETURN VALUE

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

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

55       These functions are provided by glibc since version 2.1.
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ATTRIBUTES

58       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
59       tributes(7).
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61       ┌─────────────────────────────┬───────────────┬─────────┐
62Interface                    Attribute     Value   
63       ├─────────────────────────────┼───────────────┼─────────┤
64pthread_attr_setguardsize(), │ Thread safety │ MT-Safe │
65pthread_attr_getguardsize()  │               │         │
66       └─────────────────────────────┴───────────────┴─────────┘

CONFORMING TO

68       POSIX.1-2001, POSIX.1-2008.
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NOTES

71       A  guard  area  consists  of virtual memory pages that are protected to
72       prevent read and write access.  If a thread overflows  its  stack  into
73       the guard area, then, on most hard architectures, it receives a SIGSEGV
74       signal, thus notifying it of the overflow.  Guard areas start  on  page
75       boundaries,  and  the guard size is internally rounded up to the system
76       page size when creating  a  thread.   (Nevertheless,  pthread_attr_get‐
77       guardsize()  returns  the  guard size that was set by pthread_attr_set‐
78       guardsize().)
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80       Setting a guard size of 0 may be useful to save memory in  an  applica‐
81       tion  that creates many threads and knows that stack overflow can never
82       occur.
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84       Choosing a guard size larger than the default size may be necessary for
85       detecting  stack  overflows if a thread allocates large data structures
86       on the stack.
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BUGS

89       As at glibc 2.8, the NPTL threading implementation includes  the  guard
90       area  within  the  stack  size allocation, rather than allocating extra
91       space at the end of the stack, as POSIX.1 requires.  (This  can  result
92       in  an  EINVAL  error from pthread_create(3) if the guard size value is
93       too large, leaving no space for the actual stack.)
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95       The obsolete LinuxThreads implementation did the right thing,  allocat‐
96       ing extra space at the end of the stack for the guard area.
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EXAMPLES

99       See pthread_getattr_np(3).
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SEE ALSO

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

106       This page is part of release 5.10 of the Linux  man-pages  project.   A
107       description  of  the project, information about reporting bugs, and the
108       latest    version    of    this    page,    can     be     found     at
109       https://www.kernel.org/doc/man-pages/.
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113Linux                             2020-06-09      PTHREAD_ATTR_SETGUARDSIZE(3)
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