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NetBSD 6.1.5 - man page for pthread_attr_setguardsize (netbsd section 3)

PTHREAD_ATTR_GETGUARDSIZE(3)	   BSD Library Functions Manual      PTHREAD_ATTR_GETGUARDSIZE(3)

NAME
     pthread_attr_getguardsize -- get and set thread guard size

LIBRARY
     POSIX Threads Library (libpthread, -lpthread)

SYNOPSIS
     #include <pthread.h>

     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 addi-
     tional 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 applica-
	    tion 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'').

BSD					   July 7, 2010 				      BSD


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