set_sbrk_size() — sys5



SET_SBRK_SIZE(2)DOMAIN/IX Reference Manual (SYS5)SET_SBRK_SIZE(2)



NAME
     set_sbrk_size - define memory available for allocation

USAGE
     set_sbrk_size (newsize)
     int newsize;

DESCRIPTION
     The DOMAIN/IX function set_sbrk_size defines the amount of
     memory available for allocation by the memory allocation
     functions sbrk, brk, malloc, realloc, and calloc.

     Set_sbrk_size is necessary because of the differences
     between the memory management structure of DOMAIN/IX and
     that of other UNIX systems.  The DOMAIN memory allocation
     scheme is allowed to use the ``holes'' left in the address
     space when something is unmapped.  This results in non-
     contiguous virtual address space.  In order for it to
     guarantee a contiguous sbrk area, DOMAIN/IX must inform the
     kernel of the area's size at the time of the first call to
     brk(2), or sbrk(2).

     The default size of the sbrk area is 256 Kb.  Use this func-
     tion before the first call to any of the memory allocation
     functions to change the value of sbrk.

NOTES
     No sanity check is performed on (newsize) until the first
     call to brk or sbrk.  If (newsize) exceeds the amount of
     memory available when sbrk is called, sbrk will fail,
     regardless of the amount of memory requested.  Appropriate
     values for (newsize) are highly machine-dependant.  In no
     event can (newsize) exceed the difference between total map-
     pable address space and that portion of the space already
     mapped.

     If set_sbrk_size isn't called, DOMAIN/IX checks the environ-
     ment variable SBRKSIZE at the first call to brk(2) or
     sbrk(2).  If SBRKSIZE is set to a valid decimal integer,
     this becomes the sbrk size.

RELATED INFORMATION
     brk(2), sbrk(2), calloc(3), malloc(3), realloc(3) environ(7)












Printed 7/12/85                                   SET_SBRK_SIZE-1
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