pthread_attr_setguardsize(3THR) sets the guardsize of the attr object.
The guardsize argument provides protection against overflow of the stack pointer. If a thread's stack is created with guard protection, the implementation allocates extra memory at the overflow end of the stack as a buffer against stack overflow of the stack pointer. If an application overflows into this buffer an error results (possibly in a SIGSEGV signal being delivered to the thread).
The guardsize attribute is provided to the application for two reasons:
Overflow protection can potentially result in wasted system resources. An application that creates a large number of threads, and knows its threads will never overflow their stack, can save system resources by turning off guard areas.
When threads allocate large data structures on stack, a large guard area may be needed to detect stack overflow.
If guardsize is zero, a guard area will not be provided for threads created with attr. If guardsize is greater than zero, a guard area of at least size guardsize bytes is provided for each thread created with attr. By default, a thread has an implementation-defined, non-zero guard area.
A conforming implementation is permitted to round up the value contained in guardsize to a multiple of the configurable system variable PAGESIZE (see PAGESIZE in sys/mman.h). If an implementation rounds up the value of guardsize to a multiple of PAGESIZE, a call to pthread_attr_getguardsize() specifying attr will store, in guardsize, the guard size specified in the previous call to pthread_attr_setguardsize().
#include <pthread.h> int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);
pthread_attr_setguardsize() fails if:
The argument attr is invalid, the argument guardsize is invalid, or the argument guardsize contains an invalid value.