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.TH erl_set_memory_block 3 "erts 5.6.3" "Ericsson AB" "C LIBRARY FUNCTIONS"
.SH NAME
erl_set_memory_block \- Custom memory allocation for Erlang on VxWorks(R)
.SH DESCRIPTION
.LP
This documentation is specific to VxWorks\&.
.LP
The \fIerl_set_memory_block\fR 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\&.
.LP
The memory within the block can be utilized by other tasks than Erlang\&. This is accomplished by calling the functions \fIsys_alloc\fR, \fIsys_realloc\fR and \fIsys_free\fR instead of \fImalloc\fR, \fIrealloc\fR and \fIfree\fR respectively\&.
.LP
The purpose of this is to avoid problems inherent in the VxWorks systems \fImalloc\fR 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\&.
.LP
The \fIerl_set_memory_block\fR function is callable from any C program as an ordinary 10 argument function as well as from the commandline\&.
.SH EXPORTS
.LP
.B
int erl_set_memory_block(size_t size, void *ptr, int warn_mixed_malloc, int realloc_always_moves, int use_reclaim, \&.\&.\&.)
.br
.RS
.LP
The function is called before Erlang is started to specify a large memory block where Erlang can maintain memory internally\&.
.LP
Parameters:
.RS 2
.TP 4
.B
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\&.
.TP 4
.B
void *ptr:
A pointer to the actual memory block of size \fIsize\fR\&. 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\&.
.RS 4
.LP
.LP
If a memory block is allocated and provided here, the \fIsys_alloc\fR 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 \fIuse_reclaim\fR flag\&.
.LP
.LP
If 0 is specified here, the Erlang system should not be stopped while some other task uses the memory block (has called \fIsys_alloc\fR)\&.
.RE
.TP 4
.B
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 \fImalloc\fR with \fIsys_realloc\fR or \fIsys_free\fR\&.
.TP 4
.B
int realloc_always_moves:
If this flag is set to true (anything else than 0), all calls to \fIsys_realloc\fR result in a moved memory block\&. This can in certain conditions give less fragmentation\&. This flag may be removed in future releases\&.
.TP 4
.B
int use_reclaim:
If this flag is set to true (anything else than 0), all memory allocated with \fIsys_alloc\fR 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 \fIsave_open\fR etc\&. specified in the reclaim\&.h file delivered in the Erlang distribution\&.
.RE
.LP
Return Value:
.LP
Returns 0 (OK) on success, otherwise a value <> 0\&.
.RE
.LP
.B
int erl_memory_show(\&.\&.\&.)
.br
.RS
.LP
Return Value:
.LP
Returns 0 (OK) on success, otherwise a value <> 0\&.
.RE
.LP
.B
int erl_mem_info_get(MEM_PART_STATS *stats)
.br
.RS
.LP
Parameter:
.RS 2
.TP 4
.B
MEM_PART_STATS *stats:
A pointer to a MEM_PART_STATS structure as defined in \fI<memLib\&.h>\fR\&. A successful call will fill in all fields of the structure, on error all fields are left untouched\&.
.RE
.LP
Return Value:
.LP
Returns 0 (OK) on success, otherwise a value <> 0
.RE
.SH NOTES
.LP
The memory block used by Erlang actually does not need to be inside the area known to ordinary \fImalloc\fR\&. It is possible to set the \fIUSER_RESERVED_MEM\fR 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\&.
.LP
Example:
.LP
In config\&.h for the wind kernel:
.nf
#undef LOCAL_MEM_AUTOSIZE
#undef LOCAL_MEM_SIZE
#undef USER_RESERVED_MEM
#define LOCAL_MEM_SIZE 0x05000000
#define USER_RESERVED_MEM 0x03000000
.fi
.LP
In the start-up script/code for the VxWorks node:
.nf
erl_set_memory_block(sysPhysMemTop()-sysMemTop(),sysMemTop(),0,0,1);
.fi
.LP
Setting the \fIuse_reclaim\fR 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 \fIsave_malloc\fR, \fIsave_realloc\fR and \fIsave_free\fR provide the same facilities by using VxWorks own \fImalloc\fR\&. Similar routines exist for files, see the file \fIreclaim\&.h\fR in the distribution\&.
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