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PTHREAD_ATTR_GETGUARDSIZE(3)                          Library Functions Manual

NAME
     pthread_attr_getguardsize -- get and set thread guard size

LIBRARY
     POSIX Threads Library (libpthread, -lpthread)

SYNOPSIS
     #include <&lt;pthread.h>&gt;

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

     int
     pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);

DESCRIPTION
     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 _SC_PAGESIZE, the system page 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.

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

ERRORS
     No errors are defined for pthread_attr_getguardsize().

     The pthread_attr_setguardsize() may fail if:

     [ENOMEM]           There was insufficient memory.

SEE ALSO
     pthread_attr(3), pthread_attr_setstack(3), sysconf(3)

STANDARDS
     Both functions conform to IEEE Std 1003.1-2008 (``POSIX.1'').

NetBSD 6.1.5                     July 7, 2010                     NetBSD 6.1.5