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<?xml version="1.0" encoding="latin1" ?>
<!DOCTYPE cref SYSTEM "cref.dtd">
<cref>
<header>
<copyright>
<year>1998</year><year>2009</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
The contents of this file are subject to the Erlang Public License,
Version 1.1, (the "License"); you may not use this file except in
compliance with the License. You should have received a copy of the
Erlang Public License along with this software. If not, it can be
retrieved online at http://www.erlang.org/.
Software distributed under the License is distributed on an "AS IS"
basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
the License for the specific language governing rights and limitations
under the License.
</legalnotice>
<title>erl_set_memory_block</title>
<prepared>Patrik Nyblom</prepared>
<responsible></responsible>
<docno></docno>
<approved></approved>
<checked></checked>
<date>98-08-05</date>
<rev>A</rev>
<file>erl_set_memory_block.xml</file>
</header>
<lib>erl_set_memory_block</lib>
<libsummary>Custom memory allocation for Erlang on VxWorks®</libsummary>
<description>
<p>This documentation is specific to VxWorks.</p>
<p>The <c><![CDATA[erl_set_memory_block]]></c> 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.</p>
<p>The memory within the block can be utilized by other tasks than
Erlang. This is accomplished by calling the functions
<c><![CDATA[sys_alloc]]></c>, <c><![CDATA[sys_realloc]]></c> and <c><![CDATA[sys_free]]></c> instead
of <c><![CDATA[malloc]]></c>, <c><![CDATA[realloc]]></c> and <c><![CDATA[free]]></c> respectively.</p>
<p>The purpose of this is to avoid problems inherent in the
VxWorks systems <c><![CDATA[malloc]]></c> 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.</p>
<p>The <c><![CDATA[erl_set_memory_block]]></c> function is callable from any C
program as an ordinary 10 argument function as well as
from the commandline.</p>
</description>
<funcs>
<func>
<name><ret>int</ret><nametext>erl_set_memory_block(size_t size, void *ptr, int warn_mixed_malloc, int realloc_always_moves, int use_reclaim, ...)</nametext></name>
<fsummary>Specify parameters for Erlang internal memory allocation.</fsummary>
<desc>
<p>The function is called before Erlang is
started to specify a large memory block where Erlang can
maintain memory internally.</p>
<p>Parameters:</p>
<taglist>
<tag>size_t size</tag>
<item>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.</item>
<tag>void *ptr</tag>
<item>
<p>A pointer to the actual memory block of size
<c><![CDATA[size]]></c>. If this is specified as 0 (NULL), Erlang will
allocate the memory when starting and will reclaim the
memory block (as a whole) when stopped.</p>
<p>If a memory block is allocated and provided here, the
<c><![CDATA[sys_alloc]]></c> 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
<c><![CDATA[use_reclaim]]></c> flag.</p>
<p>If 0 is specified here, the Erlang system should not
be stopped while some other task uses the memory block
(has called <c><![CDATA[sys_alloc]]></c>).</p>
</item>
<tag>int warn_mixed_malloc</tag>
<item>
<p>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 <c><![CDATA[malloc]]></c> with
<c><![CDATA[sys_realloc]]></c> or <c><![CDATA[sys_free]]></c>.</p>
</item>
<tag>int realloc_always_moves</tag>
<item>
<p>If this flag is set to true (anything else than 0), all
calls to <c><![CDATA[sys_realloc]]></c> result in a moved memory
block. This can in certain conditions give less
fragmentation. This flag may be removed in future releases.</p>
</item>
<tag>int use_reclaim</tag>
<item>
<p>If this flag is set to true (anything else than 0), all
memory allocated with <c><![CDATA[sys_alloc]]></c> is automatically
reclaimed as soon as a task exits. This is very useful
to make writing port programs (and other programs as
well) easier. Combine this with using the routines
<c><![CDATA[save_open]]></c> etc. specified in the reclaim.h
file delivered in the Erlang distribution.</p>
</item>
</taglist>
<p>Return Value:</p>
<p>Returns 0 (OK) on success, otherwise a value <> 0.</p>
</desc>
</func>
<func>
<name><ret>int</ret><nametext>erl_memory_show(...)</nametext></name>
<fsummary>A utility similar to VxWorks <c><![CDATA[memShow]]></c>, but for the Erlang memory area.</fsummary>
<desc>
<p>Return Value:</p>
<p>Returns 0 (OK) on success, otherwise a value <> 0.</p>
</desc>
</func>
<func>
<name><ret>int</ret><nametext>erl_mem_info_get(MEM_PART_STATS *stats)</nametext></name>
<fsummary>A utility similar to VxWorks <c><![CDATA[memPartInfoGet]]></c>, but for the Erlang memory area.</fsummary>
<desc>
<p>Parameter:</p>
<taglist>
<tag>MEM_PART_STATS *stats</tag>
<item>A pointer to a MEM_PART_STATS structure as defined in
<c><![CDATA[<memLib.h>]]></c>. A successful call will fill in all
fields of the structure, on error all fields are left untouched. </item>
</taglist>
<p>Return Value:</p>
<p>Returns 0 (OK) on success, otherwise a value <> 0</p>
</desc>
</func>
</funcs>
<section>
<title>NOTES</title>
<p>The memory block used by Erlang actually does not need to be
inside the area known to ordinary <c><![CDATA[malloc]]></c>. It is possible
to set the <c><![CDATA[USER_RESERVED_MEM]]></c> preprocessor symbol when compiling
the wind kernel and then use user reserved memory for
Erlang. Erlang can therefor utilize memory above the 32 Mb limit
of VxWorks on the PowerPC architecture.</p>
<p>Example:</p>
<p>In config.h for the wind kernel:</p>
<code type="none"><![CDATA[
#undef LOCAL_MEM_AUTOSIZE
#undef LOCAL_MEM_SIZE
#undef USER_RESERVED_MEM
#define LOCAL_MEM_SIZE 0x05000000
#define USER_RESERVED_MEM 0x03000000
]]></code>
<p>In the start-up script/code for the VxWorks node:</p>
<code type="none"><![CDATA[
erl_set_memory_block(sysPhysMemTop()-sysMemTop(),sysMemTop(),0,0,1);
]]></code>
<p>Setting the <c><![CDATA[use_reclaim]]></c> 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 <c><![CDATA[save_malloc]]></c>,
<c><![CDATA[save_realloc]]></c> and <c><![CDATA[save_free]]></c> provide the same
facilities by using VxWorks own <c><![CDATA[malloc]]></c>. Similar routines
exist for files, see the file <c><![CDATA[reclaim.h]]></c> in the distribution.</p>
</section>
</cref>
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