pthread_attr_setguardsize, pthread_attr_getguardsize — set/get guard size attribute in thread attributes object
||const pthread_attr_t *attr,|
Compile and link with
pthread_attr_setguardsize() function sets
the guard size attribute of the thread attributes object
referred to by
to the value specified in
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).
guardsize is 0,
then new threads created with
attr will not have a guard
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
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
returns the guard size attribute of the thread attributes
object referred to by
attr in the buffer pointed to
POSIX.1 documents an EINVAL
guardsize is invalid.
On Linux these functions always succeed (but portable and
future-proof applications should nevertheless handle a
possible error return).
For an explanation of the terms used in this section, see attributes(7).
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
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 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.
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Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
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