You can use mrbconfs with following ways:

• Write them in mrbconf.h.
  • Using compiler flags is prefered when building a cross binaries or multiple mruby binaries since it's easier to use different mrbconf per each MRuby::Build.
  • Most flags can be enabled by just commenting in.
• Pass them as compiler flags.
  • Make sure you pass the same flags to all compilers since some mrbconf(e.g., MRB_GC_FIXED_ARENA) changesstruct layout and cause memory access error when C and other language(e.g., C++) is mixed.

  • stdio setting.

    ENABLE_STDIO

    • Will be defined automatically if DISABLE_STDIO isn't defined.
    • Uses <stdio.h> functions.

    DISABLE_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 file.
      • Printing features in src/print.c.

    Debug macros.

    ENABLE_DEBUG

    • 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.

    DISABLE_DEBUG

    • Will be define automatically if ENABLE_DEBUG isn't defined.

    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.
    • Else 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_FLOAT

    • When defined single precision floating point type(C type float) is used as mrb_float.
    • Else double precision floating point type(C type double) is used as mrb_float.

    MRB_INT16

    • When defined int16_t will be defined as mrb_int.
    • Conflicts with MRB_INT64.

    MRB_INT64

    • When defined int64_t will be defined as mrb_int.
    • Conflicts with MRB_INT16.
    • When MRB_INT16 or MRB_INT64 isn't defined int(most of the times 32-bit integer) will be defined as mrb_int.

    Garbage collector configuration.

    MRB_GC_STRESS

    • When defined full GC is emitted per each RBasic allocation.
    • Mainly used in memory manager debugging.

    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.

    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 exceedsMRB_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_FLOAT.

    MRB_WORD_BOXING

    • If defined represent mrb_value as a word.
    • If defined Float will be a mruby object with RBasic.

    Instance variable configuration.

    MRB_USE_IV_SEGLIST

    • If defined enable segmented list in instance variable table instead of khash.
    • Segmented list is a linked list of key and value segments.
    • It will linear search instead of hash search.

    MRB_SEGMENT_SIZE

    • Default value is 4.
    • Specifies size of each segment in segment list.
    • Ignored when MRB_USE_IV_SEGLIST isn't defined.

    MRB_IVHASH_INIT_SIZE

    • Default value is 8.
    • Specifies initial size for instance variable table.
    • Ignored when MRB_USE_IV_SEGLIST is defined.

    Other configuration.

    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_STR_BUF_MIN_SIZE

    • Default value is 128.
    • Specifies initial capacity of RString created by mrb_str_buf_new function..