pthread_attr_setguardsize, pthread_attr_getguardsize - set/get guard size
attribute in thread attributes object
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.
() function sets the guard size attribute of
the thread attributes object referred to by attr
to the value specified
is greater than 0, then for each new thread created using
the system allocates an additional region of at least
bytes at the end of the thread's stack to act as the guard
area for the stack (but see BUGS).
is 0, then new threads created with attr
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
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).
() 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
POSIX.1-2001 documents an EINVAL
error if attr
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.
Multithreading (see pthreads(7))¶
() and pthread_attr_getguardsize
functions are thread-safe.
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
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_setguardsize
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
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.
This page is part of release 3.74 of the Linux man-pages
description of the project, information about reporting bugs, and the latest
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