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PTHREAD_ATTR_SETGUARDSIZE(3)                                            Linux Programmer's Manual                                           PTHREAD_ATTR_SETGUARDSIZE(3)

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 *restrict attr,
                                     size_t *restrict 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  guard‐
       size.

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(), pthread_attr_getguardsize()                                                                              │ Thread safety │ MT-Safe │
       └──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

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_set‐
       guardsize().)

       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)

Linux                                                                          2021-03-22                                                   PTHREAD_ATTR_SETGUARDSIZE(3)

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