Updated: 2021/Apr/14

PTHREAD_ATTR_GETGUARDSIZE(3)                          Library Functions Manual

     pthread_attr_getguardsize, pthread_attr_setguardsize - get and set thread
     guard size

     POSIX Threads Library (libpthread, -lpthread)

     #include <pthread.h>

     pthread_attr_getguardsize(const pthread_attr_t * restrict attr,
         size_t * restrict guardsize);

     pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);

     The pthread_attr_getguardsize() and pthread_attr_setguardsize() functions
     get and set guardsize in the attr object.  If guardsize is larger than 0,
     the system reserves an additional region of guarded memory of at least
     guardsize bytes at the end of the thread's stack for each new thread
     created by using attr.

     The guarded area is understood to be pages of memory that are protected
     from read and write access.  While the guarded area should be rounded by
     the system page size, the actual default size is implementation-defined.
     In NetBSD the default guardsize is given by the vm.thread_guard_size

     The rationale behind guardsize is two-fold:

       1.   On the one hand, it provides protection against overflow of the
            stack pointer.  If there is a guard area and a thread overflows
            its stack pointer into this extra memory area, it should receive a
            SIGSEGV signal or experience other comparable fatal error
            condition.  Note that if a thread allocates large data structures
            on stack, it may be necessary to raise the default guardsize in
            order to detect stack overflows.

       2.   On the other hand, the overflow protection may waste system
            resources if an application that creates a large number of threads
            knows that it will never overflow the stack.  In this case it is
            possible to set guardsize to 0.

     If pthread_attr_setstack(3) or pthread_attr_setstackaddr(3) is used to
     set the stack address attribute in attr, the guard size attribute is
     ignored and no guard area will be allocated; it is the responsibility of
     the application to handle the overflow conditions.

     If successful, both functions return 0.  Otherwise, an error number is
     returned to indicate the error.

     No errors are defined for pthread_attr_getguardsize().

     The pthread_attr_setguardsize() may fail if:

     [ENOMEM]           There was insufficient memory.

     pthread_attr(3), pthread_attr_setstack(3), sysconf(3)

     Both functions conform to IEEE Std 1003.1-2008 ("POSIX.1").

NetBSD 9.99                      July 2, 2017                      NetBSD 9.99