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mruby-mruby/doc/guides/mrbconf.md
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dearblue f6c9191cd0 Replace MRB_NO_DIRECT_THREADING with MRB_USE_VM_SWITCH_DISPATCH 
The correct technique now is "Token Threading".
However, the new name was chosen because it was felt that if a different technique was added in the future, there would be no need to replace it.
2023-03-18 17:39:41 +09:00

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# mruby configuration macros
## The configuration file
You can do the build configuration in the build configuration file. The default
configuration file is `build_config/default.rb`.
You can specify your own configuration file by the `MRUBY_CONFIG` environment
variable (you can use `CONFIG` for shorthand for `MRUBY_CONFIG`). If the path
doesn't exist, `build_config/${MRUBY_CONFIG}.rb` is used.
## How to use these macros
Just add the configuration value to the `MRuby::Build#defines` attribute.
This is the same for `MRuby::CrossBuild`.
```ruby
# build_config.rb
MRuby::Build.new do |conf|
.....
conf.defines << 'MRB_GC_FIXED_ARENA'
conf.defines << 'MRB_NO_METHOD_CACHE'
.....
end
```
***NOTE***
- Use common definitions (`conf.defines`) instead of per-compiler definitions (e.g., `conf.cc.defines`) unless there is a special reason not to.
- It is now deprecated to edit the `include/mruby/mrbconf.h` file or give it directly as a compiler flag, as was the case before.
## stdio setting
`MRB_NO_STDIO`
- When defined `<stdio.h>` functions won't be used.
- Some features will be disabled when this is enabled:
- `mrb_irep` load/dump from/to file.
- Compiling mruby script from a file.
- Printing features in **src/print.c**.
## Debug macros
`MRB_USE_DEBUG_HOOK`
- When defined code fetch hook and debug OP hook will be enabled.
- When using any of the hook set function pointer `code_fetch_hook` and/or `debug_op_hook` of `mrb_state`.
- Fetch hook will be called before any OP.
- Debug OP hook will be called when dispatching `OP_DEBUG`.
`MRB_DEBUG`
- When defined `mrb_assert*` macro will be defined with macros from `<assert.h>`.
- Could be enabled via `enable_debug` method of `MRuby::Build`.
## Stack configuration
`MRB_STACK_EXTEND_DOUBLING`
- If defined doubles the stack size when extending it.
- Otherwise extends stack with `MRB_STACK_GROWTH`.
`MRB_STACK_GROWTH`
- Default value is `128`.
- Used in stack extending.
- Ignored when `MRB_STACK_EXTEND_DOUBLING` is defined.
`MRB_STACK_MAX`
- Default value is `0x40000 - MRB_STACK_GROWTH`.
- Raises `RuntimeError` when stack size exceeds this value.
## Primitive type configuration
`MRB_USE_FLOAT32`
- When defined single-precision floating-point type(C type `float`) is used as `mrb_float`.
- Otherwise, double-precision floating-point type(C type `double`) is used as `mrb_float`.
`MRB_NO_FLOAT`
- When defined removes floating-point numbers from mruby.
- It makes mruby easier to handle in "Micro-controller without FPU" and "Kernel Space".
`MRB_INT32`
- When defined, or `MRB_INT64` are not defined on 32-bit CPU mode, `mrb_int` will be defined as `int32_t`.
- Conflicts with `MRB_INT64`.
`MRB_INT64`
- When defined, or `MRB_INT32` are not defined on 64-bit CPU mode, `mrb_int` will be defined as `int64_t`.
- Conflicts with `MRB_INT32`.
## Garbage collector configuration
`MRB_GC_STRESS`
- When defined full GC is emitted per each `RBasic` allocation.
- Mainly used in memory manager debugging.
- If defined at the same time as `MRB_DEBUG`, full GC is emitted also per each heap allocation (`mrb_malloc()` or etc.).
This configuration slows down mruby execution by a factor of 2 to 3 or even more.
`MRB_GC_TURN_OFF_GENERATIONAL`
- When defined turns generational GC by default.
`MRB_GC_FIXED_ARENA`
- When defined used fixed size GC arena.
- Raises `RuntimeError` when this is defined and GC arena size exceeds `MRB_GC_ARENA_SIZE`.
- Useful tracking unnecessary mruby object allocation.
`MRB_GC_ARENA_SIZE`
- Default value is `100`.
- Ignored when `MRB_GC_FIXED_ARENA` isn't defined.
- Defines fixed GC arena size.
`MRB_HEAP_PAGE_SIZE`
- Defines value is `1024`.
- Specifies number of `RBasic` per each heap page.
- To calculate the number of bytes per heap page, it is "(size of management data per heap page) + (size per object) * `MRB_HEAP_PAGE_SIZE`".
In mruby 3.1.0, the "size of management data per heap page" is 6 words, also "size per object" is 6 words.
For a 32-bit CPU, `(6 * 4) + (6 * 4) * MRB_HEAP_PAGE_SIZE` gives the bytes of size per heap page.
Conversely, for example, to keep the size per heap page to 4 Ki bytes,
calculate `(4096 - (6 * 4)) / (6 * 4)` to specify `MRB_HEAP_PAGE_SIZE=169`.
## Memory pool configuration
`POOL_ALIGNMENT`
- Default value is `4`.
- If you're allocating data types that requires alignment more than default value define the
largest value of required alignment.
`POOL_PAGE_SIZE`
- Default value is `16000`.
- Specifies page size of pool page.
- Smaller the value is increases memory overhead.
## State atexit configuration
`MRB_FIXED_STATE_ATEXIT_STACK`
- If defined enables fixed size `mrb_state` atexit stack.
- Raises `RuntimeError` when `mrb_state_atexit` call count to same `mrb_state` exceeds
`MRB_FIXED_STATE_ATEXIT_STACK_SIZE`'s value.
`MRB_FIXED_STATE_ATEXIT_STACK_SIZE`
- Default value is `5`.
- If `MRB_FIXED_STATE_ATEXIT_STACK` isn't defined this macro is ignored.
## `mrb_value` configuration
`MRB_ENDIAN_BIG`
- If defined compiles mruby for big endian machines.
- Used in `MRB_NAN_BOXING`.
- Some mrbgem use this mrbconf.
`MRB_NAN_BOXING`
- If defined represent `mrb_value` in boxed `double`.
- Conflicts with `MRB_USE_FLOAT32` and `MRB_NO_FLOAT`.
`MRB_WORD_BOXING`
- If defined represent `mrb_value` as a word.
- If defined `Float` will be a mruby object with `RBasic`.
## Reduce heap memory configuration
`MRB_USE_ETEXT_RO_DATA_P`
- Use `etext` and `edata` section addresses defined by the linker to detect read-only data.
- Those addresses are widely available, but not portable, nor standardized.
- This macro is defined by default on User-mode Linux.
`MRB_NO_DEFAULT_RO_DATA_P`
- Define this macro when the default `mrb_ro_data_p()` does not work for any reason.
`MRB_USE_CUSTOM_RO_DATA_P`
- Please try if `MRB_USE_LINK_TIME_RO_DATA_P` is not available.
- The `mrb_ro_data_p()` function is implemented by the user in an arbitrary file.
- The prototype declaration is `mrb_bool mrb_ro_data_p(const char *ptr)`.
- Return `TRUE` if `ptr` is in the read-only section, otherwise return `FALSE`.
## Other configuration
`MRB_MALLOC_TRIM`
- call malloc_trim(0) for each mrb_full_gc() call
`MRB_UTF8_STRING`
- Adds UTF-8 encoding support to character-oriented String instance methods.
- If it isn't defined, they only support the US-ASCII encoding.
`MRB_STR_LENGTH_MAX`
- The maximum length of strings (default 1MB)
- set this value to zero to skip the check
`MRB_ARY_LENGTH_MAX`
- The maximum length of strings (default 1MB)
- set this value to zero to skip the check
`MRB_FUNCALL_ARGC_MAX`
- Default value is `16`.
- Specifies 4th argument(`argc`) max value of `mrb_funcall`.
- Raises `ArgumentError` when the `argc` argument is bigger then this value `mrb_funcall`.
`KHASH_DEFAULT_SIZE`
- Default value is `32`.
- Specifies default size of khash table bucket.
- Used in `kh_init_ ## name` function.
`MRB_NO_METHOD_CACHE`
- Disable method cache to save memory.
`MRB_METHOD_CACHE_SIZE`
- Default value is `256`.
- Ignored if `MRB_NO_METHOD_CACHE` is defined.
- Need to be the power of 2.
`MRB_USE_METHOD_T_STRUCT`
- Use C struct to represent `mrb_method_t`
- No `MRB_USE_METHOD_T_STRUCT` requires highest 2 bits of function pointers to be zero
- Define this macro on machines that use higher bits of pointers
`MRB_USE_ALL_SYMBOLS`
- Make it available `Symbol.all_symbols` in `mrbgems/mruby-symbol-ext`
- Increase heap memory usage.
`MRB_USE_VM_SWITCH_DISPATCH`
- Turn on switch dispatch in VM loop
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