NAME
pthreadattrsetguardsize, pthreadattrgetguardsize - set/get guard size attribute in thread attributes object SYNOPSIS
#include
int pthreadattrsetguardsize(pthreadattrt *attr, sizet guardsize); int pthreadattrgetguardsize(pthreadattrt *attr, sizet *guardsize); Compile and link with -pthread. DESCRIPTION The pthreadattrsetguardsize() function sets the guard size attribute of the thread attributes object referred to by attr to the value speci‐ fied 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 pthreadattrsetstack(3) or pthreadattrsetstackaddr(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 pthreadattrgetguardsize() function returns the guard size attribute of the thread attributes object referred to by attr in the buffer pointed to by guardsize. RETURN VALUE On success, these functions return 0; on error, they return a nonzero error number. ERRORS
POSIX.1-2001 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 │ ├─────────────────────────────┼───────────────┼─────────┤
│pthreadattrsetguardsize(), │ Thread safety │ MT-Safe │ │pthreadattrgetguardsize() │ │ │ └─────────────────────────────┴───────────────┴─────────┘ CONFORMING TO
POSIX.1-2001. 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, pthreadattrget‐ guardsize() returns the guard size that was set by pthreadattrset‐ guardsize().) Setting a guard size of 0 may be useful to save memory in an applica‐ tion 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 pthreadcreate(3) if the guard size value is too large, leaving no space for the actual stack.) The obsolete LinuxThreads implementation did the right thing, allocat‐ ing extra space at the end of the stack for the guard area. EXAMPLE See pthreadgetattrnp(3). SEE ALSO mmap(2), mprotect(2), pthreadattrinit(3), pthreadattrsetstack(3), pthreadattrsetstacksize(3), pthreadcreate(3), pthreads(7) COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2008-10-24 PTHREADATTRSETGUARDSIZE(3)