pthread_attr_setguardsize(3) - Linux manual page (original) (raw)
pthread...guardsize(3) Library Functions Manual pthread...guardsize(3)
NAME top
pthread_attr_setguardsize, pthread_attr_getguardsize - set/get
guard size attribute in thread attributes objectLIBRARY top
POSIX threads library (_libpthread_, _-lpthread_)SYNOPSIS top
**#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_**);**DESCRIPTION top
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)](../man3/pthread%5Fattr%5Fsetstack.3.html) or [pthread_attr_setstackaddr(3)](../man3/pthread%5Fattr%5Fsetstackaddr.3.html)), 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)](../man2/mprotect.2.html) 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_.RETURN VALUE top
On success, these functions return 0; on error, they return a
nonzero error number.ERRORS top
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).ATTRIBUTES top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ **Interface** │ **Attribute** │ **Value** │
├──────────────────────────────────────┼───────────────┼─────────┤
│ **pthread_attr_setguardsize**(), │ Thread safety │ MT-Safe │
│ **pthread_attr_getguardsize**() │ │ │
└──────────────────────────────────────┴───────────────┴─────────┘STANDARDS top
POSIX.1-2008.HISTORY top
glibc 2.1. POSIX.1-2001.NOTES top
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_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 stack.BUGS top
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)](../man3/pthread%5Fcreate.3.html) 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 top
See [pthread_getattr_np(3)](../man3/pthread%5Fgetattr%5Fnp.3.html).SEE ALSO top
[mmap(2)](../man2/mmap.2.html), [mprotect(2)](../man2/mprotect.2.html), [pthread_attr_init(3)](../man3/pthread%5Fattr%5Finit.3.html),
[pthread_attr_setstack(3)](../man3/pthread%5Fattr%5Fsetstack.3.html), [pthread_attr_setstacksize(3)](../man3/pthread%5Fattr%5Fsetstacksize.3.html),
[pthread_create(3)](../man3/pthread%5Fcreate.3.html), [pthreads(7)](../man7/pthreads.7.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 pthread...guardsize(3)
Pages that refer to this page:pthread_attr_init(3), pthread_attr_setstack(3), pthread_attr_setstacksize(3), pthread_getattr_default_np(3), pthread_getattr_np(3)