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


     , size_t int pthread_attr_setguardsize(pthread_attr_t
*attr , size_t *int pthread_attr_getguardsize(const
pthread_attr_t *attr

     Compile and link with −pthread.

The function sets the guard size attribute of the thread
attributes object referred to by attr to the value specified

     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

     If the stack address attribute has been set in attr
(using or 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 to manually define a guard area at the end
of the stack that it has allocated).

     The function returns the guard size attribute of the
thread attributes object referred to by attr in the buffer
pointed to by

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   │
│                             │ Thread safety MT‐Safe │

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, returns
the guard size that was set by

     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.

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 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.


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