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erl_set_memory_block(3erl)	       C Library Functions	       erl_set_memory_block(3erl)

       erl_set_memory_block - Custom memory allocation for Erlang on VxWorks(R)

       This documentation is specific to VxWorks.

       The  erl_set_memory_block  function/command  initiates  custom  memory  allocation for the
       Erlang emulator. It has to be called before the	Erlang	emulator  is  started  and  makes
       Erlang use one single large memory block for all memory allocation.

       The  memory  within  the  block can be utilized by other tasks than Erlang. This is accom-
       plished by calling the functions sys_alloc , sys_realloc and sys_free instead of malloc	,
       realloc and free respectively.

       The  purpose  of this is to avoid problems inherent in the VxWorks systems malloc library.
       The memory allocation within the large memory  block  avoids  fragmentation  by	using  an
       "address order first fit" algorithm. Another advantage of using a separate memory block is
       that resource reclamation can be made more easily when Erlang is stopped.

       The erl_set_memory_block function is callable from any C program as an ordinary	10  argu-
       ment function as well as from the commandline.

       int   erl_set_memory_block(size_t  size,  void  *ptr,  int  warn_mixed_malloc,  int  real-
       loc_always_moves, int use_reclaim, ...)

	      The function is called before Erlang is started to specify  a  large  memory  block
	      where Erlang can maintain memory internally.


		size_t size :
		  The  size in bytes of Erlang's internal memory block. Has to be specified. Note
		  that the VxWorks system uses dynamic memory allocation heavily, so  leave  some
		  memory to the system.

		void *ptr :
		  A  pointer  to the actual memory block of size size . If this is specified as 0
		  (NULL), Erlang will allocate the memory when starting and will reclaim the mem-
		  ory block (as a whole) when stopped.

		  If  a  memory  block is allocated and provided here, the sys_alloc etc routines
		  can still be used after the Erlang emulator is stopped. The Erlang emulator can
		  also	be restarted while other tasks using the memory block are running without
		  destroying the memory. If Erlang is to be restarted, also set  the  use_reclaim

		  If  0  is  specified	here,  the Erlang system should not be stopped while some
		  other task uses the memory block (has called sys_alloc ).

		int warn_mixed_malloc :
		  If this flag is set to true (anything else than 0), the  system  will  write	a
		  warning  message  on	the  console  if  a  program is mixing normal malloc with
		  sys_realloc or sys_free .

		int realloc_always_moves :
		  If this flag is set to true (anything else than 0), all  calls  to  sys_realloc
		  result  in a moved memory block. This can in certain conditions give less frag-
		  mentation. This flag may be removed in future releases.

		int use_reclaim :
		  If this flag is set to true (anything else than 0), all memory  allocated  with
		  sys_alloc is automatically reclaimed as soon as a task exits. This is very use-
		  ful to make writing port programs (and other programs as well) easier.  Combine
		  this	with  using  the  routines save_open etc. specified in the reclaim.h file
		  delivered in the Erlang distribution.

	      Return Value:

	      Returns 0 (OK) on success, otherwise a value <> 0.

       int erl_memory_show(...)

	      Return Value:

	      Returns 0 (OK) on success, otherwise a value <> 0.

       int erl_mem_info_get(MEM_PART_STATS *stats)


		MEM_PART_STATS *stats :
		  A pointer to a MEM_PART_STATS structure as defined in <memLib.h> . A successful
		  call	will  fill  in	all fields of the structure, on error all fields are left

	      Return Value:

	      Returns 0 (OK) on success, otherwise a value <> 0

       The memory block used by Erlang actually does not need to be  inside  the  area	known  to
       ordinary  malloc  .  It	is possible to set the USER_RESERVED_MEM preprocessor symbol when
       compiling the wind kernel and then use user reserved memory for Erlang. Erlang can  there-
       for utilize memory above the 32 Mb limit of VxWorks on the PowerPC architecture.


       In config.h for the wind kernel:

	     #undef LOCAL_MEM_SIZE
	     #undef USER_RESERVED_MEM

	     #define LOCAL_MEM_SIZE	   0x05000000
	     #define USER_RESERVED_MEM	   0x03000000

       In the start-up script/code for the VxWorks node:


       Setting	the  use_reclaim  flag decreases performance of the system, but makes programming
       much easier. Other similar facilities are present in the Erlang system even without  using
       a separate memory block. The routines called save_malloc , save_realloc and save_free pro-
       vide the same facilities by using VxWorks own malloc . Similar routines exist  for  files,
       see the file reclaim.h in the distribution.

Ericsson AB				    erts 5.8.3		       erl_set_memory_block(3erl)
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